Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: wsscott on March 28, 2020, 09:41:48 am
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I'm a hobbyist level builder, but I built a Weber 5F1 kit that worked first time with no issues, and I built an Echo-Matic delay unit, and also a Maestro Fuzztone. I had issues with the last 2 builds, but finally found my wiring misses and got them fixed, and they sound great. So I have confidence in my assembling ability. My question is related to your thoughts on what I'd like to do now.
I want to have a separate vibrato/reverb to go with my 5F1 Champ, and I really love the Magnatone Pitch-Shifting Vibrato. I've looked at the Weber ReVibe kit, and its pretty much what I'm looking for except for the Vibrato. So I wanted to get ideas on how to take a Magnatone Vibrato circuit and plug it into a Reverb circuit--whether the reverb circuit is the ReVibe's or something else doesn't matter. Your thoughts on this project and issues would be appreciated. Thanks.
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Welcome.
Folks here are forgetful and lazy. Do I have all Maggies and Champs memorized? Do I feel like Googling on a fine sunny afternoon? Give Links!
https://dalmura.com.au/static/Magnatone%20vibrato%20design.pdf
https://www.tedweber.com/5h15-c-kt
https://www.tedweber.com/media/kits/5h15_schem.jpg
http://sluckeyamps.com/magnatone/magnatone.htm
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Well, I'm starting working on the circuit I want to create, and I'm looking at using part of the Hoffman ReVibe circuit and replacing the vibrato part of it with the Vibrato circuit from a Magnatone M10A. I'm attaching pdf files of those 2 circuits. I would be taking out the part of the circuit from Hoffman where it comes off the input signal going to the 12AX7 V1-B tube, and putting in the Varistor and Vibrato circuits from the M10A as shown on the attached pdf file, beginning with the first 12AU7 thru the 2 pairs of varistors in the circuit, including the vibrato section, but stopping before it goes into the Reverb part of the circuit. It would tie into Hoffman's reverb circuit at that point. How bad is this design? Thanks for your thoughts.
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If you don't want reverb, then jettison the revibe notions and build the M10 (or M9) circuit without channel #2 and without phase inverter and power amp. you don't need the full channel #1 preamp (two triodes/volume/tone), but you do want one gain triode (in M9 schematic, you don't need the 1st 1/2 7025, but you want the second 1/2 7025).
regardless of what Magnatone you use as a basis, you want to use the Magnatone oscillator circuit as-is. Bonham called this the VoPak (voltage package), the details of it are just as important as the details surrounding the varistors. You also want B+ voltages to be about the same as Magnatone B+ voltages ( +/- 10-15%).
http://magnatoneamps.com/schematics/magnatone_m9.jpg (http://magnatoneamps.com/schematics/magnatone_m9.jpg)
If you do want reverb., then I'd still jettison the revibe circuit and build the M10A with reverb (leaving off PI/power amp + channel #2).
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Thanks. That's a really good idea. I had started out months ago wanting a separate vibrato and reverb box to use with the Weber 5F1 Champ kit that I built, and then got into the Magnatone Vibrato which I really love, and was trying to figure out how to take a Weber 5H15 ReVibe kit, but use the Magnatone Vibrato circuit. I also really like the Fender reverbs. So that's how I got where I am. Do you know how the Magnatone Reverb in the M-9 or M-10 sound? I guess it depends a lot on the tank. I'm planning on using a 9AB3C1B for the long decay ability. I want it to be able to be really drippy wet if I choose. Thoughts? Thanks. Stephen
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I'm a bit confused by your suggestion in using the M10a circuit to leave off the PI/power amp part of the circuit. Could you clarify? I'd need to have a PT in the circuit to run the tubes wouldn't I? I couldn't run them off the OT could I? Also the reverb tank would be 8 ohms output so would the schematic for the M10A work okay with the tank. I've noticed in other schematics I've been looking at with reverb, that they are after the vibrato/tremolo circuit as usual, but have the OT feeding the signal into the reverb tank, and not paced at the end of the effect circuit before the output connection as the Magnatones do. Any reasoning behind either placement? Thanks.
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guessing;
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Yes, the output of the Magnatone would go to the input on the Champ, but I think he's talking about taking the power amp out of the Magnatone's circuit. It wouldn't need it to produce the power to push a speaker if it were being used as an amplifier, but it would still need to be able to heat up the tubes and push the signal through the circuit so that the signal can get to its output point, and then out to the 5F1 amplifier. I'm not sure what part of the power amp circuit he's talking about taking out of the schematic since it wouldn't be needed any longer to be able to put out a high volume, like 20 watts or more, which I think is what it's power level is designed to be, to push a speaker.
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taking the power amp out of the Magnatone's circuit
yup, that's the part that got overlaid :icon_biggrin:
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I'm a bit confused by your suggestion in using the M10a circuit to leave off the PI/power amp part of the circuit. Could you clarify? I'd need to have a PT in the circuit to run the tubes wouldn't I?
PI = Phase Inverter. And you are confusing power amp and power supply. You do not need a power amp. Yes, you need a PT which is part of the power supply.
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Sluckey - Thanks for your help. As a hobbyist I didn't recognize the distinction. So am I correct that you're saying that I don't need to have the Output Transformer (OT) and the Phase Inverter (PI) in the circuit? I know this may sound dumb, but why don't I need the OT in the circuit? I think other builds like the ReVibe has the OT in the circuit? Didn't you do a build similar to the ReVibe that also has the OT in the circuit? I apologize if I'm getting confused with all of these that I've been looking at. Thanks. Stephen
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why don't I need the OT in the circuit
"in the circuit"?, your 5F1 comes with OT, IF you want a revibe, then I goat cut up more :laugh:
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I'm a bit confused by your suggestion in using the M10a circuit to leave off the PI/power amp part of the circuit.
I said because you mentioned the weber Revibe kit and wrote this:
I want to have a separate vibrato/reverb
So I figured you wanted something like a Fender 6G15 where output is unity (or slightly less than unity). so, instead of a /PI+power amp+speaker out/ there would be an output jack. plug output jack into input of your amp (or any amp).
Are you wanting to build an effects box? or a full amp with onboard vibrato + reverb?
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Sorry to have confused folks. I'm looking to build a separate unit, like the Ted Weber or Hoffman "ReVibe", which is a "headunit" that is one box with the guts of the Fender 6G15 reverb unit and the Fender 6G12 tremolo unit, in one box. Its not designed to push speakers like a regular guitar amp. Its just for effects. Its like the ReVibe schematic shown above. Its like a transistor driven reverb/vibrato "stombox", except that its tube driven rather than solid state. The only difference from the above ReVibe circuit that I want, is to use the Magnatone true vibrato/varistor driven circuit in place of the "tremolo" circuit which is used in the Fender tremolo and ReVibe circuits. The output from the "Magnatone Revibe" box that I would build, would have a 1/4" phone jack input into which you plug a guitar, and would have for its output a 1/4" phone jack, which then gets plugged into the 5F1 Champ or any other guitar amp. As you can see in the Hoffman ReVibe schematic shown above, it uses an Output Transformer to drive the reverb circuit which then goes to the output as a jack, rather than going to speakers. It uses the OT to drive the reverb circuit rather than driving a speaker since the ReVibe doesn't need to have the power output to drive speakers at listening or performance level volumes. Hope this helps.
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sounds like it's color'n time, sharpen 'em up and draw it up or if you're a digital wonk, draft it up. :icon_biggrin:
all the stuff you listed is pretty complex, so go slow, submit your schematic for some extra eyes, once the schematic is sound, then develop the layout.
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Since this is my first try at something like this, can you recommend a simple, preferably free, software to use to design a circuit like this, and maybe test the circuit "virtually"? I also have learned that I don't need to use a reverb tank transformer like the OT that I've seen to drive the reverb tank, and that it can be done with a tube such as the 12AU7 thats shown in the M10A circuit. So I may be able to take the OT out of the circuit altogether. Thanks.
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maybe test the circuit "virtually"?
surf up threads on spice and it's cousin's.
If your only build is the 5F1 I would recommend the "kit" you're talking about or Dougs Revibe. Once it's working 100%, tweaking it to your flavor is easy pie
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You know, it may be that Terminalgs' first post with the comment: "If you do want reverb., then I'd still jettison the revibe circuit and build the M10A with reverb (leaving off PI/power amp + channel #2)." is really what I'm trying to do. And Shooter's response with the image superimposing the 5F1 output in the circuit is where I'm trying to wind up. What had me concerned is the use of the Output Transformer in the circuit. Now that I have learned that the reverb can be powered with the 12AU7 tube, and an OT isn't needed to power it, and the OT is not needed for the rest of the circuit because I'm not pushing a speaker, etc., this may be a relatively "simple" (famous last words) mode to the circuit. I'm trying to find out if I can find a Reverb Tank that will work with the tube circuit. Can anyone help me with figuring out the grounding on the one in the M10a circuit. Is the tank grounded on both input and output, or just output, etc.?
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The 4FB3A1B tank will work with the M10-A amp. AES sells it.
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Thanks for the lead.
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Silly rabbit asks silly question; Do you have the correct varistors or a source for them?
Here's an interesting read that may be helpful. https://dalmura.com.au/static/Magnatone%20vibrato%20design.pdf
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I've stitched together everything from the M10-A circuit you need to build your standalone reverb/vibrato project. This is an ambitious project. My M10-A is all true point to point wiring.
Should you decide to go forward I will be following with interest. It's a killer idea. You gonna have to do all the sweat work. I ain't doing a layout for this project! :icon_biggrin:
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Thanks. This is really helpful. What do you think of the reverb quality and which tank did you use? I've been reading pros/cons about tube driven tanks vs. output transformer driven ones and some say that the tube ones don't have a really "wet" sound-which is what I'm looking for. Now I've got to work on a BOM list which will be a pain, and decide where to order from. I'm thinking of getting the turret board from Hoffman and maybe modify it if necessary, but getting the chassis from Weber. I haven't been able to determine if Hoffman makes a chassis for their ReVibe that could be used for this project.
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SLuckey-One more question, what power transformer would be good for this project?
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Silly rabbit asks silly question; Do you have the correct varistors or a source for them?
Here's an interesting read that may be helpful. https://dalmura.com.au/static/Magnatone%20vibrato%20design.pdf
These will allegedly work for varistors: Metrosil 100-P/W/921 .
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Yes, I got a set of 2 pair of varistors. Thanks for the information though.
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250-0-250 @ 70mA and 6.3 @ 2A
https://www.hawkusa.com/manufacturers/hammond-mfg/power-products/power-chassis-mount-transformers/269jx
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Thanks.
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Sluckey, I don't see a rectifier or choke in the schematic for the M10 that you posted. Was that meant to be my choice, or something else?
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The rectifier is four 1N4007 diodes. There is no choke. That's exactly like the original. I'll link the original schematic in case you rather look at that. :l2:
https://el34world.com/charts/Schematics/files/Magnatone/Magnatone_m10a.pdf
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:icon_biggrin:
much better
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I'd recommend reading this thread if you haven't, spend time looking at the pic's, that's your "target", the words are kinda good to.
http://el34world.com/Forum/index.php?topic=25569.0
all the puzzle pieces are in the box, now it's the fun part, thinking about how, where, maybe why.
I like grided graph paper at this stage, resistor here, cap there, oops, erase.......
enjoy
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Shooter-thanks for the link. Really helpful article as I start down this road. Sluckey, is there any reason why a choke is not used in the Magnatone circuit vs. it being used in the ReVibe circuit? I'm thinking of using a chassis from Weber for its 5H15 ReVibe kit and also using its case as the housing. It looks like it will fit. I'm also wanting to use a turret board from Hoffman, and don't know whether I should just get the one he builds for his ReVibe or if I should try to do a custom one, or is there another board that would work? Thanks. Stephen
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Sluckey-In looking at the M-10 simplified schematic you provided, I wondered if I need to have (1) the bass and treble pots coming off the 12AX7's first 1/2 of the V1 tube, and the volume pot on the 2nd half of the tube--could I just go straight off pin 6 with the .047 cap (followed by a 470K to ground) and then into pin 2 on the 12AX7 V1; and (2) can I eliminate the tone boost circuit altogether and go from pin 1 on the 2nd half of the 12AX7 V1, then thru the .022 cap, and from there straight into pin 2 on the V5 12AU7, and eliminate the V3A 12AX7 altogether?
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Maybe I could use this preamp section from the Magnatone M2 circuit to give me a tone and volume control for the unit?
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Sluckey, is there any reason why a choke is not used in the Magnatone circuit vs. it being used in the ReVibe circuit?
Yes. Different designers.
I'm thinking of using a chassis from Weber for its 5H15 ReVibe kit and also using its case as the housing. It looks like it will fit. I'm also wanting to use a turret board from Hoffman, and don't know whether I should just get the one he builds for his ReVibe or if I should try to do a custom one, or is there another board that would work?
I doubt the circuit I provided will fit that weber chassis. I would not even try. Hoffman's revibe board will be useless for the circuit I provided.
You really should do a memory clear on all things associated with anybody's revibe. That circuit I provided is the shortest path to having your maggy vibrato and a good reverb circuit. It's a proven circuit. All the interfacing has already been done for you. All you gotta do is design a layout.
Maybe I could use this preamp section from the Magnatone M2 circuit to give me a tone and volume control for the unit?
You can certainly do that if you want a lame preamp. I have a M10-A and a M2. There is no comparison of the two, well maybe like a Yugo and a Mercedes.
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Thanks. I appreciate the candor.
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Sluckey-did you draw a layout diagram for your M-10A like you did for the M-2 that you would share?
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read all about it here 10 cents please :icon_biggrin:
http://sluckeyamps.com/magnatone/magnatone.htm
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Thanks. But I've been to that page. I'm trying to get an idea of what a layout on a eyelet or turret board would look like for Sluckey's modified 10-A that I'm working on and I'm trying to get an idea of the dimensions of the compacted schematic to see what size chassis I would need. I'd like to be using the one from Weber for their ReVibe and their case once I get a successful build, but don't know if what I want to build will fit.
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All my M10-A docs and info are on my web page. If I was going to build my proposed circuit I'd use a 17 x 6.5 x 2.5 chassis.
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+1
anything less you'll wind up where I did in my early learn'n days
even posting the results for a good laugh :laugh:
(It worked well, wound up making 4 or 5 amps from the parts after I gutted it :)
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Finally (you hope) is the only Audio taper pot the 100K for the Output Level, and the rest, ie. bass, treble, volume, reverb intensity, vibrato speed and vibrato intensity all Linear taper pots? Thanks again. Stephen
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All pots are audio (log) taper.
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Thanks again for your time, and patience. Stephen
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Sluckey-I"ve worked up my BOM for this project, and wanted to know if you could tell me the specs on the components. I'm assuming the resistors are 1/2 watt, metal film, except for the 1-470 wire wound, and the 1-3.3M 5% carbon film, and the 10W and 1 W resistors which I assume are cement film? As to the capacitors, other than the electrolytics, what do you recommend? What I thought I would do at this stage is to get the circuit components, and a perf type board, and lay out the components without soldering of course, to figure out the size of the layout and placement. I work better hands on rather than drawing it out. Then go from there. Thoughts? Thanks.
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My M10-A used CC resistors because that is what was commonly available during the '60s. If I were building this I would use 1/2W metal film resistors with the following exceptions...
470Ω WW for V1 pin 8... use 470Ω 2W metal oxide
5K/10W for V6 pin 1,6... use 5K/10W wire wound cement
2K/10W in power supply... use 2K/10W wire wound cement
1.5K/1W in power supply... use 1.5K 2W metal oxide
10K/1W in power supply... use 10K 2W metal oxide
10K/?W in power supply... use 10K 2W metal oxide
NOTE!!! All resistor values in the power supply are subject to change to achieve the voltages you need when using a different power transformer.
This is a complicated project. You will become frustrated very quickly trying to do what you suggest. I would never attempt to build it without making a layout drawing first. I use Visio and my components library has accurate sized components which makes layout much easier. Hoffman has a forum dedicated to a freeware program called DIY Layout Creator. Lot of people use that. The plus side of DIY Layout Creator is that you can give Hoffman a drawing and he will make a board for it.
Creating a workable layout from a schematic is probably the hardest and most time consuming part of a project. Much easier to work out problems and errors on the drawing board than on perf board. IMO it has to be done.
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Thanks again. What are your recommendations for the capcitors? I'll check out the DIY Layout Creator you mention. What is Visio?
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I like xicon caps and Illinois electrolytics. Visio is the program I used to make pretty schematics and layouts. Use google to tell more.
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Are they ceramic or film for the non-electrolytic ones?
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I don't know. Click on the capacitor link below this message and you tell me.
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Certainly plenty to choose from!! As to the software, since I'm an old retired fart with time to learn new things, and my brain is still pretty active, and I'm not traveling until we get rid of Covid-19, it might be a good project to learn the software and keep me distracted!! Thanks again. Stephen
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Certainly plenty to choose from!!
But only one xicon. I like them because they are cheap, small, and sturdy. Accidentally drag a hot soldering iron across it and it doesn't melt.
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to learn the software and keep me distracted
This seems to have a good following
http://el34world.com/Forum/index.php?board=26.0
Visio that others use is another
if you're into pain , I use Express PCB and express SCH
http://el34world.com/Forum/index.php?board=12.0
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I'll check them out. Thanks.
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Doug's .diy you've seen, Sluckeys and others Visio also.
express PCB, I started using when it came on 3.5" floppys :laugh:
there's no easy way to "display" it for show an tell, this is a screen grab so the component values ain't visable.
Pic a SW flavor, play maybe 20hrs and you'll have graduated from learning to doing :laugh:
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Thanks. I started working with Display today, and its pretty tedious. Since I've never built anything from scratch without a wiring layout, trying to figure out how to transfer the schematic to a wiring layout is tough. I can read the schematic fine, I understand the wiring concepts, its just trying to figure out how to "translate" it to the layout software. I'm pretty good with software and computers, I did .dbf "programming" in my spare time, and maintained the network and server and computers at my office--although that wasn't my job. So I've got to figure out a rhythm to it. Finding the part, putting it somewhere in the display, then adjusting the value, and then connecting the wiring is slow. I'm letting it rest a bit for today. Thanks for all your input. Stephen
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trying to figure out how to transfer the schematic to a wiring layout is tough.
yup
that's why my Revibe looked like it did, I wanted to build it, not think about it's looks :laugh:
"study" ANY of Dougs or Sluckeys drawings, bounce between the sch and lay, "grasp" the "why the hell did he do it like that?", after 2-3 honest days, the fog starts lifting, lights come on, and you see the shore :icon_biggrin:
Look at 1 tube at a time, don't try and swallow the entirety in one bite
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Thanks, I'll try to move cautiously, keeping my patience, and avoiding frustration!! Famous Last Words!
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avoiding frustration!!
that and the #42 are the answer :icon_biggrin:
when a hobby becomes a frustration, it's called work, It's also the main wormhole ALL gremlins use :evil5:
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Well, I'm starting to work on the schematic layout today. I decided to get an eyelet board the size of the one I hope will fit in the chassis I want to use. Its 15" long by 4" high. I've then put together a blank, paper turret board form printout from Doug's website on which I'm going to layout the schematic. I've printed out the Preamp section in 2 large blowup pages and have labeled the resistors and caps numerically, and then created an Excel spreadsheet with each of the part numbers for these components and their values. So my next step is to start tracing the circuit flow with component ID's onto the paper sheet turret board, and see how that works.
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printed out the Preamp section in 2 large blowup pages
Including the tubes and pots/jacks, like the pic below?
I've done nice layouts only to realize all the wires leaving the board become twisted like spaghetti. :think1:
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Nope, I'm just trying to get the components figured out right now, ie. the caps and resistors. It looks like I will need to use jumper wire to connect some of the turret lugs together for the circuit to be "compact". What wire do you use for that? Something like 20 ga. solid core insulated wire?
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I use 22awg or 24awg tinned solid copper.
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I'm an odd nut, I like 22ga stranded for everything but filaments. 20ga solid is fine, just more prone to nicks and hard bends that break over time.
the caps and resistors
how many is fine, where on the board requires thought for where they go off board.
an example would be the 1st turret is typically pin 3 V1a, NOT pin 1 because of tube rotation for filament wiring
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I'm an odd nut, I like 22ga stranded for everything but filaments. 20ga solid is fine, just more prone to nicks and hard bends that break over time.
He's asking about lacing turrets and jumpers on the board.
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I like the 22 gauge solid core wire. I like the solid core because it stays where you put it. I recently purchased some of the push-back cloth wire that Doug sells. It's flexible and the cloth is easy to push back. I look forward to using this wire.
For the heaters I like 18 gauge solid core. I keep the twists down to about 1 twist per inch to avoid stress cracking the wire. I saw a chart somewhere that provided the minimum bending radii for various solid wire gauges. One twist per inch is sufficient to keep heaters quiet in my experience.
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Well, I've gone back to the DIY Layout program, and am starting to get the hang of it. I'm attaching a copy of the DIY so far that is 1/2 of the PreAmp circuit. So I"m attaching the DIY file and the pdf of the Pre-Amp. I've completed page 1 of the 2 pages. So I thought I would send it up for your comments. I'm sure you'll be frank, but its my first time--so please be gentle!!
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gotta look at the original but c1 n R3 "look" wrong EDIT: I'm wrong :think1:
lacing turrets
:laugh:
bite of a pain to strip, even kinked 'em :icon_biggrin:
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Your turret board looks really nice. What wire did you use to join the turrets together, I guess you would call it "jumper wire" of a sorts? Also, what circuit is it for? Thanks. Stephen
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typically called "lacing" and the wire I used is NOT something I'd recommend for lacing, it's a Teflon based, hard to get stripped, and pricey.
any solid strand copper, solder coated copper works, I used pvc solid I got from radio shacks end of days sale, easy to strip, almost free, but it's all gone so........
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What was the build?
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http://el34world.com/Forum/index.php?topic=25104.0
Version II is in my brain, but that's not waking up fast any more :icon_biggrin:
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I got the Preamp wiring section completed in DIYLayout this morning and the file is attached. I've color-coded the wires so that helps a bit, but it still seems like there's too many wires running around. I did modify the placement of some of the components from the first 1/2 of the build of the preamp section that I did yesterday, to make it look like its flowing a little better. One question I have relates to wiring of multiple components at 1 turret or eyelet connection. If you look at the schematic that I sent up yesterday that I'm working from, is the way I wired it at the C10, R16, and R17 connection point, and also at the C9, R15 and R16 connection point ok? I didn't know if its okay to wire them at the related points, ie. is it better or is it necessary to wire to 1 point, then wire from that point to another, etc. My thinking is that if the ends of those components are all going to wind up at GND, then I could put them all together at 1 point, and then run a wire from that point to GND. Is that okay? I did the same thing to get C9 to GND by taking the GND lead to the point where it meets with C8 and R12 which then goes off to GND. Thanks for your education. Stephen
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Does .diy allow for export to something "common" like .jpg ?
multiple parts at one point is "normal" as long as "that point" makes sense.
you wouldn't want "that point" having a "fly wire" across 80% of the board to another point, when it could be re-done so the fly wire becomes a jumper to the next eyelet over. (hope that made sense :)
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I can export it as a pdf, and I've attached the file, but it only exports stuff on the board, and not off the board. I don't know if this helps. You could download the DIY program for free and use that if you want.
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what you posted is fine, I've already forgot way more programs than I want to learn :icon_biggrin:
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Sluckey--what is the wattage of the 10K resistor between the D and E caps? Is it 1 Watt also?
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Unspecified on the original schematic. That usually means 1/2W. I'd use a 1W though just to be sure.
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Thanks. Here's the PreAmp and Power Supply Board.
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Sorry, and here's the PS with Component ID's.
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Have you seen this on grounding?
Very helpful for new builds.
http://www.valvewizard.co.uk/Grounding.html
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Great! Thanks. Stephen
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I've been making some progress with converting the schematic to a layout using DIYLayout software, and I"m attaching the latest. I've got all the components for the Preamp, Power Supply and Vibrato sections on the layout, and will have just the Reverb to Output remaining. Its going pretty well, but it seems like I"ve got a lot of hook up wires on the board, and most of them are going to grounds. I guess I'll try to clean that up once I get the circuit completed. Any ideas are appreciated. Stephen
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most of them are going to grounds
consider a ground buss for the preamp stuff. I've stole from Sluckey and Doug and have 2 parallel busses, ground on one side of board, power on opposite side.
all the "pot" grounds can be done at the pots, then 1 wire to board buss.
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I have pretty much finished up the layout this morning, it still needs some cleaning up for the hookup wiring to be a little neater and maybe more efficiently routed, but I guess my next stage is figuring out whether to use a turret or eyelet board, or something else on which to mount the components. I've not worked with turret boards before, but they do look neat--in more than 1 one way. I'm just not sure of whether to get a turret board with the correct dimensions that I need and with all the turret holes filled in, or try to customize the layout of the turrets. Thoughts on options and methodology? Thanks. Stephen
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Sluckey and Shooter, I wondered what you use for jumper wire between the components on the turret board. I looked at the Layout image that Sluckey did of his Custom M-2 and can't really tell. Is it insulated? Thanks. Stephen
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I use 24 AWG bare tinned copper wire. Single strand. This pic shows it very well...
http://sluckeyamps.com/lil_maggie/m_big.jpg
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That's a really great looking build. I finished the DIY layout of components, and it fits on a 15" board, but its certainly not neat looking--yet. I was able to upload it to Hoffman's Analyzer for a turret board build just to see what the board would look like, and it produced an image based on my layout. But my lingering question is whether or not the components will physically fit the way I've got them laid out. For example, in one section of my layout I have 3, 1/2 watt resistors and 1 capacitor connecting end to end vertically on the board, within the 3.5" boundary. But I don't know if they will actually fit that way. How do you go about figuring out where you want the turrets to be placed? Do I need to go into the "properties" of each component, and put in its dimensions? Other than measuring each one, is there some other way to do that? Thanks again. Stephen
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Sluckey--what are the dimensions of your turret board? That is the Custom M-2 isn't it? Stephen
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Sluckey- Is it the Positive + side of the 1uf, 450 V electrolytic cap at V6 that's going to the B cap?
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Sluckey- Is it the Positive + side of the 1uf, 450 V electrolytic cap at V6 that's going to the B cap?
Positive side connects to V6 plates, not the B cap.
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Yes, sorry I just meant it was on the lead where the 5K 10W connects from the plate to the B cap. And what is the size of your turret board for your build?
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And what is the size of your turret board for your build?
Which build?
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Sorry, the one in the photo which you recently attached. I think it is the Custom Mag 2. Its this photo: http://sluckeyamps.com/lil_maggie/m_big.jpg
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The size for all my boards is in the documents pdf. Won't be helpful for your project.
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I was thinking of using a single stereo jack for the Vibrato/Reverb footswitch jack, and use a 2 button Fender type footswitch. Thoughts? Anything special on the wiring from the jack to the board points? I've seen a shielded 2 wire plus ground cable that has 1 shielded and 1 unshielded wire, plus the ground. Hoffman used to carry it but apparently doesn't anymore.
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should work, I like a 3 wire shielded, or 2wire (one shielded) whole cable shielded.
outer shield is NOT for signal/power/ etc. so you need 2 signals, a ground, everybody shielded.
for work I was a frequent flyer of both belkin and belden :icon_biggrin:
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I was thinking of using a single stereo jack for the Vibrato/Reverb footswitch jack, and use a 2 button Fender type footswitch. Thoughts? Anything special on the wiring from the jack to the board points?
Saves drilling one hole. If the FS jack is very far from the point of connection for the reverb then use standard single conductor shielded cable. ( The orig. M10-A has the FS jack mounted next to the Reverb pot so only a 2" unshielded jumper was needed). The Vibrato doesn't need to be shielded.
You can buy a Fender footswitch for $25, and cut the RCA phono plugs off to install a stereo 1/4" phone plug. I would prefer to just put two phono jacks on the chassis.
https://www.tubesandmore.com/products/footswitch-box-fender-two-button-vintage-rca-plugs
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Thanks. I'm also trying to figure out a way of maybe limiting the number of pot cutouts in the chassis and was wondering if there's a "dual" type pot I could use for maybe the bass/treble pots which are both 1 M audio log, and maybe another dual one somewhere else. I've seen a dual pot on AES, but don't think that it would work since it only has a single shaft. I would need something with 2 wipers and 2 "controllers". I have a MacIntosh Integrated Amp that has that type of setup for some of its controls. Ideas?
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They're called dual concentric pots. You also need dual concentric knobs. Maybe you just need to build the simpler M4?
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I'm trying to adjust my layout to make the components flow a little better with fewer jumpers, and I have a question about a connection in the attached schematic. If you look at the attached part of the circuit where the Vibrato section is starting on the V5 tube, Pins 3 and 8 from the cathodes show their 47K resistors R-24 and R-30 connecting on their GND sides which leads to GND from R-24. Is there any reason I couldn't run them separately to GND, maybe even different GND points, or do they need to connect and then go to GND?
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Now this is more of an issue of layout image. Attached is a pdf of my layout without the hookup wires showing. I took them off just so I could better see how the components lineup. I'm 95% sure that the components on the circuit are properly connected, and of course before I start assembling anything I'll recheck all the connections 2-3 more times. My question is whether you see anything about the layout itself that I should strive to change. The images that Sluckey and Shooter have posted of their projects show all the components on the board running parallel to each other in nice, neat rows, and mine seem to go all over the place. I guess it doesn't matter if its not an issue electronically, but would appreciate your comment. Thanks.
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I'm trying to adjust my layout to make the components flow a little better with fewer jumpers, and I have a question about a connection in the attached schematic. If you look at the attached part of the circuit where the Vibrato section is starting on the V5 tube, Pins 3 and 8 from the cathodes show their 47K resistors R-24 and R-30 connecting on their GND sides which leads to GND from R-24. Is there any reason I couldn't run them separately to GND, maybe even different GND points, or do they need to connect and then go to GND?
All that's important is that each resistor connects to ground. I don't see any attachment?
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Let me try the attachment again.
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I predict a lot of trouble with that layout. Nothing is drawn to scale. Actual components will likely not fit. It looks like you just stuck a bunch of components on the board without any consideration for signal flow. Getting a good workable layout from a schematic is probably the hardest and most important phase of a complicated project such as this. Study some of Hoffman's layouts as well as some of mine. Our styles are slightly different but both follow good proven guidelines.
I suggest something similar to the attached layout of the preamp only. (Ran out of steam before getting to the effects). This layout is drawn full scale. Components will fit. For example, here's a pic that shows a board layout and an actual board. Pretty close match...
http://sluckeyamps.com/supro/board.jpg
And here's the partial layout for your project that I started. Might help you get your layout more logical and practical.
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Thanks Sluckey-I really appreciate all your help. Yes, I started with the schematic, and the board dimensions that I want to use if possible, then started with the DIY program, and just added the components as I read through the schematic starting with the input jack. So this will give me a fresh lead on getting going. I appreciate your time. Stephen
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Sluckey-I was looking at the 2 layouts you made for me, and was thinking of deleting the tone boost part of the circuit, since this is not really going to serve as an amp for me. In looking at the layout without the tone boost circuit in it, am I correct that I eliminate the V3 tube altogether and go from Pin 6 on V1 to Pin 2 (grid) on V5, and not Pin 1 (plate) on V5 as you have shown on the layout?
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In looking at the layout without the tone boost circuit in it, am I correct that I eliminate the V3 tube altogether and go from Pin 6 on V1 to Pin 2 (grid) on V5, and not Pin 1 (plate) on V5 as you have shown on the layout?
You are correct. I made an error on the drawing. I'll see about correcting that.
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Well I've been working on a revised layout with the helpful start from Sluckey, and I've attached it for comments. It covers the preamp and vibrato stages. The vibrato circuit is the toughest part of the layout for me so far, and hopefully I've got it all wired as the original schematic. I decided to leave out the Tone Boost part of the circuit since this is going to be an effects box and not an amp.
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VR1, VR3, and VR4 are shorted, ie, both ends are connected together. I didn't look at the rest of the layout after seeing that.
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Thanks for the catch on the Varistor shorts Sluckey. I'll check it out. I understand what Greenwichpaul is saying. Being grumpy is not necessarily a bad thing. I'm an old, grumpy retired lawyer, and having done commercial litigation for a long time, I'm used to being surprised by "clients" and spending a long time trying to solve problems. That's what makes this project/client interesting for me--even if it may have a lot of land mines waiting for me. Sometimes you win, sometimes you lose, and a lot of the times you compromise. Thanks to everyone for their input. Stephen
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grumpy old men try to scare new builders off
:icon_biggrin:
I've been teched in pubic, private, corporate, and Military schools, the grumpy cranky teachers that won't hold your hand, make you use your own brain, tell you to read the F*ckin book, are hands down the best of best!
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I've looked at my layout again, and don't see the short connection where V1, V3 and V4 are tied together. I've moved the turrets a little bit in the attached image to better show the connections, but this is how I put them together. Maybe this updated pdf is better. My read of the schematic is that the front ends of V1 and V2 connect to each other, as well as the front ends of V3 and V4. The back ends of V1 and V2 connect together through two .047uf caps, and the same for the back ends of V3 and V4. Then the back ends of V1 and V3 connect together through two 100K resistors, and the same thing for V2 and V4. I apologize if I'm being dense on this. Thanks. Stephen
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> don't see the short connection where V1, V3 and V4 are tied together
"V" = "VR"??
I see VR1 and VR4 shorted. What am I mis-reading?
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PRR-Thanks, I've probably been looking at this toooooo long. Yes "V" = "VR". I understand what I did, and that it created the short, but don't know "why" I made the mistake. I'm going through the circuit again, and hope there's nothing else that I screwed up. If you see anything else in the updated file that I've attached, that you want to pass on for me, that would be great. I appreciate your help. Stephen
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(and sorry, it always irritates me when grumpy old men try to scare new builders off, I'd like to see this build work, but I'm a science teacher and I'm concerned you need a bit more scaffolding on this project!)
Do I irritate you? Seems I've done more to encourage this project than anyone participating in this thread.
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Sluckey, no not at all. You don't irritate me at all. I feel you're being helpful. I'm someone with a hobbyist skill level, and it seems like everyone else is much more experienced, so I appreciate the input. That's why I came to this forum with this project. I want this project to work when its finished, and if I'm missing something because I'm inexperienced I honestly want to know so I can learn from my mistakes. Stephen
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I'm still working with your layout that you made for me, and I'm using the one without the boost circuit in it. One thing I've done was to add a .022 coupling cap coming off of the 220K resistor coming off the plate of V1, and then connecting that cap from the plate on V1 to the grid pin 2 on V5. I hope that was correct.
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Sluckey, no not at all. You don't irritate me at all.
I've never felt that from you. My question was directed to greenwichpaul in response to his statement.
then connecting that cap from the plate on V1 to the grid pin 2 on V5. I hope that was correct.
No. Remove the cap. Put the wire back. A direct connection is required.
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Thanks. Can I ask why you don't need a coupling cap in this instance to connect the plate from V1 to the grid on V5?
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That's a good question.
V5 is a cathodyne phase splitter. By design, it's cathode will have a large dc voltage on it. This means the grid will also need a large dc voltage that will be just a bit less than the cathode. This is necessary for proper biasing of V5. The direct coupling from the plate of the previous stage is the easiest way to obtain the large dc voltage for the grid without having to use any components for bias. The Magnatone engineers decided to use the direct coupled cathodyne.
You can use an AC coupled cathodyne by using a coupling cap, but now you have to get the high dc voltage for the grid by some other means. You could use a fixed bias circuit which requires a 2 resistor voltage divider from a B+ source, or you could bootstrap to the cathode, which also requires 2 resistors.
When you run across stuff like this that doesn't make sense to you, please ask. Sometimes there is a logical answer. Other times it may just be an error in the schematic/layout (like my last drawing :embarrassed: )
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+1
for a little deeper read (that I keep going back to over and over..:)
near the bottom you'll find the DC coupled version.
http://www.valvewizard.co.uk/cathodyne.html
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Wow Sluckey! Obviously way over my head. At this point in my education I had thought a coupling cap was needed in order to get the AC Signal passed on to the next tube/section of the amp, and if you didn't use a coupling cap the DC would pass through instead and would mess up the signal. So that's why I assumed a cap was needed to get the signal from V1 to V5. I'll read the article that shooter attached. Thanks.
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Sluckey, I've finished the section of the vibrato where the signal leaves the varistors and is headed to the tremolo section for V6, but I need to do the V4 wiring to complete the vibrato. As to layout, should I just continue with the vibrato circuit in the layout until it is completed, or wire the reverb layout next and put the V4 section of the vibrato circuit at the end of the layout. I'm assuming that it would be better to finish up the vibrato circuit, and then move on to the balance even though the schematic shows the V4 section pushed off to the side.
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I would put V6 and V7 next to V5. And put V4 at the end of the line.
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(and sorry, it always irritates me when grumpy old men try to scare new builders off, I'd like to see this build work, but I'm a science teacher and I'm concerned you need a bit more scaffolding on this project!)
Do I irritate you? Seems I've done more to encourage this project than anyone participating in this thread.
Not at all. You're amazing, I'm constantly impressed by how helpful you are. Sorry if I sounded patronising to the OP, I was trying to be helpful as I have suffered from being over-ambitious.
(and btw grumpy old men is referring to me... and also a german amp forum where you can get told off for asking naive questions. )
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(and sorry, it always irritates me when grumpy old men try to scare new builders off, I'd like to see this build work, but I'm a science teacher and I'm concerned you need a bit more scaffolding on this project!)
Do I irritate you? Seems I've done more to encourage this project than anyone participating in this thread.
Not at all. You're amazing, I'm constantly impressed by how helpful you are. Sorry if I sounded patronising to the OP, I was trying to be helpful as I have suffered from being over-ambitious.
(and btw grumpy old men is referring to me... and also a german amp forum where you can get told off for asking naive questions. )
So how the hell is that comment even related to this thread? If you aint got anything nice (or helpful) to say why say anything at all?
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> if you didn't use a coupling cap the DC would pass through instead and would mess up the signal.
Well, usually.
"MOST" tube stages set the grid near zero V with a large resistor, stand the cathode up a few volts with a resistor, and a plate resistor set the plate at 40% to 70% of B+.
BUT there are cathode followers. The idealistic CF has plate at full B+, grid at half of B+, and cathode "following" grid a bit above half B+. For 300V B+ we want a source of 150V bias.
And then there is the Cathodyne which has equal resistors in both plate and cathode. The idealistic grid bias here looks like 1/4 of B+, putting 1/4 of B+ on cathode and 1/4 of B+ across plate resistor (plate sits near 3/4 of B+). For 300V B+ we want a source of 75V bias.
If the stage before this stage has its output at appropriate voltage, or we can cleverly contrive a good voltage without much performance sacrifice, why not omit a cap and direct connect it?
There's reasons not to. But usually, if you are not sure (or off the edge of your scaffolding), go with what is on the plan.
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I've done some more work on the layout and the updated pdf is attached, and in this work I have added 1/2 of the Vibrato circuit, the Reverb to Output circuit, and the Power Supply part of the circuit. Once this layout is resolved, then I just have the last 1/2 of the Vibrato to layout. There are 2 areas that I would like to ask for special input on. First, and perhaps easiest, I used the ground on the RCA Reverb Input jack as a point to connect several grounds to, primarily for convenience based upon the way things are laid out currently. Any issues/concerns with that? Second, and more of concern for me, is the power wiring for D and E on the board. Have I got that correct? It was hard for me to think "in reverse", ie. going from the end of the power supply to the beginning. The resistors and caps in that part of the circuit were making me dizzy! So once again, thanks for your help. Stephen
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fwiw;
take a look at my board example Pg 2 reply #68. putting the filter caps closer to where they do work is a better approach, usually :laugh:
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Second, and more of concern for me, is the power wiring for D and E on the board. Have I got that correct?
No you don't. You have D and E shorted together! Remove that jumper. And the long wire that you have connected to E does not go to V7-1. It only goes to that 270K resistor on the left end of the board. Then the other side of that 270K goes to V7-1.
I had to stop looking at that point. :cry:
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Thanks Sluckey- I was trying to figure out how to get B+ from D to E, and didn't realize that the B+ feed for E could come from the 10K resistor off of D. I re-checked the B+ feed for C on the V7, and it looks correct to me-for what that's worth (Ha Ha). Whenever you get a chance, let me know if you see any other "issues"! Thanks. Stephen
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Shooter, thanks for reference to the Silvertone layout. I put the caps where I did because I thought I needed to isolate all of them from the preamp part of the circuit. Does it matter in a build like this one where this is an effects box and not an amplifier, or is my assumption incorrect? Thanks. Stephen
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Does it matter in a build like this
I'm ripping off my garage roof so i'll hunt down your schematics later;
typically I put the caps where the "taps" are, so if V1 gets "tap D", I try and put cap close to V1. (That "assumes" you still don't have to fly a 12' ground wire)
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I re-checked the B+ feed for C on the V7, and it looks correct to me-for what that's worth (Ha Ha).
I never said anything about that. I said, "... the long wire that you have connected to E does not go to V7-1."
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If you are looking to simplify your build, get rid of the 1st gain stage and tone stack. you said you want this to be effectively a vibe stomp box (maybe to sit on top of your amp)., three control knobs needed: speed, intensity, level(volume).
you do need some gain before the effect so there is one gain stage (you don't need two), and you can reduce it with the level pot right before the output jack. See attached.
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Sluckey, I was just commenting about the other B+ connection for C on V7. I understood what you were saying about the short and the mis-wiring to Pin 1. Thanks. Stephen
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Terminalgs, thanks for the info and the layout. I'll probably continue as is since I think I've gotten through most of the layout. But I'm going to keep this as an option if I get into trouble with the build.
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if I get into trouble with the build.
:laugh: That's why we do this design stuff with computers n paper, to avoid trouble, mayhem, and gremlins during the build :icon_biggrin:
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I was wondering if someone would be willing to educate me a little bit on some theory. The schematic that Sluckey provided and from which I'm working, shows the Power Transformer connecting to a rectifier and then out to the capacitors. I think the transformer that is being used has an initial output voltage of 250 VAC at the secondary windings. Then it goes through the reciifier and at Cap A it's voltage is 410 VDC, and at B it's 338 VDC and gradually decreases as it goes through the caps. I'd like to understand what is happening that boosts the voltage initially and then gradually decreases, and how do you calculate the voltages you want in a circuit like this. I assume it has something to do with the value of the caps that are used and the resistors, but if anyone could give me a simple explanation, it would be appreciated. Thanks. Stephen
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Read this...
http://www.valvewizard.co.uk/
Scroll down to the power supply section where you will find several links to everything you need to know about power supplies. Easy reading.
PS... My PT puts out 290-0-290VAC. 290 x 1.414 = 410VDC.
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Thanks, I’ll check it out.
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I read the article on the power supplies, but I guess a better way to phrase my question is "how do you know what DC voltage you need for a particular circuit and for the different parts of the circuit?" In other words how did the Magnatone designer determine that for this M10 circuit there needed to be 410 volts at A, and 338 at B cap, etc., and then secondly how do you know what sized resistor to put between the caps to reduce the voltage to what's needed at that point?
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it's NOT an easy explanation;
what I've learned, start with the output, work to the input.
so;
I want a 20W amp
I want to use PP 6L6
I get tube datasheet, find ALL the cool data, look up OT, walla, I need 350vdc at plate
I go to PT, deside type of rectification, filtering, ohms law for series Resistors, boom tap A is 350vdc.
I need to drive the tubes...........
I need to provide a killer preamp sound to drive the driver.......
I give up, steal from everyone else that did the hard work, put it together and rock out :icon_biggrin:
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I give up, steal from everyone else that did the hard work, put it together and rock out :icon_biggrin:
:l2:
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Sluckey-I'm finishing up the layout, and was working on the Power Supply section, and noticed that B+ A no longer has a connection in the revised circuit you sent me and that I'm working from. Looks like it originally powered the OT. So, is there any need to have the first A Cap 40uf 450 V in the circuit at all anymore? Could I just take it out, then I'd be starting with the B+ B cap. Thanks. Stephen
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Node A is not used since there is no power amp, but it is still necessary to provide the smooth dc voltages needed by the other circuits. Don't take it out.
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was typing anyway :laugh:
is there any need to have the first A Cap
fwiw;
a lot of times, especially in SE or small signal builds, I put a cap/resistor filter "up front"
typically that takes the AC "ripple" from 2vac to <1vac on the backside (Tap B)
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Thanks to both of you guys. I just wanted to make sure that I hadn't missed something, or that it would be okay just leaving it in the circuit. If it were taken out, then in order to get the voltages down to the level needed coming out of B+ B cap, wouldn't you need to increase the resistor between B and C?
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DON'T TAKE IT OUT!
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Believe me I wasn't going to do that! But I was curious about what the effect would be on the circuit. Seems like the DCV at B would be much too high and it would need to be reduced somehow.
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Filter caps don't drop voltage. They just smooth it. Go read that power supply link again.
There is a good chance that you may have to juggle the resistor value between Node A and Node B. The missing load of the PA will cause all the voltages to rise. But that's assuming you will use the exact same PT as in the orig M10A. I seriously doubt that! It's unlikely but the PT you choose may already give you 'perfect' voltages. This is not something to worry about but plan to change a resistor (or two) in the PS rail. IOW, make sure your layout will provide easy access to the power supply resistors.
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fwiw;
this is one of the better finds for WHY answers, It'll make studying for the boards seem easy :icon_biggrin:
http://www.aikenamps.com/index.php/white-papers
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Thanks again to both of you. Stephen
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For those sections of the layout where there are several components in a row leading to ground, such as in the Vibrato speed/intensity section, is it ok to jumper them together as in a daisy-chain and then lead off to ground from the last one in the chain--as opposed to connecting each one to GND separately?
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yes
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Sluckey, in your Reply #87 you attached this photo http://sluckeyamps.com/lil_maggie/m_big.jpg . Do you have a photo of the underside of the board so I can see how the hookup wiring looks? Or another build that you did? My DIY Layout drawing has a lot of wires coming out of it and it just looks messy. I'm trying to neaten it up, etc. Thanks.
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you have a lot of tubes, so more wires.
look at one of Dougs turret boards for an AB763, something like twin reverb layout.
this is a simple 3 tube, the blue wires are jumpers, the layout keeps parts for each tube "close" to the tube. When I build it, the jumpers will be on top, as a service guy, I hate the extra work of "looking" under the board :icon_biggrin:
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I notice that in the layouts that both of you have provided, in most instances you've got the components running vertical and parallel to each other, and that you connect them where needed with horizontal jumper wire. But there are times when no jumper is used, and the components are connected at an angle to each other at the turret, sometimes like a V junction. Is there any reason why you don't use the jumpers sometimes and just connect the components directly at the turret and lose the parallel scheme? Is this just an appearance sort of thing?
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There are two pics on this link that deal with my underboard jumpers. I highly recommend doing them this way. Look closely at the way the jumper is inserted thru the bottom of the turret and hooked over the top of the turret. My jumpers will not accidentally fall out when soldering other components. Jumper wires are 24AWG solid tinned copper. I stripped insulation from 22AWG teflon wire to slip over the jumpers when they need to be insulated.
http://sluckeyamps.com/VAC15/ac15.htm
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I notice that in the layouts that both of you have provided, in most instances you've got the components running vertical and parallel to each other, and that you connect them where needed with horizontal jumper wire. But there are times when no jumper is used, and the components are connected at an angle to each other at the turret, sometimes like a V junction. Is there any reason why you don't use the jumpers sometimes and just connect the components directly at the turret and lose the parallel scheme? Is this just an appearance sort of thing?
It's just my style. I prefer parallel components but some times you just need a "V" or "birds foot" for neatness or to be compact.
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Great photos from your build. Its really helpful to see how it was assembled in stages.
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Well I finished this layout, and am attaching 2 files and ask you to take a look. The main issue I'd like some input on is whether the layout looks like it will hold the components ok or if things are too close together. I've attached the DIY layout and the Hoffman Turret analyzed layout for a turret board. I printed out the Turret board to scale and everything fits, I just don't know if the turrets are too close together. The board is 15.125" x 3.125". As far as the circuit is concerned, I'm going to go over it a couple more times to make sure its correct, and at this stage it would be appreciated if there's anything that jumps out at you that is a wiring problem--sort of like before. I appreciate your time and help. Thanks. Stephen
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can you post the schematic, and your .diy file ?
thanks
dave
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Sure. Its attached. Stephen
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HA, I have an older version
suggestion, delete the power wires going back to the caps, they're called out at both ends. that cleans up the clutter some. If you "need" them edit selection to dots, I use dashes for under board.
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Thanks, I've attached a pdf with the power wires removed. Do you have any thoughts on whether the turret spacing will work or if they are too close together and would cause difficulty in mounting the caps and resistors, etc.?
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Turrets look too close to me, but without a scale reference I can't really say. Ask Doug. He'll know.
I use a 5/16" grid to space turrets on my boards. The only deviation was the AC-15 board which uses a 1/4" grid.
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turret spacing
did you use Doug's turrets from this common parts file?
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Yes, I used the larger one that has a .1" hole and .2" size specification. Since I've not done or actually seen any turrets before, I don't know what to consider. Do you know if he builds boards using either size? You know I just realized that the larger one is an "eyelet", and the smaller one is a "turret". That would make a difference! Do you know if there's a way to do a global replace in the DIY software so I don't have to go to each turret and change it? Thanks again.
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Sluckey, so are you saying that if the turret fits within the boundaries of the 5/16" or 1/4" grid outline, then they will work okay for mounting components being right next to each other without needing any additional space between?
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I just realized
yep, did that for a couple, then switched to turrets that Doug made.
I haven't been able to figure out how to "put a box around" (select) a group of components so I can move them as one. can't "select all" turrets either.
gonna upgrade to latest version n play some today, it's artic freeze coming here!!!
EDIT:
fwiw
played with shift n ctrl keys, figured out if you click a turret, component, etc, then hold ctrl and click a second object, they both "highlight", then you can delete, move as a group. looks like you can do it with as many objects as you want, didn't figure out how to "replace with"
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What I just tried and worked a few minutes ago is to go into Connectivity section on the left, click on Turret, then right click, Select All. That then highlights all the turrets, then right click on one of the highlighted turrets, click Edit Selection, and then make the changes, and save. Seems to work.
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AH, thanks
click on Turret
was that "Doug's" or the Diy one?, I think there's a size difference, but haven't double-checked.
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I think it was Doug's. There is one for turrets and another one for eyelets. I think maybe the turret is one of his that got added to DIY.
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Sluckey, so are you saying that if the turret fits within the boundaries of the 5/16" or 1/4" grid outline, then they will work okay for mounting components being right next to each other without needing any additional space between?
That's not what I'm saying. I set up a 1/4" grid. Then place my turrets centered on the cross-hairs of the grid, not inside the grid squares. My turrets have cross-hairs on them too and this makes it easy to "snap" the turrets to the grid cross-hairs.
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Gotcha! I'm trying to re-do my layout in DIYLC but can't figure out how to make a global change. Would like to avoid having to re-do each one of them. But I'll keep working on it-there ought to be a way.
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I was watching one of Doug Hoffman's videos on the DIYLC software and he was talking about the turrets and connecting components to them. He said that the hole on the top of the turret is very small and its hard to get more than 1 wire in them from the top. He talked about attaching them by hooking to the sides, but was stressing the point of using turrets to connect jumpers. My concern is that I've got quite a few connection points with 3-4 wires meeting and wanted to ask if that's going to be a problem for me when I hopefully get to the point of wiring the board.
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3-4 wires meeting
everyone has "their" flavor, mine, more than 3, I add a 2nd turret n jumper
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Thanks.
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I've gone through the Layout and fixed a couple of my misses, and think everything is now right. I wanted to ask though if you would mind taking a look at the attached schematic which is the Vibrato control section, and see if my corresponding section on the attached DIY file is correct. It starts in my Layout in the area to the left of the C cap lead to the board.
I also had a question about the type of Pot for the Vibrato Speed. I've seen RA type pots used on some circuits and didn't know if there's a reason Sluckey why I don't need that type for this build. I think you said earlier in this saga that all of the pots are Audio Log. Thanks. Stephen
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I'm not allowed to operate heavy equipment, so......
there's a red-ish wire exiting lower left, the other end doesn't go where you have it.
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giving up in the circle, going to paint :laugh:
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You're right. I guess I was tired and missed it. I think I've got it wired correctly now for the B cap power supply source going to plate 6 of the 12DW7. I also moved the secondary power source supply going from the C cap, and now it runs from the C cap connection at the 10K on the layout to the other C supply on the 270K.
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look inside the circled area AND the schematic, there are 2 330K resistors that come together, ONE .0047uF connects there and goes to ground.
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Got it. I moved the jumper that connects at the bottom on the 330K on the left and goes to the top of the 330K on the right, down to the bottom side of the 330K on the right, where it meets with the .0047uf.
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I was going to build myself a Revibe, but with the Magnatone vibrato instead of the Fender trem, just like what you are doing. I have enough genuine Magnatone varistors to do it, and enough knowledge to work through what needs to change in the circuit to do it, but I haven't had the time to do it. :) So you might end up getting yours done first. It is an interesting project and I'm eager to see how it turns out wsscott!
Greg
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Yes, I'm excited to hopefully get to the assembly part of this project soon. I still keep going back over my Layout. I've never done a Layout before and its really tedious for me with this circuit. I don't have much experience overalll. The only amp I built was the Weber 5F1 kit, but it did work the first time I plugged it in--and its still working. So I feel if I can get the circuit correctly laid out, then I can build it. I was going to do the same thing as you by modifying one of the Weber Revibe versions with the Magnatone vibrato, but I was convinced by this forum that it would be better to take the Magnatone M10a circuit, and simplify it by eliminating the second channel, and I also decided to eliminate the tone boost circuit since it already has bass and treble controls, plus its not being built as a stand alone amp. I want to use the Weber cabinet for the 5H15 Revibe, so that limits my chassis size to 15.5". But by simplyfying the circuit it looks like it will fit on a 15.125" turret board. However the Weber chassis won't work because of the cutouts, and CJ at Weber says they don't make custom chassis'. But I have found a company that does one off's with aluminum for about $50, so that should work fine. I'm going to get a blank chassis and drill the holes. The Hammond PT that I'm going to use doesn't need a cutout. So stay tuned.
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Am I correct that the plates, grids and cathodes on the V6 12AU7 tube are bridged with each other, ie. the 2 plates are bridged with each other, the 2 grids are bridged with each other, and the 2 cathodes are bridged with each other? If so, can I ask why?
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That's correct. It takes a lot of current to drive the reverb tank, more current than that single triode can deliver, so two triodes are paralleled to provide adequate current drive.
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Thanks.
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Does anyone know if there's a way that DIY Layout Creator can "test" a layout that's been created for shorts or open circuits? I'm just trying to find a way to double check what I've created in my layout. I'm a little gun-shy because I've missed shorts in my previous layouts about 3 times, something I should have caught, and was hoping the software can assist.
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I'm asking now because I'm about ready to send my layout to Hoffman to create my turret board with turrets installed, and I want to make sure what I've done is correct. I guess if I discover an error in the board due to my mistake, I can just install myself some extra turrets where needed.
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Your eyes are the only proofreaders you have. I suggest to print the schematic and layout. Then use a highlighter to trace through small portions of the schematic and also trace through the corresponding portions of the layout. Resolve any differences you find. Rinse and repeat until you are confident that the layout agrees with the schematic.
Getting the layout to agree with the schematic is the most time consuming part of a project, especially with a complicated project such as you have. I suspect you'll even dream about layouts before you are done. :icon_biggrin:
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Sluckey-You're right about this being the most difficult part--at least I hope it is. And yes, I've been dreaming about layouts now for about 4 weeks. Not every night, but too frequent for my liking! Thanks. I'm glad its not just me.
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Just wait 'til you start troubleshooting in your dreams! :laugh:
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+1
:laugh:
I've been thanked a couple times by operators that called at 4AM n I "fixed something" in my sleep!! :sleepy2:
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I've done that before too. Its like you had an "epiphany"!
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I'm probably going to be ordering my custom turret board from Hoffman today or tomorrow with the turrets installed. I figure I'll purchase some extra turrets in case I need them. As to the turret boards, he sells 2 colors, but the black one he says is "non-conductive FR4-G10". What's the difference in the 2 boards?
Anything I should think of/plan for when ordering the board?
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IIRC there were some "black" boards floating in the either that were conductive, so I believe he's "making a distinction" :dontknow:
did you leave enough room to drill standoff holes?
I like to get those outta the way before I start adding wires n parts.
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Thanks. Yes, I"ve got about 1/2" clearance around the top and bottom edges that I can drill those holes where needed. Most of the turrets are 1/4" on center between them. Others have more spacing. I looked at Sluckey's builds and based on his comments and the information he's shown in the Vox build, it looks like he uses 1/4" on center spacing that works fine.
Question, when you install a resistor or a cap, do you run the leads down through the top of the turret, or do you wrap it around the body? I've seen it done both ways and didn't know if it matters, or if there's a reasoning behind one way or the other. Thanks.
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IIRC there were some "black" boards floating in the either that were conductive, so I believe he's "making a distinction" :dontknow:
Yes, I think Silvergun bought a black epoxy board that was made/designed to be conductive, but he didn't know it was made to be conductive.
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seen it done both ways
dealers choice;
what you want to "think" about, how many times will I un-solder, re-solder, and how will that effect the "other parts" at that turret.
so, cathode bypass caps get tweaked a lot, coupling caps same, power supply dropping R's. IF they're wrapped around turret, then you put a couple parts down the hole, it's harder to get to the wrapped parts.
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Well, I bit the bullet and after checking my layout 3 times and being "satisfied" I think its correct, I ran the DIY Layout Analyzer for a Hoffman Turret board, sent it up on Wednesday night to Hoffman to make, he mailed it out on Thursday (wow what service!) and I received it today. It really looks great--see image below. I've never seen a turret board before and I was really surprised at how small the turrets are. Really nice job. Now let's hope my layout works!
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fwiw;
typically I try n drill the boards standoffs prior to adding pieces parts.
do a few "dry run" layouts, considering what's "above" the board, how it fits with power supply wires, splitting the distance between tubes on one side and pots on the other (If you have tubes in back)
If you put in the same time building as designing, you will do well in the "ah, Sh :cussing: " phase :icon_biggrin:
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Do you drill the holes for off-board wiring as you come to a point where you need it, or try to do it before you start loading the board? Another question, I've seen one amp builder on YouTube who builds his boards in sections, and tests each section before going to the next. He starts out with the Power Supply, then the Pre-Amp etc. I was wondering if at least doing the PS first and testing it for the voltages that are needed at the caps would work and be a good idea? I guess the idea would be you can adjust the resistors more easily at this stage of the build to get the DCV that you need at the tube plates. Is there any issue with just running power from the mains, to the PT, then to the bridge rectifier, and then through the 5 caps/resistors that I have in my design? Thanks.
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I do test my PS "ahead of time", but I've been doing electronics ALONG time :laugh:
once I ohm check there is no short + to -, I calculate my PA tubes load, I calculate the value of a "DummyLoad" Resistor, INCLUDING watts. I gator clip the R for the PA tap, hook up a meter, power up n verify I'm in the ballpark.
as to "fly wire" holes, I drill them as I go, (probably NOT recommended). IF you don't have complete control on drill speed and pressure things can get ugly.
the key to this phase, slow, methodical, double checking after say 5 connections.
my "double-checking", after I do 5 connections, I walk away for 10 minutes, come back, trace out what I did, fix any "oops", If there are 3 oops in 5 connections, go do something else because you mind isn't where it needs to be. :w2:
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Do you drill the holes for off-board wiring as you come to a point where you need it, or try to do it before you start loading the board?
I drill wire pass-thru holes at the same time I drill turret holes. Same for standoff mounting holes. Much easier while there is nothing on the boards.
Since you have a board with turrets installed I suggest you drill any additional holes ***BEFORE*** mounting anything on the board.
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Thanks guys for the input. As to the PS testing, what I was thinking of doing is this: Nothing would be installed in the aluminum chassis at this stage. It would be setup on a wooden board, with a grounding lug screwed into the board to receive the grounds from the PT and the turret board. I connect the power cord to the transformer Primary, through a fuse, using wire nuts. I then solder the bridge Rectifier to the turret board, and solder the caps and resistors to their places on the turret board. I then connect the PT Secondary to the input on the bridge rectifier with wire nuts. I use my Variac to control voltage, and connect it to the light bulb safety board, and plug the power cord into the safety board. I would then connect a DMM to the ground lug and to the first B+ coming from the rectifier. Stand back and turn on the power at the Variac. Then hopefully read the voltage at that stage which should be the 410 DCV shown in the schematic. And then take the readings at B, C, D, and E. Does this work?
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which should be the 410 DCV shown in the schematic.
with no load, that voltage will be bigger.
before you turn on power, even with all the safety stuff, ohm across the PS rail + to red lead, PS - to black lead, you should NOT have anything < than thousands of ohms "charging" as your meters battery charges up the caps. IF you read like 27 ohms solid, STOP and fix.
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I'll definitely be taking this slow.
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I've identified where I should drill holes on the board to take the wiring under the board, and have a question about drilling the board. I have a small drill press that I'm going to use, and have a new 1/8" drill bit that I was going to use. Any tips on drilling the holes? Is the material that Doug Hoffman uses for the turret boards easy to work with or brittle? Any need to use a center punch first before beginning to drill? Any issues about staying a minimal distance from the edge of the board? Etc??? Thanks. Stephen
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Sluckey-what type of shielded cable is used for the volume pot, and for the input and reverb connections, and for the 470K 3W resistor as shown on the attached file? Also, which tubes would you use shielded sockets and covers for? Thanks. Stephen
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fwiw;
I like RG-174 for shielded cable
I shield ALL small signal tubes, including PI, (assuming 9 pin'rs)
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Do you use the RG-174 going from the ground to the 470K resistor too, or is that a different type of wire?
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ground to the 470K resistor too
quick glance, are you talking 470 to ground?
the couple 470k's I seen didn't go to ground, but I'm in a hurry :laugh:
If it's the 470, any wire works
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Yes its the 470K 3 watt resistor going to chassis ground. Its just that your VISIO layout showed it with a stripe or something, so I didn't know if it was special or just being pretty.
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I'm following this thread with urinary incontinence. Its like one of those movie where you really start rooting for the would-be hero guy. I can't wait to see how it plays out.
Dave
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Well said! I'm holding my legs together too!
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Sluckey-I'm using the Hammond 269JX PT, and just wanted to confirm the wiring as I plan this thing out. My mains are reading 122 VAC, so I'm going to use the 125V option and use the black and white wires on the primary to the input power, and tape off the gray. Then the 2 green wires will go through the power light and then on to the filaments. The 2 reds will connect to the 2 center terminals on the bridge rectifier, and the red/orange center tap will go to Chassis Ground. Is this correct? Thanks. Stephen
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The 2 reds will connect to the 2 center terminals on the bridge rectifier
DO NOT USE THAT TRANSFORMER WITH A BRIDGE RECTIFIER!!!
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What type of rectifier do you recommend I use? What I had purchased is a 3N259 bridge rectifier, 1000V 2 amp. That won't work?
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Sluckey-attached are datasheets for the transformer and for the rectifier if that's useful to you.
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500V CT, into FWB and capacitor, is 700V DC.
I'm tempted to let you try. But wear a face-shield.
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This will work. But it is poor economy.
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So should I just use 4 of the 1N4007G diodes in series as shown on the schematic? I thought that schematic was for a full wave bridge rectifier. Is what I should be looking at is a "full wave rectifier" vs. a "full wave bridge rectifer"? I was assuming that the part I had (the 3N259) did the same thing. Obviously not good to assume! By using the part I was going to use it seemed like it would be a neat easy fit.
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PRR--"poor economy" in what respect? Do you mean $ (the part was about $2.50--I also have the 1N4007G Diodes I can use if that's what's recommended) or an inefficient use of components that would denigrate the result? Thanks.
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PRR--"poor economy" in what respect? Do you mean $ (the part was about $2.50--
Yes. 1N4007s can be bought for $0.04 each, so it's a "poor ecomomic" choice. Your bridge will work fine as long as the negative terminal is not connected to anything. In fact, I suggest you cut the negative terminal/lead off flush with the plastic body just so it cannot ever be used.
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Sluckey-so if I wire it like PRR shows in the attached drawing, and cut off the negative lead as you suggest, what capacitor do I use to connect between the red/yellow center tap lead before it goes to ground, and the positive lead before it connects to the Node A power filter cap? The positive lead doesn't terminate at the cap does it? Thanks. Stephen
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Sluckey-so if I wire it like PRR shows in the attached drawing, and cut off the negative lead as you suggest, what capacitor do I use to connect between the red/yellow center tap lead before it goes to ground, and the positive lead before it connects to the Node A power filter cap? The positive lead doesn't terminate at the cap does it?
That IS the A node filter cap PRR is showing you in his drawing.
He is not showing you a 2nd A node filter cap.
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Thanks, I wanted to be sure.
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Sluckey-so if I wire it like PRR shows in the attached drawing, and cut off the negative lead as you suggest, what capacitor do I use to connect between the red/yellow center tap lead before it goes to ground, and the positive lead before it connects to the Node A power filter cap? The positive lead doesn't terminate at the cap does it? Thanks. Stephen
Look at the drawing again. The red/yel C/T wire connects directly to chassis ground. And the Node A cap positive lead connects to the positive terminal of your bridge. And the Node A cap negative lead connects to chassis ***AT THE SAME POINT THE RED/YEL C/T CONNECTS TO CHASSIS***.
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Got it. Thanks again.
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Meant to add this layout for the corrected rectifier wiring using the bridge rectifier with the negative lead removed--at least as I understand it.
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Ok, so I did a test of the rectifier today. I soldered the bridge rectifier to the turret board after having removed the Negative lead. I installed the Hammond 269JX transformer by screwing it down on a board. I grounded the mains green wire to one of the screws holding the transformer to the board, and then wired together the black and white wires on the transformer and the power cord. I grounded the Red/Yellow center tap wire to a different screw in the same board. Its just off by itself, with nothing else connected to it. Then I clipped the 2 red leads from the Secondary to the 2 AC connections on the rectifier. Finally I hooked up my DMM in DCV mode with the red lead to the + leg of the rectifier, and the black lead to the ground screw where the Center Tap wire is grounded. I didn't install anything else in the circuit, ie. no filter cap/resistors, etc. I ran all of this through a Variac and a light bulb limiter. Nothing blew up or smoked! My reading showed 239 VDC. I was expecting it to be around 350 VDC. So my question is whether my readings appear proper, and if not what's wrong. Thanks. Stephen
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I didn't install anything else in the circuit, ie. no filter cap/resistors, etc. I ran all of this through a Variac and a light bulb limiter. Nothing blew up or smoked! My reading showed 239 VDC. I was expecting it to be around 350 VDC. So my question is whether my readings appear proper, and if not what's wrong.
You have to hook up the 1st B+ filter cap, A node cap. Then take your reading. Without the filter cap, your reading will be way off. All your reading is the rectifier pulses, it will confuse your meter.
!!!!!!REMEMBER!!!!!! That cap will hold a dcv charge after you unplug the PT!!!!!! You have to drain it with a 220K or 330K or 470K resistor to ground, 1/2w will work or 1w or larger will be better. The R value is not a big deal, what ever you have that's close. The larger values will just take longer for the cap to drain off it's dcv charge. Leave the bleeder R hooked up for a couple minutes, larger R value, leave it a little longer. Then measure it for dcv to make sure all the dcv bled off.
I wouldn't hook the power cord green wire to the PT. Hook the power cord green wire, the PT B+ mains CT AND the filter cap negative lead together, 3 leads. You can strap the bleeder R across the filter cap when you do this, if so, then 4 leads grounded together. Or just use 2 alligator clip jumper cables to hook up the bleeder R across the filter cap to drain it.
!!!!!!BE CAREFUL!!!!!! Or it will bite you!
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Thanks this is helpful. I've got and used a "snuffer stick" before, but its good to be reminded, and keep one hand in your pocket. I was going to ask if I also need to install the resistor to the A Positive terminal, but I guess that's not necessary? And I can use the snuffer stick to bleed the charge from the A Node cap?
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fwiw
a big R like Willabe suggested can be clipped in when you clip in the cap, it's large R won't have much effect with power on, then when power is off, it's doing it's job - keeps those fun SNAP sounds at bay :laugh:
and ya, hum "one hand in my pocket, the other......." :icon_biggrin:
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So could I just go ahead and install now the A Node 2K 10W Voltage Dropping resistor at the B+ terminal of the A Node cap, and then ground the other end of the resistor to the chassis ground you describe for it to bleed off? Would that R be large enough?
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Don't connect that 2K/10W resistor to chassis ground!
If you want a bleeder resistor then permanently connect a 220K/3W directly across the Node A cap.
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Thanks Sluckey.
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Like the guys already said, NO!
At least 220K to 470K, 2K is way too low of a resistance.
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to pile one more :laugh:
try and keep Mr. ohm close at hand
to drain caps for safety, current can be real low, so low I = biggish vdc/real big R
if R is low, I goes up, and you want the I's in the amp to operate, not providing heat for the house :icon_biggrin:
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Success!!-I decided not to install a bleeder resistor and just used my snuffer stick to drain the cap. I checked the stick and it has 110K resistance and it only took a couple of minutes to get it down into the millivolt range. So it read 367 VDC! So that's consistent with the theory of the rectifier increasing the DCV to about 1.4 times the secondary voltage of 250. My question though is that the schematic shows a voltage of 410 VDC at Node A, and I'm at 367. Agree that I'm not going to be wiring Node A since I eliminated that part of the circuit, but is this an issue for the rest of the circuit. Node B shows 338 VDC, but when I install the 2K 10W voltage dropping resistor between Node A and B it will lower the 367 VDC--but to what value? I know this is a holiday so I realize you all probably have more interesting things to do. Thanks again. Stephen
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IIRC all the tubes are small bottle NOT PA
so there is no problem with voltage, probably won't drop much under load since each triode only draws a few mA's
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Sorry, but can you translate this phrase for me "IIRC all the tubes are small bottle NOT PA"? Thanks.
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IIRC = if I recall
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I thought that was some technical electronic tech speak!!!! Yes, no Power Tubes, all 9 pins.
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IIRC = if I recall
And/or; if I recall correctly.
PA= power amp. (Here referring to the power amps tubes).
Snuffer sticks 110K is fine for draining the cap. Too small to leave in the B+ power supply.
2K would drop too much dcv across itself and might burn up along with the PT, over working the PT. Unless you went with a very large wattage 2K R, but that would just save the R, not the PT. More wattage=more $$, but no need. And if you left it in, it would drop the B+ dcv, a LOT of waste.
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So I guess what was confusing me was the type of rectifier in the circuit schematic. I saw 4 diodes so I thought it was a full wave rectifier, not realizing the difference between that and a full wave bridge rectifier. So I learned about the use of a PT center tap with the full wave rectifier but not with the bridge rectifier. Also, can I ask, why does this circuit use 4 diodes for the rectification rather than just 2, which seems to be the way they are usually designed--at least based on some of the Youtube videos I've seen? Thanks.
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PIV :icon_biggrin:
typically when you see 4 it's because of large "spike" potential that could cause a diode to fail.
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So does it make sense for me to install the remaining filter caps and voltage dropping resistors now to be sure each node meets the output voltage values called for in the schematic before doing anything else on the build?
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No, there's no current draw, so the B+ dropping R's wont drop any dcv.
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Also, can I ask, why does this circuit use 4 diodes for the rectification rather than just 2, which seems to be the way they are usually designed--at least based on some of the Youtube videos I've seen?
Like shooter said, PIV = peak inverse voltage. Look it up and read up on it.
From Merlin's web page;
http://www.valvewizard.co.uk/bridge.html
http://www.valvewizard.co.uk/smoothing.html
http://www.valvewizard.co.uk/psu.html
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Thanks for the lead on the articles. I'll check them out today.
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Sluckey-I woke up at 4:30 this morning thinking about this. Since I've taken the Power Amp out of the circuit, is there any need for the 100K Volume Pot at the output? Is the signal supposed to be at the same level going out as it is at the input? Also, what is the purpose of the Volume Pot after the pre-amp stage? Thanks. Stephen
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Sluckey-I woke up at 4:30 this morning thinking about this. Since I've taken the Power Amp out of the circuit, is there any need for the 100K Volume Pot at the output? Is the signal supposed to be at the same level going out as it is at the input?
The signal level at the output of V7 is BIG, big enough to drive a power amp. But since you will be connecting this unit to the instrument input of another amp, you need a way to knock that BIG signal back down to instrument level. So, I added a 1M plus the 100K pot to make a 10:1 voltage divider just to knock that BIG signal down. The 100K pot allows fine adjustment of the output level.
Also, what is the purpose of the Volume Pot after the pre-amp stage? Thanks. Stephen
It's the volume pot from the original M10A. Turns the volume up and down.
IMO, both pots are desirable and even necessary. In fact, I had considered putting a switch across the 1M resistor that feeds the output level pot. This would provide a "line level" output as well as an "instrument level" output. This would allow you to also plug this unit directly into a power amp if desired. If I were to build this I would put the switch in.
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Yes, I woke up wondering about the size of the signal at V7. I assumed the level would need to be reduced, but I was concerned that with the pot, a user could overdrive the output signal. So I assume the 1M resistor reduces the level so that won't happen. I was thinking you might just recommend a resistor rather than a pot. But I understand the flexibility the pot gives. I intend to run a guitar through this device and then out and through the Fender Champ I built, but it could be used with other amps too. What type of setup are you thinking of for using it with just a power amp? As to the switch, would it just be a SPST? Thanks.
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I'm starting cutting out the holes for the chassis, and need to decide about the foot pedal(s) for the vibrato and reverb. I'm mounting the vibrato/reverb jack(s) on the bottom of the chassis where the tubes will be, along with the RCA jacks for the reverb tank. I would like to use 1 jack controlled by a single foot pedal that has 2 switches--like the Fenders. I assume it terminates in a 1/4" stereo jack. But are there issues to consider that would go in favor of 2 separate foot pedals? If just one jack is used, would it be a stereo 1/4" jack or something different? Thoughts?
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Sluckey/Shooter/et al: Do any of you see any issues with the tube/reverb tank jacks/or reverb-vibrato foot switch jack placement shown in my attached layout?
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Your layout is fine. No problems using a 1/4" stereo jack. The cable must be shielded for the reverb but vibrato wire does not need to be shielded. I suggest using a Fender reissue footswitch...
https://www.tubesandmore.com/products/footswitch-box-fender-two-button-vibrato-reverb-vintage
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Thanks Sluckey. I really appreciate your help with this project. Stephen
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Does the wiring into the RCA Input/Output Jacks for the Reverb Tank connections also need to be shielded?
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The cable must be shielded for the reverb
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Does the wiring into the RCA Input/Output Jacks for the Reverb Tank connections also need to be shielded?
Not needed if the wires are only a couple inches long. Otherwise use shielded cable. Same for wires between reverb pot and circuitry.
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Thanks. The folks at Antique Electronic Supply got me the info on the wiring of the plug for the foot pedal: The tip is the vibrato and the ring is the reverb. I"m finishing up drilling the holes for the chassis today or tomorrow, and then will start the chassis wiring.
Two questions on wiring the filaments. First, do I need to install a 100 ohm resistor (for a total of 2 resistors) on each filament lead from the transformer secondary to the Fender style pilot lamp I'm using? My Hammond 269 JX transformer doesn't have a center tap for the filament leads, just for the main leads. Second, do I use pin 9 on these tubes, or just run both the leads to filament pins 4 and 5?
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Also, can I ask, why does this circuit use 4 diodes for the rectification rather than just 2, which seems to be the way they are usually designed--at least based on some of the Youtube videos I've seen?
Like shooter said, PIV = peak inverse voltage. Look it up and read up on it.
From Merlin's web page;
http://www.valvewizard.co.uk/bridge.html (http://www.valvewizard.co.uk/bridge.html)
http://www.valvewizard.co.uk/smoothing.html (http://www.valvewizard.co.uk/smoothing.html)
http://www.valvewizard.co.uk/psu.html (http://www.valvewizard.co.uk/psu.html)
Did you read this and search out PIV?
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Two questions on wiring the filaments. First, do I need to install a 100 ohm resistor (for a total of 2 resistors) on each filament lead from the transformer secondary to the Fender style pilot lamp I'm using? My Hammond 269 JX transformer doesn't have a center tap for the filament leads, just for the main leads.
The resistors are necessary to reduce hum. Each resistor connects from a filament lead to chassis. Fender was fond of physically connecting them between the pilot lamp and chassis but you can place them anywhere that's convenient.
Second, do I use pin 9 on these tubes, or just run both the leads to filament pins 4 and 5?
Do it the same as you did in your champ. For all these tubes... connect one filament lead to pin 9. Connect the other filament lead to pins 4 and 5 (jumpered together)
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Gotcha-So they're wired in parallel keeping it at 6.3 V, rather than running them in series from the 12.6 V pin 9.
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Gotcha-So they're wired in parallel keeping it at 6.3 V, rather than running them in series from the 12.6 V pin 9.
That's backwards.
You use pins 4 and 5 to run them in series.
Pin 9 is the center tap point between the 2 filament heaters.
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Slukey-I was thinking of installing a grounding lug to the chassis in an open area between tubes V6 and V7, and move the 2.7K and 270 ohm cathode resistors from the ground bus wire running along the top edge of the board and connecting those resistors directly to those tubes and then ground them to chassis on the added lug. In fact I could also do it with the 2.7K cathode resistor on V1. Thoughts? Is this likely to create a ground loop problem? I"ve attached a current version of the layout for you. Thanks.
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Is this likely to create a ground loop problem?
Link for grounding;
http://www.valvewizard.co.uk/Grounding.html
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I would just copy the ground scheme on the original. :l2:
http://sluckeyamps.com/magnatone/M10A_guts.jpg
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Wow, what a mess!
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Running the wire for reverb- and tremolo footswitch inside the same shielding may induce tremolo into the reverb-recovery.
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Running the wire for reverb- and tremolo footswitch inside the same shielding may induce tremolo into the reverb-recovery.
Not a problem for the Fender footswitch cable.
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Do I need to use this type of cabling to connect the vibrato and reverb circuits to the stereo output jack, or just regular hookup wire?
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Do I need to use this type of cabling to connect the vibrato and reverb circuits to the stereo output jack, or just regular hookup wire?
No. This cable is only used for the footswitch. Use regular hookup wire inside the chassis for the Vibrato. If reverb wire is more than a couple inches long use regular shielded cable.
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Sluckey--I"m starting to install the hardware in the chassis. Do the input or output jacks need to be insulated from the chassis? Is the shielded input jack wiring grounded at the main ground near the jack, but not grounded at the other end? Finally, for now, is the connection of the shielded input wiring that connects to a resistor and a cap, that then connects to the grid on V1, as shown in the attached layout image, attached to a lug that is insulated from the chassis? Thanks
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As to the two 100 ohm resistors needed for the filament leads, I only have 1/4 watt 100 ohm resistors (unless I order 1/2 watt), but I do have 270 ohm 1/2 watt resistors. Will either of these work okay, or should I just go ahead and order the 1/2 watt 100 ohm resistors? I don't have a store within 70 miles of where I'm located, so its a real pain to get anything unless ordered online.
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Do the input or output jacks need to be insulated from the chassis? no
Is the shielded input jack wiring grounded at the main ground near the jack, but not grounded at the other end? yes
Finally, for now, is the connection of the shielded input wiring that connects to a resistor and a cap, that then connects to the grid on V1, as shown in the attached layout image, attached to a lug that is insulated from the chassis? The wire and resistor connect to an insulated standoff turret, but the cap connects to a ground lug that is secured to chassis with the same screw that secures the standoff turret. You may wish to use a more common terminal lug.
As to the two 100 ohm resistors needed for the filament leads, I only have 1/4 watt 100 ohm resistors Each resistor only dissipates 0.1W so 1/4W resistors will be fine.
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Thanks.
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Should the RCA jacks going to the Reverb Tank be insulated from the chassis? I have the Switchcraft 3501FR RCA jacks, like is shown in the image below. I also got some fiber washers with shoulders that I could put between the rim on the jack and the ground lug that follows, and then the nut. Is this overkill?
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Should the RCA jacks going to the Reverb Tank be insulated from the chassis?
no
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Well I've pretty much completed the infrastructure and did the filament wiring, as you can see. Pretty tedious, but very satisfied. I'll work on some more of the off turret board wiring tomorrow.
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Not to cause you to do extra work or anything, but I see two things about your filament wiring that I would change.
1. Looking at the picture, it looks like your filament leads from the transformer come inside the chassis and then head straight north, go under some of the control pots and then go west toward the lamp. I would reroute those and have them go west straight out of the hole and keep them away from those control pots. Might be fine as-is, but filament wires are one of the places where noise can come from, so keeping them away from those pots would be an anti-noise precaution.
2. You can run the filaments as you did, twisting them and running them along the chassis (many commercial amps were done this way), but I think you'll find that the common (again noise reducing) scheme is to raise them above the tube sockets. Look up ab763 gutshots on yahoo or something and look at the pictures. You'll see what I am talking about. I went ahead and attached a picture. I would do it neater and tighter than the picture, but you get the idea.
Dave
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Thanks Dave for your insight and suggestions--The filament leads from the PT go under the Vibrato Speed and Intensity Pots. I was concerned that having them go under the turret board would expose components to possible noise, but as I look at the layout, the wiring as you suggest would be going under the reservoir and filter caps. So I'm guessing its not an issue. Unless someone has another perspective on this, I'll rewire as you suggest. As to the filament wiring on the tube sockets, I'm going to let that stay as is. It was pretty tedious, plus I'm out of filament wire! I appreciate everyone's input to my project. Stephen
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You are very welcome. I think you'll note that there are a lot of folks rooting for you because not only do we want you to succeed in this build, but many of us are excited to see how it turns out because (at least in my case) a future project may be germinating in the recesses of my mind.
Dave
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Sluckey-Do I use shielded RG-174 cable to connect the #2 lug on the Main Volume Pot to Grid pin 7 on V1 tube socket, and leave the ground in the shield disconnected at both ends? Also use the same type of cable for the input jack to Grid Pin 2 on V1?
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Connect the shield to the ground lug of the volume pot. Use the same type cable for the input jack.
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Sluckey-I"m starting to work on installing components to the board, and wanted your thoughts on where/how to ground the 4 filter caps as shown in my layout attached. I assume they shouldn't be grounded to the ground bus that I'm connecting the pots and pre-amp, etc. to, but should use a different location. Thoughts? Thanks.
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I don't think it really matters since this whole unit is a preamp.
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Thanks.
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Well I started loading the board today, and made pretty good progress. Its pretty tedious, but that's part of what its all about. I got through the pre-amp and the first pair of varistors installed, and called it a day. I'm pleased with it. Not as pretty as Sluckey's or Shooter's, but just hope it works. Now its time for a bourbon!
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You should see some of my builds. Sluckey would probably slap me if he saw how I go about building an amp. My method is as follows, come up with an idea. Very little prior planning except an idea of how big the board needs to be based on what a old Fender might look like with similar features. A power transformer that will provide what I need for the basic plan. Start building it so that it looks similar to what a typical fender layout might look like. Try to leave a little room here and there on the circuit board in case I need to make revisions or I want to add something later on. Build it. Go back and redo the stuff that wouldn't fit.
As long as my amps look better than a Silver Face Fender I'm pretty happy. I usually shoot for Black Face, but my amps tend to be a little more busy, so I settle for a pretty Silver Face. Hey, but all my amps have worked well. Except the one I'm currently working on. More to come on that.
Dave
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Now its time for a bourbon!
:icon_biggrin:
I'll smoke to that!
want tedious AND pretty;
one the "frayed" end, put an inch or so of shrink tube, after you pushed back to expose wire, then heat to hold. (practice while sippin :)
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Beer nuts for thought;
Don't rush this part
your solder looks solid on the cap, my recommendation, top of yellow cap, wrap the lead around the jumper, I like 3 wraps, but have been known to just do 1 :angel
the bottom, good flow, kinda cool imagery, again I would leave the R on left "up some" then wrap the cap.
the reason, solder is a poor conductor so we want a good mechanical bond.
put on the tunes, sip while "thinking", once you "unlock" the turret n friends, work it like origami, or bonze, save bull dozer driver for yard flatting :laugh:
edit attachment :think1:
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Thanks everyone--your comments are really helpful, and I'll try to incorporate them when I pick up tomorrow. I may go back and make some adjustments. Here's the question: Is there some way that I can test the circuit at its various stages to make sure things are doing what they should be? I know I can check for grounding, but I'd hate to get to the end of this and find a problem--if there was some way I could have done testing at each phase of the circuit. Thanks again for your interest and support. Stephen
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I think it would be pretty hard to do that unless you have the entirety of the amp connected and running. If that is the case, you can search Doug's library for the "listening amp" which is a little amp that will let you tap into your amp at different places to see if it is function up to that point.
Before you have voltages applied, I don't know how you could do it if at all.
Dave
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Here's the question: Is there some way that I can test the circuit at its various stages to make sure things are doing what they should be?
I usually make some power on checks of the power supply before early on. But as for the rest of the amp, it's best to just get it wired up, then compare your schematic, layout, and actual wiring to be sure they are all in agreement. This is why it's so important to spend so much time on the layout drawing. Finally, just plug it in, check voltages, and hope it works. If not, it's time to improve your troubleshooting skills.
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Well as the old song of The Temptations goes "Its Growing"! See attached photo. Seems to be moving along smoothly. I think the best advice I've gotten from you guys on this project, so far, was to take the time to create a Layout--don't wing it! It did take a lot of time to do the layout, and hopefully I read the schematic correctly-with your assistance in some instances, but I find that not only does the layout speed up the installation of the components, but if I had not created it, the installation by just reading from the schematic would have been filled with problems and errors. So I'll keep you posted.
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Sluckey--Catastrophe (maybe) averted!! I was installing the last resistor in the circuit, a 270K that connects to the plate on the V4 tube, and I couldn't find the resistor among the packets that I got from Mouser. I checked the circuit and saw that there are 2 other instances of the 270K that connect to the 2 plates in the V7 tube, and also just a small 270 ohm (not a 270K) that connects to the V6 cathode pin. I kept looking through the packets and saw a packet of 270 ohm resistors, and also a packet of 2.7K resistors, but not 270K? So I thought, maybe I screwed up the order and the installation. Sure enough, the 2 resistors on the V7 were in fact 270 ohm resistors and not 270K ohms. I didn't order 270k's, but ordered more 270's than I needed. Lucky for me SLuckey! So I disconnected them, and ordered the correct resistors from Mouser! Just out of morbid curiosity what would have happened if I had not caught my error? Thanks. Stephen
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It wouldn't have fried anything. Just wouldn't have worked and you've been digging around trying to figure out why you had such high voltages on the plates of that tube and no signal.
Dave
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Dave-whew! That's good to know.
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Sluckey-while I'm waiting for the correct resistors to arrive, I thought I would wire the jacks for the Reverb input and output. In looking at the schematic attached below, am I correct that both of the jacks are grounded? The way I'm reading the schematic, the negative end of the 1uf cap coming off of Plates 1 and 6 that are jumpered, lead to the "tip" connection on the input jack going to the tank and the shield lead connects to ground. And then the "tip" lead on the reverb return jack connects to the Grid 2 pin on V7, with its shield also connected to ground. Am I correct? If both jacks are grounded, then won't both of the jacks on the Reverb Tank also need to be grounded? The folks at MOD said that the 4FB3A1B tank that I was planning on getting say that the tank has jumpers at the jacks that can be unsoldered and changed to both grounding--That's what I understand I would need to do for this tank, assuming I'm correct in the wiring. Thoughts?
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Both reverb jacks on the original M10A are grounded to the chassis. I have no idea about the jacks on the original reverb tank. I suggest you plug into your tank and try it without messing with any ground jumpers. If you have a hum that cannot be resolved inside the chassis, then play with the jumpers.
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Thanks.
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Both reverb jacks on the original M10A are grounded to the chassis.
Let me back up and retract that statement. There are no reverb jacks on the chassis. The reverb cables are hard wired on the chassis with rca plugs on the end that connect to the reverb tank. My pics are not detailed enough to see if the shielding is connected to the chassis but I really suspect that's the case. Not gonna open the amp to verify. Sorry.
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Is there any reason not to install RCA jacks on the chassis, and wire from the circuit board to them? Then I would just plug the RCA cables into those jacks and the jacks on the reverb tank.
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I've got a fitment problem. The 2K 10W wire coated cement resistor connecting between 40uf Cap 1 and 40uf Cap 2 is way too big physically to fit! Remember I won't be using Cap 1 in the circuit because it would have been feeding a part of the circuit that's been eliminated. So is there a substitute I can use to connect those 2 caps?
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The 2K 10W wire coated cement resistor connecting between 40uf Cap 1 and 40uf Cap 2 is way too big physically to fit!
That happens when you don't use properly scaled components on the layout. Looks like you used a 1/2w resistor on the layout.
Maybe the 10 watt resistor is way oversized. You could try a 2K/3W and when it's up and running measure the voltage across the resistor and calculate the actual power being dissipated. Double that number for a safety margin. If it comes in under 3 watts then you're fine. Otherwise you'll have to figure out a way to mount the 10 watt resistor.
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fwiw;
sorry for poor detail;
this is how I "shoe-horned" in a 10w'r in a 5w space
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Fair point Sluckey. Is the 10 W resistor going to be dissipating a lot of heat so that it shouldn't touch other components? Shooter, thanks for the image. I might be able to get that to work. I just am concerned about the heat issue--is it an issue?
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Does the fact this circuit has been redesigned to become, as Sluckey said, just a pre-amp and not an amp powering speakers, impact this? Could I connect 2 resistors in parallel with each being 2K ohms, but being 2 or 3 watts resulting in 4 or 6 ohms by wiring in parallel, be an option?
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Fair point Sluckey. Is the 10 W resistor going to be dissipating a lot of heat so that it shouldn't touch other components?
Yes. Heat is an issue, otherwise Magnatone would have used a smaller/cheaper resistor. All power resistors should be given enough air space to dissipate heat.
Shooter's method is a good one.
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Does the fact this circuit has been redesigned to become, as Sluckey said, just a pre-amp and not an amp powering speakers, impact this?
In this case, not enough to really matter.
Could I connect 2 resistors in parallel with each being 2K ohms, but being 2 or 3 watts resulting in 4 or 6 ohms by wiring in parallel, be an option?
You would need two 4K in parallel to equal 2K.
I would mount the resistor as shooter suggested.
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I think I solved it. I moved the #2 40uf cap to where #3 30uf cap is, and put #3 in the #2 position. This also gave me more space with the pilot light housing. Then I mount the 2K/10W resistor at positions #1 and #3. And by mounting it up rather than at the base of the caps, I get a lot more air circulation. Then I switched the wiring from the + sides of those 2 caps, and switched the position of the 2 resistors. #4 Cap stayed where it always was. I haven't soldered anything, but take a look at the photo. Issues?
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:thumbsup:
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Sluckey, I'm finalizing how to ground the footswitch, and the input/output reverb jacks, and the cathode pin 8 on V4, and would appreciate your thoughts. The input/output jacks are grounded to the chassis through their shields as a result of screwing them onto the chassis. Those jacks also have their shields jumpered. Should I run a jumper from pin 8 to the shield tab on one of those jacks and use it as the ground, or should I install a small terminal strip which is screwed to the chassis and run all of the wires to that? If so, should I use the terminal strip's connection to the chassis as the ground connection, or run a wire from the strip to the ground bus where everything else attaches? Thanks.
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I would ground V4-8 to the same place that V4-3 cathode resistor is grounded.
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Thanks.
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I'm at the stage where the board is finished and I'm about to install it in the chassis and wire up the tube sockets. Does anyone have any thoughts on how to test the work I've done on the board so far? It will be a real pain if I have to remove the board after wiring it up to the tube sockets (they're surface mounted because of the tube covers) in order to remove and work on the board. Thanks.
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About all you can do is verify your schematic, layout, and actual board all agree. Correct components, correct jumpers. Verify that any underboard jumpers are securely soldered such there is no chance of one coming loose when you solder on top of the board.
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Thanks. Well its good to know that I've done all of those things, so hopefully I haven't missed something and things will go smoothly.
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Don't worry do much. Chances are high that you screwed something up. It happens regularly. Half the fun of building stuff like this is figuring out what's wrong when it doesn't work. By half the fun, what I really mean is super frustrating and annoying learning moments. Where you make a discovery that translates to one mistake you will never make again. Once you have made 100 mistakes that you will never make again, you will be a guru.
Dave
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Most likely true!!
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Sluckey-I wired the input cable from the input jack as shown in the attached layout that you did for me, with the lead of the shielded cable connecting to the switch lug (not the tip lug), and with the shield connected to a separate ground at the chassis. The switch lug and the ground lug are jumpered, and will go to the ground buss bar, but of course the ground lug is also grounded via the chassis because of the jack's attachment to the chassis. Should the "lead" be connected to the switch as you show in your layout? I thought maybe it should be connected to the tip at the input jack. The reason is that when I ohm out the lead at the other end where it will connect to the V1 tube, it shows continuity--so its grounded. That doesn't seem right. It's connection to the 47K R is supposed to be isolated from ground. Thoughts?
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Should the "lead" be connected to the switch as you show in your layout?
No. That's a layout error. Connect the lead to the tip as shown in the schematic you attached.
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Thanks. I was thinking maybe the shield was touching its lead somewhere-like maybe the insulation on the lead had melted, etc.
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Well the wiring is complete except for running the main ground buss and attaching the grounds from the pots!! Looks really good. Let's hope it works really well too. I've got the tubes and reverb tank ordered, so it probably won't be in until later next week, so I've got time to go back over the circuit and check everything and the connections. When someone gets a chance, I would appreciate your thoughts on starting it up and what readings to check, etc. Thanks. Stephen
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I've got all the wiring to the buss finished, and so I'm just waiting for the tubes and reverb tank. I've checked the wiring and the circuit seems fine. Here's what I did. I set my DMM to the continuity setting where it beeps when there's continuity. Then I went to each tube socket on the side where the tube would be inserted, and put 1 probe in one pin and the other probe in the adjoining pin, and went around the circle from one pin to the next. No beeps. Pins 4&5 did beep but they're jumpered, and they also beeped when each was connected with Pin 9. I also confirmed each connection to the buss beeped where it was supposed to, and checked the other components with 1 probe grounded to chassis, and none of them beeped unless they had a ground connection off the buss. All of the grounds for the jacks beeped. Any flaws with my methodology, or anything else I should check out? Thanks for everyone's help on this project.
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I set my DMM
besides what you've done;
I also like to set it to resistance NOT continuity, then put one lead in the tube socket
plate pin,(tube side), the other on it's corresponding "B+" tap, verify the R value. repeat for cathode socket pin to ground. repeat
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Thanks. I just tried that and they checked out fine too.
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Still waiting for the tubes and tank. I'd really like to plug it in and test it. Should I ? What can I check out?
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Sluckey, Shooter, et al, my tubes and reverb tank came in yesterday, so I guess I'm ready to light this candle up tomorrow. Any tips, procedures, plate voltage readings or otherwise that I should follow? Should I turn it on initially without the tubes installed? Thanks to everyone for your help on this project.
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Should I turn it on initially without
fwiw;
I typically do, I measure all my volts at the tube side socket, that way I "catch" mis-wires, (B+ on filament kinda thing) the volts will be high-ish
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Well, I guess I should let you know how it went. I got it setup with no tubes and turned it on and nothing blew up. So I decided to go ahead and added the tubes and plugged in the Champ and my Strat and turned everything on. The tubes lit up but not very brightly. And I gave it a minute to warm up. AND IT WORKS!!!!!! The Vibrato and the Reverb sound great!! I just can't believe it. I just can't believe it!!! I'll send you some meter readings and a video or sound clip later. Just want to thank all of you again for your help and support!! WOOOOOOOOOOOO
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Congrats! You certainly put in a lot of time and effort and planning into this project. And it shows. Gotta feel very rewarding. Enjoy
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Hooray, congratulations!!!!!
Dave
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Thanks everyone. I've been running it some today to see if things need to "settle in". I'm running this through my 5F1 Champ kit that I built a year or so ago. I'm going to share some meter readings in a moment, but here are my initial reactions: There is no hum coming from the unit. When the output volume is turned all the way up you can barely hear the vibrato oscillation in the background, assuming it is switched on from the foot switch--but very minor and only if you aren't playing. The reverb has great range and plenty of volume/intensity. The vibrato effect is really unique. The Intensity of the vibrato could be stronger. The Vibrato speed is very noticeable when adjusting it, and has a really good range of speed. I've poked around the tube pins and hear crackling on 1 or 2 of the plates at tubes V5 and V4. I think its probably a bad solder joint. You only hear it when you poke around.
So I did some plate voltage measurements and they all seem low vs. what the schematic shows. I connected the red lead of my DMM set to DCV to the plates and the black lead to chassis.
Readings taken at each plate are as follows:
V1-Pin1-E Node-212v schematic Actual: 122.0
Pin6-D Node-256v 128.7
V5-P1-C Node--316v 188.3
P6-C Node--316v 195.6
V6-P1&P6 jumped-B Node-338v 174.6
V7-P1-E Node-212v 100.5
P6-C Node-316v 143.4
V4-P1 B Node-338v 190.9
P6 B Node-338v Fluctuating-maybe lose solder
It seems like these actual readings are each about 1/2 of what they show on the schematic. Is that correct?
The readings at each node of the caps with no tubes installed/tubes installed:
A--410 schematic Actual 357.0/320.1--Note that A node is not being used because circuit eliminated
B--338 350.0/263.6
C--316 347.8/249.9
D--256 332.9/224.1
E--212 318.4/202.8
For the filaments, I've got pins 4&5 jumpered, and then pin 9. Pins 4&5 are daisy chained and Pins 9 are daisy chained together. Pins 4 read 3.3 VAC, Pins 5 read 0.1 VAC, and Pins 9 read 3.3 VAC for all of the tubes. Is this ok?
So any comments you have about these readings would be appreciated.
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Pins 4 read 3.3 VAC, Pins 5 read 0.1 VAC, and Pins 9 read 3.3 VAC for all of the tubes. Is this ok?
not clear here;
4 & 5 are typically shorted together and get one filament wire, pin 9 get's the other
I typically measure cathode vdc, use the cathode R to calc I, ballpark ~~~ 1-5mA idle
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I fully expected to have to fine tune the B+ rail. Change that 2K/10W to 100Ω/1W. Remeasure and post voltages for B+ nodes A through E and let's see where you are.
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Sluckey, thanks. Yes pins 4 & 5 were twisted to face each other and then 1 filament wire ran through them and on to the next socket, and the other filament wire came off of 9.
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If you don't have a 100Ω or other low value resistor, just replace the 2K/10W with a jumper wire and recheck voltages.
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re-check fil also, they're probably good, but you're indicating 3.2v across a short
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As to the filament wiring, this transformer doesn't have a center tap for the filaments, so I put a 100 ohm resistor on each of the filament wires from the transformer at the pilot light, twisted the other ends of the 2 resistors together, and then grounded that connection on the ground buss. Then ran the filament wires first to V4, since it was closest, and on down the line and ended up with V1. Does this sound correct?
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The only way to accurately measure filament voltage is to put one probe on one pin of the socket and put the other probe on the other pin of the socket. Ex., for a 12AX7 tube wired for 6.3vac operation, put one probe on pins 4/5 and place the other probe on pin 9.
Did you increase the B+ yet? And?
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Thanks. I'm just getting started in a few minutes. I'll let you know what I read. I realize now that when I read the filament voltages yesterday, I had the black probe grounded to chassis, and only read the filament with the red probe. My mistake. So hope that checks out ok. If so, then I'll remove the 2W resistor and replace with a jumper between Caps A & B.
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If so, then I'll remove the 2W resistor and replace with a jumper between Caps A & B.
You don't have to actually remove that 2K/10W resistor. Just temporarily solder a jumper across it's easily accessible leads. The real fix is to replace that resistor with a much smaller value, something around 100Ω and 2 watts. Having a resistor between caps A and B will provide better filtering than a wire jumper.
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I just checked the filaments, and they're all reading 6.5 VAC. So to be sure I'm measuring cathode voltage correctly, do I set the DMM to DCV, connect black lead to chassis, and then probe each cathode pin with red lead?
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Why are you wasting time checking filaments and cathodes??? You already said "AND IT WORKS!!!!!! The Vibrato and the Reverb sound great!!".
Your next task is to try to get the B+ voltages to look more like the original. When you do that, then it's time to measure cathodes and record them on a schematic for future reference.
Any cathode voltages you measure now are subject to change when you increase the B+.
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Gotcha.
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Ok, here are the cap readings: actual vs. schematic
A--328/410
B--327.9/338
C--310.7/316
D--278.8/256
E--252.2/212
Pretty close except for E. Thoughts?
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How does it sound now? Is the vibrato stronger?
I'm not concerned about node E but it you want it to be closer to 212, then change the 10K resistor between D and E to a 22K 1W.
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Yes, the Vibrato sounds much stronger than before. You don't really hear it though until the Vib Intensity pot gets up to around 2 o'clock position, with a max out at 5 o'clock where the pot stops. I do notice that when the Reverb is active you hear oscillation of something even if the vibrato is not active. If you turn off the Reverb then the oscillation goes away even if the vibrato is turned on. If you turn the vibrato intensity to the max then the oscillation stops.
I did check the cathode VDC and their readings are as follows:
V1--1.034/1.490
V5--158.7/210.5 ****
V6--5.96
V7--1.234/1.950
V4--83.0/0.1 ****
So V5 and V4 really seem strange given the other readings. Thoughts
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Compare these voltages from my M10A. You must disable the oscillator for voltage checks on V4 and V5 (see the notes below the voltage chart on page 3.
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Looks like my voltages are pretty similar to yours. Any thoughts on the oscillating sound only when the reverb is active. Its much more noticeable after jumpering the 2W R at Node A-B? Does the range on the Vibrato Intensity pot seem typical, or should it the vibrato be more noticeable earlier in the pot range?
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Any thoughts on the oscillating sound only when the reverb is active. Its much more noticeable after jumpering the 2W R at Node A-B?
No idea about the reverb. Could be related to layout, grounding, wire dressing, wrong value component, etc. It's more noticeable because you have higher voltages now. There ain't no 2W R between nodes A-B. It's a 2000Ω 10 Watt. The jumper was meant to be a quick test. Now replace that big resistor with a 100Ω 2 watt.
Does the range on the Vibrato Intensity pot seem typical, or should it the vibrato be more noticeable earlier in the pot range?
I bet you used an audio taper pot? Replace with a 1M-L (linear) pot and see if that spreads the intensity control a bit more evenly. BTW, you may notice that I didn't specify any pot taper on my schematic. That's because Magnatone didn't either.
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Thanks Sluckey. I don't have the resistor, so I'll have to order it from Mouser probably (no electronics parts suppliers within 75 miles of Charlottesville where I am). Yes, the oscillation really wasn't as noticeable before by-passing the resistor. Yes all of the pots are audio taper (Log). I'll get a Linear taper and see how that works. What is the other type, a Reverse Linear/Audio, or something like that. I've seen that used in some tremolo circuits. Would that be appropriate for this design? Should I leave the jumper in place and play it while I wait for the parts, or is it better to take it out now. Thanks again.
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Should I leave the jumper in place and play it while I wait for the parts
Yes. What were the V4 and V5 voltages when you disabled the oscillator?
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I haven't disabled the oscillator yet, and was going to ask you how to do that.
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see Reply #356
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Sorry, I missed that.
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So I jumpered the resistor by manually (not soldered) attaching a jumper wire to each side of the resistor, and then read the DCV at the cathodes and plates for V4 and V5.
V4-Cathodes Plates
P3-83.0 240.4
P8-0.1 Fluctuating-190-240
V5-Cathodes Plates
P3--158.7 236.3
P8--210.5 243.8
Thoughts?
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Fluctuating plate voltage means you did not disable the oscillator.
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How would you disable it other than jumpering the leads on the R and soldering the jumper to the leads?
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I would use a gator clip test lead connected across the resistor leads. Or you could do it exactly as you jumpered the 2000Ω resistor. Once you do that the oscillator stops and the voltages will become steady.
Hard to say about V5. You need to post voltages for pins 1, 2, and 3 and also 6, 7, and 8. May be some clues there. Your voltages don't necessarily mean anything is wrong but the difference between yours and mine make me want to investigate.
Show me a hi-rez pic of V5 and the area of the board with the V5 components.
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Here are the DCV readings from V5, and the photo attached:
P1--236.8
P2--156.8
P3--160.6
P6---244.4
P7--121.7
P8--211.1
Thanks.
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There are several differences in my preamp circuit and yours and that probably accounts for our V5 voltage differences. Since you like the vibrato I'm not concerned about your V5 voltages.
We're at a point that I will probably be asking you several times to change resistor values. If you're gonna have to order a resistor everytime I ask, this is gonna get expensive and will drag on long past my attention span.
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Sluckey- sure, I understand the "attention span" issue. You've certainly devoted a lot of your time to my project, and I appreciate that. It may be that I have left over resistors to try, but I'll deal with that if I need to. I guess my question is would your suggestion for my testing going forward be for the purpose of eliminating the oscillation sound when the reverb is on, or something else? I'll try disconnecting the oscillator this morning to see if I can get some steady readings. Seems like taking the 2K resistor out of the circuit is the cause for the resulting effect, but what is the reason for it? So, let me know what you were thinking I should try going forward, and I can make a decision if I want to pursue it. Maybe you could give me the concepts and the methodology to use, and I could take it from there and not need to take up your time--when you probably have other projects to focus on. Thanks.
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The attention span thing is not an issue unless if I get into a trouble shooting mode and ask you to try this resistor or that cap and then have to wait 10 days while you order the part. With that kind of delay in response I'm very likely to forget why I even asked to begin with. That becomes very frustrating. I lose continuity if too much time lapses. Turn it around and imagine if you asked a question but didn't get an answer for 10 days.
At this point you need to replace that 2000Ω/10W with a 100Ω/2W (or 3W). This gets the B+ up to a comparable level with the original and also provides a better filtered B+ than the wire jumper. And replace the INT pot with a 1M-L pot. Meanwhile play the unit. Get familiar with how it sounds. Try to describe the reverb issue as best you can. Post a sound clip that demonstrates the reverb issue. Take note if any knob positions will minimize or eliminate the reverb issue. Make sure your footswitch operates properly. Measure and post voltages for EVERY tube pin, even if it's a zero reading.
I'm still here with you.
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Sounds like a plan. I'll try to work up a sound clip/video or something and hopefully the size of the file won't be too big to post.
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I used jumper clips and got the 820 R shorted and took DCV readings for all the pins on the tubes, and its attached.
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Sluckey-I compared my tube voltages with your chart, and they were all really close with yours except for V5, and on that tube all of the readings are around 2 times higher than your readings. Thoughts?
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2 times higher
tells me there's 2X the resistance :dontknow:
maybe power OFF n re-verify with meter the plate n cathode R's for V5
Steve's V5 is an AU7, did you get an AX in there?
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P-1 21.88K / 22K
P-3 45.8K / 47K
P-6 21.66K/ 22K
P-8 40.6K / 47K
So Cathode 8 is a little low, but is that enough to make a difference?
I've been looking at my wiring of the 2.2M resistor with the varistors. Is the way I've wired it in the layout which I've attached OK in order to get the 2.2M R connected to the 47K R and the 0.047 cap going to ground?
Also, is the V-1 Pin 6 to V-5 Pin 2 correct? This was how Sluckey's startup layout for me was done which I followed. He just reversed the layout of Pins 1,2 & 3 with 6,7 & for a more convenient layout I believe.
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is the V-1 Pin 6 to V-5 Pin 2 correct
guessing tubes got re-numbered?
neither schematic shows V1 anything to V5 :dontknow:
I'm not good enough to figure out the DC coupling from the 2 channels into V5-2, or the humidity is melting my brain :laugh:
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We modified the circuit by taking out the Tone Boost part of the circuit that leads from V1 on Pin 1 (switched by Sluckey to Pin 6 in his layout page 2 (attached) for convenience) and eliminating V3A and going straight into V5 at the Pin 2 Grid.
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Okay here's some analysis on the "hum" and "oscillating" issue.
Reverb On/Vib Off-Hum and Oscillation. Changing Vib. Intensity has no effect on oscillation. Vibrato Speed adjustment changes the speed of the oscillation even though Vib is Off.
Reverb Off/Vib. Off-No Oscillation or Hum
Reverb Off/Vib. On--No Oscillation or Hum-Vibrato is fine. Full range of Speed adjustment from very slow at 7 o'clock position to very fast at 5 o'clock position.
Reverb On/Vibrato On--No noticeable oscillation in background. Hum even if Vib is On or Off.
Hum's loudness increases with increase in Reverb Intensity.
Seems like its in the Reverb circuit picking up oscillation even if Vib is turned off from the footswitch.
Remember I'm using a stereo jack for the reverb/vibrato on/off control
What if I jumper the 820K R and take the Vibrato out of the circuit like Sluckey had me do earlier? Seems like it should eliminate the oscillation?
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Okay, so I just jumpered the 820K resistor, and as would be expected no oscillation--because its out of the circuit. There's still hum when the Reverb is On, but no hum when its turned off--and of course no oscillation whether Vib is on or off.
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One more tweak-
Start up with both Rev. and Vib. Off-Then
If Rev. is turned On and Vib. is turned On oscillation will begin after about 5 secs.
Then if you turn Vib. Off, oscillation will stop after about 5 secs.
If Rev. is On, and Vib. is Off, and then turn the Vib On, oscillation will start after about 5 sec.
Hum is present unless Rev. is Off.
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Let's tackle the oscillation problem first. The vib oscillator runs all the time, even when the footswitch is turned off. V4 and V5 are both fed from node B and apparently the oscillator is coupling to the reverb driver through the power supply. The easy way out is to kill the vib oscillator with the footswitch. Make the simple change in the attached pic. This will kill the V4 oscillator with the footswitch so it will have to be plugged in. This is how many popular Fender amps operate. If this is satisfactory then we are done. If not we may need to use separate B+ nodes for V4 and V5.
However, there is always a chance that your layout and/or wiring is the culprit for the oscillation problem.
Do this quick mod and test the operation of the vib and reverb. Let us know.
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Didn't work. I disconnected the wire that runs from the tip on the foot switch jack to where it connects to the turret at the intersection of the 330K and the 47K, and moved that end to the turret where the 820K meets up with the 2 0.01uf caps. I left the connection at the jack alone. Still has oscillation when reverb is on, but now if I turn the Vib Off with the foot switch it emits a loud, static sound and still has some oscillation.
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Sluckey, V4 is served from B Node, but V5 is served from C Node. B Node does also serve V6 for the reverb. The schematic attached is what I went by.
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Didn't work. I disconnected the wire that runs from the tip on the foot switch jack to where it connects to the turret at the intersection of the 330K and the 47K, and moved that end to the turret where the 820K meets up with the 2 0.01uf caps. I left the connection at the jack alone. Still has oscillation when reverb is on, but now if I turn the Vib Off with the foot switch it emits a loud, static sound and still has some oscillation.
Really! So how do you explain this earlier statement...
Okay, so I just jumpered the 820K resistor, and as would be expected no oscillation--because its out of the circuit. There's still hum when the Reverb is On, but no hum when its turned off--and of course no oscillation whether Vib is on or off.
Both of these puts a ground on the junction of the 820K and the two .01 caps. Both will kill the oscillator. Of course the footswitch should kill or enable the oscillator. I wonder if your footswitch jack is wired properly? Show me a pic of your FS jack.
Try this ... Completely remove the vibrato wire from the foot switch jack and the board. Do you still have oscillation in the reverb when the INT pot is turned down? Does the reverb footswitch operate as you expect? Did you use a proper shielded cable for the foot switch as we discussed a long time ago?
Sluckey, V4 is served from B Node, but V5 is served from C Node. B Node does also serve V6 for the reverb. The schematic attached is what I went by.
My error. I meant V4 and V6 share node B.
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Sluckey--Here's the photo. Its the white wire that's connecting from the tip (nothing changed here and it turned on/off the vibrato fine) and then it now connects at the base of the turret where the 820K is. I have to believe the foot switch jack and foot pedal are fine because it was working fine before this change. Agreed, jumpering the 820K turned it off. Now, it has loud static that wasn't before. That's all that was done. I've had an evening cocktail, so I'll wait until the morning to remove the Vibrato wire as you suggest. Thanks for your time. Best. Stephen
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Here's a thought. If you look at the last layout that I uploaded, today I think, you can see that I grounded the footswitch jack, the 820K resistor, Pin 8 of V-4 tube, and the Reverb input and output jacks to the same Ground Lug screwed to the chassis. Could that be the problem?
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Sluckey-I failed to respond to your question about using the shielded cable. I used it where you suggested. The only instance where I grounded the shield was at the input jack, and I didn't ground the other end of the shield. In the other instances where I used the shielded cable, I just cut back the shield and didn't ground either end, and just used the lead, after covering the wire with shrink tube. Is that correct?
I haven't started working yet on your follow-up suggestions. I thought I'd wait until you see my comments from last night about my grounding. Since the static noise started after moving the wire coming from the Vib tip over to the 820K R, should I move it back to its original location before I start changing anything else?
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In the other instances where I used the shielded cable, I just cut back the shield and didn't ground either end, and just used the lead, after covering the wire with shrink tube. Is that correct?
No. In order for the shield to be effective, you must ground one end.
Since the static noise started after moving the wire coming from the Vib tip over to the 820K R, should I move it back to its original location before I start changing anything else?
yes
I'm really concerned about your layout in the vib/reverb area. The wire to the reverb footswitch is very sensitive and there is a lot of other wires in close proximity. I'm beginning to think this may be how the vib is coupling into the reberb.Plus the FS jack is located in a noisy location. I'm gonna look at your layout this morning and make some suggestions that only involve rerouting some wires.
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Thanks. Maybe the issue relates to my failure to use the ground on the shielded cable. I'll re-work those wires, but will wait to see what you suggest before I do that.
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I used shielded cable without connecting the ground shield in 3 instances:
V-7 Pin 2 to Rev. Output
Rev. Jack Ring to 0.047uf cap
1uf cap. neg. to Rev. Input
The only other use of shielded cable was with the cable from input jack and I did ground the shield there.
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Sorry if this misses the point but if you get tremolosignal into your reverb you probably already checked your tank (shield) is connected to the chassis (shield) like it should?
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Could you clarify for me how it should be wired? I could have missed something. I know that I didn't ground the shielding in the shielded cable connecting the jack coming from the tank's output jack that goes over to the V7 grid Pin 2. So that's something that needs to be done. That jack is grounded to the chassis though.
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Sluckey, Shooter, et al--Maybe I found something. The .047 cap connects on V-7 P1 plate, and then I ran a wire from the cap directly to the Reverb tip jack connection. Then I ran another wire from the Reverb tip jack on to the Reverb Intensity pot. In looking at the schematic, it might have been better if I ran the wire from the .047 cap directly to the Reverb Intensity pot, and then picked up from there and ran the wire to the Reverb tip on the jack. Thoughts? If this is better, should either of those wires be shielded?
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That's one of the things I wanted you to do. Run a shielded wire directly from the reverb pot to the .047 cap on the board. Connect the shield to the ground lug on the reverb pot. But for now, don't connect a wire from the .047 cap to the FS jack. You can add that after we get the oscillation issue sorted.
Does this help?
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I removed the wire from the 820K R and returned it to as before, and now the static is gone. I also re-wired as I described above without using shielded cable either when going from the 0.047 to the Reverb Intensity pot or from that pot to the foot switch Reverb jack connection, and the oscillation remains, but maybe not as strongly. So if you can tell me which connections need the shielding done correctly let me know and I'll give that a try.
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Sluckey-Ok, I'll wire as you suggest. So for the time being there will be no connection to the Reverb ring on the footswitch jack at all?
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Did the re-wiring but still has oscillation. There is no wire connected from the pot to the foot switch jack. So the reverb is on and can't be turned off. Same symptoms as before. The oscillation does vary directly with changes to the Vib. Speed pot.
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Read reply #395
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There is no wire from the cap to the foot switch, just from the cap to the pot and it is shielded and grounded. And there no longer is any connection to the Reverb at the foot switch. Before these changes the wiring went: Rev foot switch, to cap, to pot, to foot switch with no shielding in effect.
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There is no wire from the cap to the foot switch, just from the cap to the pot and it is shielded and grounded. And there no longer is any connection to the Reverb at the foot switch. Before these changes the wiring went: Rev foot switch, to cap, to pot, to foot switch with no shielding in effect.
And that's what I wanted. We'll use this as a starting point. Now just remove all wires from the footswitch jack, including ground wires and the vib wire to the 820K. I'm trying to clean up that tangle of wires around the FS jack and reverb jack. Try the amp like this. Then use3 a gator clip test lead to connect the 820K resistor to chassis. Report back.
Then tomorrow am when I'm rested we'll begin trying to track down the source of the oscillation.
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Still hum and oscillation. Before doing anything, I removed the foot switch pedal from the jack, and had the hum and oscillation. So I then un-soldered the 3 wires connected to the foot switch jack, one wire each at the tip, ring, and ground, and left them safely suspended from the board. Turned it on, before jumpering, and still the same hum and oscillation. So then I jumpered the 820K between the chassis and the ground side of the resistor. Same thing. I also jumpered it on the other side of the resistor where it connects with the two .01 caps. Made the loud static sound. So it seems that its not related to the wiring at the foot switch jack. I'll defer to you on the next step, but was wondering about the V-7 Pin 2 grid connection to the Reverb jack coming from the Output of the tank and into the board? I just unplugged the RCA jack going into the board from the Ouput jack of the reverb tank and NO HUM or OSCILLATION. Of course there's no signal going to the board, so maybe that doesn't mean anything. But it clearly means its the signal from the tank to the board that causes the problem. I have a 4FB3A1B reverb tank and both of its jacks are GROUNDED. Could that be the issue?
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I saw this thread and thought it might be relevant:
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Re: need some help with nasty parasitic oscillation
« Reply #13 on: January 25, 2017, 10:40:57 pm »
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Quote from: markmalin on January 25, 2017, 07:04:06 pm
The tank I bought has input isolated and output grounded. The jacks I bought are panel mount RCA's Fender style, so they are not isolated from the chassis. Without the jacks isolated, could that possibly cause a ground loop?
No, that's why 1 of the tanks jacks is isolated. (1of the tanks jacks has to be grounded so the tanks chassis acts as a shield.)
If both of the tanks jacks were grounded and both of the chassis jacks were grounded then there would be a ground loop.
« Last Edit: January 25, 2017, 10:45:59 pm by Willabe »
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I just unplugged the RCA jack going into the board from the Ouput jack of the reverb tank
for fun;
put the output jack back
remove the INPUT to the tank and ground the***tank*** center pin, effectively grounding everything to the right - still hum osc?
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The oscillation you are experiencing is not parasitic oscillations. It's the vibrato oscillator coupling into the reverb circuit. That's why when you shorted out the 820k to kill the oscillator, the oscillations went away. This is not related to the reverb hum.
I still can't get past the idea that you can put a jumper across the 820k resistor (thus grounding the top side of the 820k)and kill the oscillation, but you can't connect a gator clip test lead to the top side of the 820k and chassis ground without causing all kind of nasty sounds. Makes no sense at all unless something is amiss in your grounding scheme, which BTW, is a mess. In fact, the entire board layout on the left end is a bit crazy. I suspect layout and grounding are big contributors to the issues you have.
If you can get to the point of being able to kill the vib oscillator by grounding the top end of that 820k, then we can move the FS to that point and eliminate the vib oscillation from getting into the reverb. Unfortunately, I don't think I can do that without putting my hands on the unit, and I'm not in that line of business. So, it's up to you.
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Shooter-I have the output of the tank connected to the board. I removed the input to the tank from the board and jumpered the center pin on the cable going to the tank input to the chassis, and it has the same Hum and Oscillation. So unless I misunderstood your instructions, no solution--same problem.
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Thanks Sluckey-I'll work on the 820K issue and see what I can figure out. As long as the reverb output is not connected to its RCA jack on the chassis, the Vibrato is perfect, and no hum and no oscillation. Its perfectly quiet. Do you think the transducer for the output should be de-soldered so it's open and not grounded?
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The schematic shows that the vibrato signal is being injected into the circuit at jumpered grid pins 2 and 7 on the V-6 reverb tube, and the signal with the vibrato is passed along from there through the tank, and out, unless that part of the circuit is bypassed with a dry signal avoiding the tank. There is no background oscillation when the reverb is off, ie. "dry", so that part of the circuit must be okay. So the background oscillation must be "magnified" so that it becomes audible somewhere between the 1uf cap coming off of the V6 plates and the Reverb Intensity pot because manipulating that pot affects the loudness of the background oscillation. I notice in my layout that I ran the wire from the V-7 Pin 3 to the 2.7K, as on the schematic, but then instead of taking the other end of the 2.7K directly to ground, I daisy chained it with the .047uf, 330K's etc. in the V-4 circuit to get the 2.7K from V-7 to Ground. Could that be the problem? Should I just go directly to Ground from the 2.7K? Maybe that's what's picking up the background oscillation?
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There is no background oscillation when the reverb is off, ie. "dry", so that part of the circuit must be okay.
That could be a big clue. So, the vib may be coupled into V6, or the tank, or V7. But is it coupled through the shared B+ node, or ground connections, or layout?
Try moving the reverb tank around to see if you can eliminate the vib oscillations.
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I physically moved the tank around at all angles and the oscillation remained the same.
I looked at the layout and Node B is being shared by V-4 and V-6, and the way I connect the 270K and the 47K on pins 1 and 6 on V-4 is by jumpering the 47K with the 5K 10W which goes to V-6 and also to the Reverb Input! This looks like an issue. My wiring goes from Node B, to 270K (vib. circuit) then a wire from there to the 5K (reverb circuit) then by jumper to 47K (vib. circuit). What if I removed the jumper between the 5K and the 47k, and then went straight from Node B to 5K, and ran another wire straight from Node B to 270K then from it to 47K? So there would be separate wires supplying B+. Thoughts.
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Well, I tried that and no difference. I'll keep looking.
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I just changed the grounding I was thinking of in #408 for the 2.7K resistor so it now goes directly to the Ground Buss, but no change. So that's not it.
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As for the 820K resistor, when I jumper it with test cables, the oscillation is gone but it has a loud static hum. Even though its going to ground, there are still other components in the circuit that are still connected. In fact the B+ from the B Node is still feeding that component via the 270K, the .02 and the .01 caps.
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the 5K 10W which goes to V-6 and also to the Reverb Input!
There better be a 1uF cap between the 5K/10W and the reverb input!
Try this... Completely remove the 1uf from the board. This will totally kill the reverb. Does this kill the vib osc?
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Nope, oscillation is still there. If I disconnect the tank, the oscillation stops. However, if I connect the input and output reverb jacks together with one of the cables, the oscillation is back and a bit louder.
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If there's nothing going into the tank's input jack (and the only connection to the input jack is the cable at the turret where the 1uf was located), then the signal has to be getting into the tank from the output jack.
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Leave the 1uF disconnected for now. Reconnect the tank cables as normal. Now use a gator clip test lead to ground the reverb output jack. Does this kill the vib osc?
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Clip 1 end of the lead to the chassis, and the other end of the lead to the ground lug on the output jack?
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Doing it as I describe above, the oscillation is still there and now it has some static in the hum.
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So I disconnected the Reverb Intensity pot from the lead coming off of Pin 7 on V-7 and the oscillation stopped. Still a hum. However, the volume through the speaker was much lower, and now there was no vibrato at all.
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Well I re-installed the Reverb Intensity pot going to the grid of V-7, and its back with its hum and proper volume levels. Seems to me that the hum is created somewhere between the tank's output jack and the reverb intensity pot. There's not much to check there and I've done it and don't find any issues. So the only thing I can think of is to change the transducer bridge on the output of the tank so that it is no longer grounded by removing the solder bridge. If there's no change then I can always solder it back. But that's for tomorrow.
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Hope everyone has a great July 4th!
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I have eliminated the transducer in the tank theory without de-soldering the joint. I just unplugged the cable at the output jack on the tank and left it plugged in on the chassis and the background oscillation continued. I also have determined that the volume of the oscillation is controlled by the Reverb Intensity pot. Neither the Main Volume pot nor the Vib. Intensity pot have any effect on the volume. The Vib. Speed pot does affect the speed of the oscillation. The Output Level pot will increase the volume of the oscillation but it is limited by the Reverb Intensity pot setting. So that satisfies me that the cause lies between the Reverb Output jack and the Reverb Intensity pot.
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Could it be possible that the background oscillation signal is being "syphoned" back through the V-6 tube and along the Dry Signal path into the V-7 C Node part of the tube, and the setting on the Rev. Intensity pot on Pin-7 is controlling the amount of the "syphon" effect leaking it to the Main Output jack going to the amp?
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So that satisfies me that the cause lies between the Reverb Output jack and the Reverb Intensity pot.
I agree. I want you to connect another large filter cap in parallel with that 1µF cap at node E. Use a 10uf, 20uf, 30uf, 40uf, whatever you have. Any better?
edit... If you don't have any filter caps then put a jumper across the 10K that's between node D and E. This will short those two nodes together. Any better?
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I didn't have any caps with enough V protection so I jumped the 10K. Its very much quieter, but still there. Sounds like progress.
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Sluckey-any thoughts on how I should proceed given this positive result? Any ideas on the reason for what's going on? Do you think its related to the fact that I don't have an Phase Inverter and output transformer in this design that might otherwise act to prevent this? Thanks.
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Would there be any benefit to putting a resistor on the V-7 tube at Grid P-7 to ground?
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Any ideas on the reason for what's going on? Do you think its related to the fact that I don't have an Phase Inverter and output transformer in this design that might otherwise act to prevent this?
I think it's either layour or a poor solder joint somewhere. You don't need a PI and OT to prevent this.
Would there be any benefit to putting a resistor on the V-7 tube at Grid P-7 to ground?
It's OK to just go ahead and try something when you have an idea. However, there is already a resistor from V7-7 to ground. Adding another one is not likely to do anything.
Try this... Ground V7-2 with a clip lead connected directly at the socket and chassis. Any better?
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I un-jumped the 10K and jumped from V-7 P2 to chassis and its about the same. Still quieter than without being jumpered. I have found though that if I turn the Vibrato Intensity all the way up that the oscillation stops! Its there until that final minute turn of the pot. I'm getting the linear pot today, so I may try that. Should I still go ahead and replace the 1uf Node E cap with a bigger one? I'll also be getting the smaller R for the Node A-B connection and will remove the existing 2K 10W one which is currently just being jumped.
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Should I still go ahead and replace the 1uf Node E cap with a bigger one?
yes. I had to do the same with my M2 to eliminate some different bad behavior. The original used a 0.1µF at node D. I replaced it with a 47µF. Look at the schematic, lower right corner.
http://sluckeyamps.com/lil_maggie/Magnatone_M2.pdf
Meanwhile, unplug your footswitch, set it aside, and don't plug it back in until I say. Does this kill the oscillation?
Then we will revisit reply #382 and stay there until we can successfully kill the oscillator by grounding the top side of that 820K resistor.
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You've probably forgotten that you had me totally un-wire the foot switch earlier on. So nothing is connected to it and nothing is plugged into the jack. Those 3 wires are just free in the air. Also, you had me remove the 1uf cap totally at the V-6 P1-6 connection to totally take the reverb out of the circuit at that point. So its still oscillating except when the Vib. Intensity pot is turned up alllllll the way. Back off a hair and it returns. I ohmed the 820K and its reading 817K (actually my meter is in auto mode and its reading 0.817Mohms). I just jumpered the top side of the R to the chassis with a clips and still makes really loud static noise. So nothing has changed from when we started, ie. the 820 is still acting the same way.
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I just jumpered the top side of the R to the chassis with a clips and still makes really loud static noise. So nothing has changed from when we started, ie. the 820 is still acting the same way.
Use that same clip lead to just short out the 820K, One clip on each lead of the resistor. Does it kill the oscillator?
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No luck. Still makes the loud static noise, same as if I connected the top end of the R to the chassis. The static is so loud I can't tell if its oscillating.
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No luck. Still makes the loud static noise, same as if I connected the top end of the R to the chassis. The static is so loud I can't tell if its oscillating.
Remember this from reply #380?
Okay, so I just jumpered the 820K resistor, and as would be expected no oscillation--because its out of the circuit. There's still hum when the Reverb is On, but no hum when its turned off--and of course no oscillation whether Vib is on or off.
I don't think your test lead is any good or you are not getting a good connection. Check the end to end resistance.
Cut a fresh piece of wire. Solder one end to the top side of the 820K. Solder the other end to the negative lead of the Node B cap. Does this kill the oscillation?
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The test lead is reading 0.2 ohms across it, so its fine. I went ahead and soldered a wire as you said and still the same result. The result is that it creates a very loud screechy scratchy staticey noise. I can't hear any oscillation but the noise may be covering it up. If what you are expecting is a relatively quiet sound with maybe a little noise or hum, then that's not what's happening.
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I only see 1 820K R in the whole schematic and that's where the V-4 Tube is. So that's what I've been checking.
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I'm expecting to kill the oscillator without introducing any noise.
OK. Leave the wire connected to Node B cap negative lead and totally remove the 820K from the board. Connect the wire to the turret where the top side of the 820K used to be. Any luck?
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I'll give it a try. Attached is a pdf image of just that section of my layout that we're working with. This is how its wired. Any problems with it?
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Same noise as described above. Nothing different than when the resistor was still in the circuit.
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OK. Leave the wire connected to node B cap but remove from where the 820K was connected. We'll be using that ground wire again. So, the 820K is still off the board. Any noise? Oscillation gone?
BTW, the partial layout you just posted is a bit different form the one I'm using. Please re-post the layout that is exactly like your wiring.
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The layout is basically the same, I just separated the B Node into separate wires, but this part of the circuit hasn't changed. Attached is the current full layout from which the last "focused" image was posted. Okay, good news I guess. I disconnected the ground at the turret, leaving it soldered to the Neg. B Node, and the sound is clear with NO OSCILLATION but some hum. But not loud static etc. like before when I jumped the 820 K.
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Oh, and of course there's no vibrato anymore since the circuit has been broken.
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OK. Put the 820K back on the board. Cut that black jumper between the bottom of the 820K and the 3.3M. Move the green ground wire from the bottom of the 820K to the bottom of the 3.3M. This will leave nothing connected to the bottom of the 820K but we are about to change that.
Connect a new wire to the bottom of the 820K. Connect the other end of this wire to the VIB lug on the FS jack. Now use your test lead to short the FS VIB lug to chassis. Shorted will enable the VIB. Remove the short to kill the VIB. Test your Vib and reverb operation. Is all OK?
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Thanks. Sorry for taking so much of your time.
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Do you want me to re-install the 1uf cap at the V-6 P1-6 connection that you had me remove previously? I also just received the replacement 100 ohm 2W Resistor for the 2K 10W at the Node A-B connection that is currently jumpered. Should I install the replacement Resistor at this time?
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yes and yes
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Ok, got it re-wired as directed and replaced the R at A-B Nodes with the 100 Ohm one. I jumpered the VIB footswitch and it turns on and off the Vibrato. Still has background oscillation which stops when I take the jumper off of the chassis. Only issue is now I'm not getting any Reverb at all!
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Look over everything that's been done and/or undone while you tracked down where the osc was getting into the reverb.
Measure and post voltages on V6 and V7.
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Here are the VDC with the Vib disconnected and the 100 ohm R installed at Node A-B:
V-6:
P1/6-217.1
P2/7-37.5 mv
P3/8-5.92
V-7:
P1-121.3
P2-.2 mv
P3-1.284
P6-186.7
P7-1.3 mv
P8-1.940
I'm checking on the wiring.
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Ok, got it fixed. The problem was at the reverb output jack. I had a shielded cable going from V7-P2 to the output jack for the reverb but had not connected the cable's shield to ground. So I tried to fix that by connecting the ground shield in the cable to the ground lug on the output jack. The problem is that I have the 47K R connecting the ground lug with the tip lug of the jack and that created a short. So I disconnected the shield, and now it works. My question though is how do I ground the shield? Wouldn't it cause the same problem even if I connected it to another ground point?
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The problem is that I have the 47K R connecting the ground lug with the tip lug of the jack and that created a short.
That's not the problem. I suspect the shield is shorted to the center conductor, probably at one end of the cable. Check the cable with your ohm meter. Looks like you are using RG-174 cable? It's very easy to melt the insulation of the center conductor when soldering the shield. Just use another piece of cable and be careful. I quit using 174 for that very reason.
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You were correct. Should I use shielded cable for this connection, and do it over, or just use regular wire for now?
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Try it with a regular wire. A shielded cable would be better. I would use shielded it it's over 2-3 inches long.
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It was about 4" so I ran another shielded cable and seems to have worked this time with no short. So now I've got reverb, and I've got vibrato oscillation that will stop if I disconnect the jumper from the chassis, and then it leaves me with a scratchy background sound with reverb still operational. I guess I'm ready for the next step.
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Reconnect the stuff to the FS jack and test the footswitch.
And recheck the voltages on V5 pins 1, 2, 3, and 6, 7, 8. Also recheck the voltages on all the filter caps. Post your findings. And give me the model number for your PT. I've put together a one page schematic for you, complete with your voltages. Makes it easier to see the flow when it's all on one page.
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I reconnected the foot pedal wiring. I did not connect the original wire going from the 47K to Vibrato since you have the new wire that was added to control it. The foot pedal responds as it should. Let me know if you want me to reconnect that other wire to Vibrato. Below are the voltages.
V-5
P1-234.2
P2-155.0
P3-159.0
P6-241.6
P7-211.3
P8-208.9
The Caps VDC readings are as follows:
A-329.4
B-325.8
C-308.8
D-276.7
E-250.0
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The PT is the Hammond 269JX.
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In comparing the voltages of my V-5 with yours, mine are significantly higher for both sets of grids and cathodes. That tube's output leads to the V-6 for the reverb. Do you think the background oscillation could be due to the fact that my voltages are so much higher for some reason than yours? Is there a way to drop the voltages on my V-5 grids and cathodes? Would a change in the 47K resistors on the V-5 have any effect?
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V5 voltages are not an issue. You cannot compare my V5 voltages to yours because you removed V3 from the preamp. V5-2 is direct coupled to the V3-6 plate in my amp, but it is directly coupled to V1-1 plate in your amp. V1 plate is higher than V3 plate. And that higher voltage directly couples to V5-2 and that higher voltage causes the other V5 voltages to be higher. No further action needed for V5. It's OKAY.
Do you think the background oscillation could be due to the fact that my voltages are so much higher for some reason than yours?
I hope you don't have any background oscillation now. The only time you have oscillation now is when you turn on the vibrato footswitch and that should put the oscillation in the foreground because you want to hear it.
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I guess what I'm trying to describe is that if you have the vibrato on with no reverb, and you're not playing anything, everything is quiet. However, if you have the vibrato on and you turn the reverb on, and you're not playing anything, you hear oscillation. Seems to me that it should be quiet too. That's why I was thinking that if the V-5 is getting more voltage maybe that's emphasizing the background oscillation. If I turn down the reverb intensity pot then the background oscillation is quieter, but then of course there's less reverb. Is it that way it is in your M-10A amp too? If so, then that's fine. And of course its not noticeable when you're playing.
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I haven't had my amp plugged in for over 5 years. Don't remember.
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Why not plug it in and give it a test? It probably misses you! Haha!
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It's sitting in a room with about a dozen other amps that don't get played these days. They have to entertain each other. :laugh:
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Sluckey-Well its sounding great. Your fix worked perfectly. Thanks again. I got the 1M Linear Pot and installed it for the Vibrato Intensity to replace the Audio pot I had used, and I like the Linear pot much better. I have more control over the vibrato effect volume. I've taken off the test gnd lead that you had me add, and also removed the original wire going from the 47K to Vibrato since you have the new wire that was added to control it. I guess the only other thing that came up was putting in a larger Node E cap to replace the 1uf 450V that's presently installed. What are your thoughts, and what would the result have on the sound, etc?
If I can figure out how to upload a video or sound file that's small enough to upload to this thread, I'd like to share the results with everyone. Looks like this thread is winding down with a successful outcome. Thanks again.
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I thought I would upload an As Built layout in pdf and DIY files of my Sluckey M10-Reverb/Vibrato modified build that I successfully completed, along with his schematic. Really pleased with it. I having a cabinet built by Guitar Cabinets Direct and hopefully that should arrive this week, and I'll send photos when the chassis is installed. I also am working on a sound recording so you can hear that this device actually does work, and sounds great. Thanks again for everyone's help with this project. Stephen
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Attached are photos of the final build in the cabinet that was made by Guitar Cabinets Direct. They did a great job and were very prompt.
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I've got 2 more photos. Here's one of them.
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Ok, here's the last photo.
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Ok, well I made a short recording of a few bars of Ray Charles' song "What'd I Say". I certainly haven't done him or the song justice, but I'm just starting to play again. Anyway, enough excuses, I recorded it without any effects, then added the Vibrato, and finally the Vibrato and Reverb so you can see how it sounds. Vibrato Speed is at about 10 o'clock position, and Reverb Intensity is at about 8 o'clock position. Volume and Treble are at 12 o'clock, and Bass is at 2 o'clock. Thanks for everyone's help.
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Sounds good. Now you need a big amp. :icon_biggrin:
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Yea, I was using my 5F1 amp. I should have used my 1966 Gretsch Variety Plus amp with 35 watts output. It’s about ready for a re-cap job. Thanks again.
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Would you say this project has met your expectations from your original post?
I've attached a reformatted schematic that you may find useful. It can be printed on one sheet of legal size paper.
Edit... Removed attachment and added it below.
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Sluckey--Thanks so much-This is great--Yes, there is no doubt for me that this project came out exactly as I had hoped for. I've never heard any Magnatone in person, and I don't think I've ever heard a Mag 10A even on YouTube or elsewhere, so I don't have anything to compare mine to, but it certainly has the distinctive Vibrato effect that I was looking for, and the reverb is a bonus. I have read a little about "reverb dwell" control, but I'm not sure I know what that does, so I don't know if that would be anything I would want to add. I think I've seen folks running a 1M pot off the Grid of the V7 tube in place of the 47K resistor. And if that's correct, it would be easy to do, but I don't know what the result would be by way of sound. In looking at your schematic I noticed that you have a date of "2010" in case you want to change that to "2020". Thanks so much for all your time and help. Best. Stephen
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I don't see any viable way to add a dwell pot to the maggie circuit. Dwell is used to control the level going into the tank. It is usually implemented by replacing the 1M grid resistor on the driver with a pot. But that would also affect the dry signal in that circuit and that's not good. I've updated the new drawing (pun intended).
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I haven't seen many amps with dwell pots, so its probably something that doesn't make much impact on the sound. I'm happy just the way mine is! Best.
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> add a dwell pot
Split the 12AU7. This *will* need tinkering to get the relative gains acceptable. (I suspect this is way too much gain on the drive side; a AUDio taper dwell pot may be best for initial testing so you don't have to turn-down to the 0-1 crack.)
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Split the 12AU7.
He's still in the "I can't quit playing, or believe it works faze" :icon_biggrin:
Maybe in a month
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Shooter my exact words to my wife who was with me when I fired it up were "F*** I can't believe it works!" And I said it again!! So yes I'm still in that stage but will keep this in mind if I want to pursue it.
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:thumbsup:
You ignored "time" and focused on the task at hand
my last build I gave Pam $100 and said, I'm gonna be making noise for awhile today :icon_biggrin:
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Here's a question for you guys. I've been playing the VibroVerb (not yet Trademarked) through my 5F1 Champ (5 watts), and I set its Output level which controls the "output" at the output jack, to about 9 o'clock on the pot. Sound volume is fine. Today I decided to run it through my Gretsch/Valco amp which has 35 watts output. When I did that I had to turn up the Output Level on the VibroVerb to about 3 or 4 o'clock to get equivalent volume. So for some reason it seems that the input sensitivity on the Gretsch is not as high as on the Champ. Am I interpreting this correctly, or does anyone know the reason why I have to increase the Output Level so much more. Thanks.
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The 5F1 hi input has no voltage divider at the input but the Gretsch amps often have a voltage divider at the input jacks. Show us your schematic and we can be more specific.
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Thanks. Here you go. I have the 6165 model. I'm pretty sure this is the schematic for the preamp section of the amp. There's another schematic for the power amp. I'm plugged into the "dual input".
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You need a stereo plug to use the dual input jack properly. Plug into the channel 1 input.
But really, it's just a matter of different input voltage dividers. Nothing wrong. That's why there's an output level knob. :icon_biggrin:
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Sorry, I see I posted the wrong schematic last night--I posted the Power Amp. Attached is the schematic for the pre-amp. I don't know if this helps.
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Yes, it looks like when I use the Dual jack input on the Gretsch, as I always have, with a regular phone plug, which I always have, the input from the guitar/Vibro-Verb is going through the 470K Resistor to GND rather than the 1M Resistor if I had used the Input 1 or had a Stereo plug. The 5F1 Champ's input goes to a 1M resistor, so that probably explains it. I'll switch inputs and let you know the result. Thanks.
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The idea of the dual input jack is to send the guitar signal through both channels. But if you use a standard plug channel 1 input gets grounded out and the signal only goes through channel 2. Easy fix. Just put a stereo plug on your input cable and jumper the tip and ring together. (The stereo plug will still work with a normal input jack.) Then you can use both channels and all the knobs. The M-10A does the same thing but calls that jack a stereo input.
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Well I think I figured it out, and the result is that the Output in decibels is in fact the same. I download a Decibel App to my Ipad. Then I plugged the guitar directly into the Gretsch Channel 1 jack and measured the Decibel level at around 64 when I plucked the E string. Then I plugged the guitar directly into the 5F1 #1 jack, plucked the E string and adjusted the volume on the amp until it also showed a level of about 64 Decibels. So now the amps are set at the same output level. Obviously the Gretsch that's 35 watts with 2 12" Jensen speakers has a lot fuller sound than the 5F1 with 5 watts and a 8" speaker. So then I plugged the guitar into the Vibro-Verb, and then connected it to the Gretsch. I turned the Output Level all the way up on the VV and after adjusting the Treble and Bass on the VV to get a similar, but richer, sound as the 5F1, I got a reading of about 64 Decibles. To finish the test, I then plugged the VV output into the 5F1 without changing any setting on the VV, and also read about 64 Decibles. Although the sound was not as full and a bit brighter/tinnier on the 5F1, the actual sound levels were pretty much the same whether I played directly through either amp, or through the VV--as long as its Output level was turned all the way up. When I plugged the guitar into the dual input jack on the Gretsch the decibles were just a little bit lower, around 60 or so. If you lowered the Output Level setting, then of course the decibel level would be less than if it went straight from the guitar to the amp. Although my 1965 Gretsch amp that I purchased new has some years on it, it is still original except for 1 filter cap replacement, and a replacement to a 3 prong plug. Still original tubes. Thanks again for the help.
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Question for you about my Gretsch pre-amp schematic shown in my reply #485 above: What are the VR1, VR2 and VR3 components shown on the V2 and V3 tubes, and what are their values? Since I've been playing the Gretsch amp more its really begun picking up more hum than normal. I guess components are starting to fail--it is over 50 years old! When I have the guitar plugged into Input 1 it has the hum which goes away when I unplug the guitar or turn the volume down/off. Ideas on where to look? Could it be the 35uf cap coming off the cathode on V2 Pin 8? Thanks.
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What are the VR1, VR2 and VR3 components shown on the V2 and V3 tubes, and what are their values?
Those are voltage dependent resistors, AKA, varistors. Their resistance changes depending on the applied voltage. You need a part number if you're considering replacing. Not likely to find one. I'd leave them be.
When I have the guitar plugged into Input 1 it has the hum which goes away when I unplug the guitar or turn the volume down/off.
Probably nothing wrong with the amp. Can you kill the hum with the volume control on the guitar?
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I thought they might be varistors like I'm using in the Mag 10 A vibrato circuit. Neat. Yes, I'll leave them alone. But now I know what they are. The volume control on the guitar has no effect on the hum from the amp. With the guitar unplugged, I hear a higher pitched tone or hum coming from the amp. When I plug the guitar in, I still here the higher tone, but then I also hear a low hum so I'm getting both types of noise when the guitar is plugged in, and the level of the noise varies with the Volume control on the amp and will disappear when the volume is totally down to 0 level. I hear it from both of the Channel 1 inputs, but a bit lower on the "dual" jack (I'm still using the mono plug). Same effect on the Channel 2 Bass channel, but a bit lower in volume.
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Have you ever changed filter caps in that amp?
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Nope.
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I decided to check the caps in the power supply and wanted your thoughts on the results.
I have a Blue ESR Tester, and all of the results seem to appear fine. I connected 1 lead to chassis ground and the other to the + side of the caps and took the readings.
The can cap w/ 20-10-10 at 450 v read ESR's of .80,.98, and 2.4.
The single 20/500v which was replaced a few years ago read ESR of .95
The single 35/50v which was replaced at the same time with a 47/160 read a ESR of .57.
So with these ESR readings is there any reason to replace these, or is there another test I should do?
Thanks.
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I've never measured cap ESR. I usually replace filter caps based on hum, decoupling issues, or ripple voltage measurements. If this is an amp that you rely on for gigging, I would replace the filter caps based on age just for reliability, but for a home amp, I would not bother.
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+1
never done esr either, ripple voltage and age are 1 n 2, if you're bored, watching each tap on a scope + meter while driving amp hard/soft/hard/soft can be fun :icon_biggrin:
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Yes, I'm a bit bored right now, but I don't think I want to take it to the next level and learn how to use a scope! I'll rely on you guys!
Speaking of which, I was going through the Gretsch's pre-amp to ID the caps to replace, and it has two caps that I don't know if they're electrolytic or not--I'm assuming they're not, but I'd like your input.
They're 1uf 400V, they have the name "Standard" on them, and they have a black ring at one end. They appear to be paper, and not a metal shell, and don't have an indent in them like the other larger electrolytics in the amp. One of them is connected on one end to the Vibrato footswitch tip, and the other end connects to the Plate on the 6DR7. The schematic I have isn't real clear, but I think the other one is coming off the Cathode, pin 8, on the 12AX7 for the Reverb recovery and going to GND.
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They're 1uf 400V
"most" of the time when a cap =>1uf it's an Ecap. There are non-polarized but typically in HIFI not guitar
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They are most likely electrolytic although they don't have to be. If your tremolo and reverb are working fine I suggest you leave them alone.
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Thanks. Good point.
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Well I've satisfied myself that the caps are all okay even though they're old. It looks like I've got an issue with my vibro/verb creating some distortion. It has just started, and it doesn't matter if the signal is processed or if its clean when it goes through either of my 2 amps. I notice it worse on the G string. Really sounds buzzy. I thought my strings were bad, or they were hitting on the fretboard, but I plugged them, ie. the Gretsch CG and the Strat guitars, directly into the amp, and the sound is clear. So any ideas on what could be causing this? I tried adjusting the Output Level, as well as the Treble, Bass and Volume, but they didn't have any effect on the buzz. Thoughts?
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No ideas.
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Looks like it was a tube. The V6, 12AU7 was making intermittent noise when I tapped it. I replaced that with one a friend had, and it seems to have cleared things up.
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As I've played with the effects unit, I've got a couple questions for someone. I notice that if I turn on the reverb and the vibrato, and then disconnect the stereo footswitch that controls these effects, that the Vibrato stops but the Reverb stays on. If I then reconnect the footswitch, then the Vibrato comes back too. Why wouldn't they both deactivate when the plug is removed from the jack?
Second, I get a lot more treble than I would like, such that if the treble control is set much more than at about the 8 o'clock position, that it starts to get gritty. I'm using 1M Audio/Log pot per the schematic. Would a different pot or cap/resistor setup be an option? Thanks.
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The Vibrato needs a ground to enable the oscillator. Since the footswitch provides that ground, it must stay plugged in. The reverb needs a ground to disable the effect, so it will still work with the switch unplugged. This is the same behavior that all the Fender AB763 amps exhibit.
As long as you can get a usable tone from the unit I would not be concerned with what number the dial lands on.
You probably have the only one of this Vib/Rev unit. That makes you the expert. :icon_biggrin:
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Thanks. After I posted my question about the reverb I noticed that it didn't matter whether or not I had the reverb on or off, and that in either situation when I unplugged the footswitch plug the reverb is ON. So I guess its working properly. Thanks again. Stephen
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If you want to be able to use vibrato and/or reverb without the footswitch, then replace the jack with this one...
(https://hoffmanamps.com/MyStore/catalog/images/IMG_2288.jpg)
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I'm trying to figure out how to set the VV so that the signal strength going out and on to my amp, is at the same level coming in. I assume that would give me a flat response. Right now the VV is unplugged and the caps are drained, and the switch is OFF. I plugged the guitar into the Input jack, and have my DMM set to AC and clipped leads to the tip and ground of the input jack and strummed a bit. It varied of course but read on the average around 0.035mv AC. If what I did was correct, how do I read the value at the Output Jack? Do I do the same thing but plug it in and turn it on? And of course only touching the guitar? I assume by adjusting the Output Level Pot, I could adjust the reading until they are the same. I'm not totally crazy, I promise. Thanks.
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:icon_biggrin:
crazy has many forms
I do the same, only with a scope. you're looking for relative so put a jack in the output, clip your meter and check.
.035mVac is pretty small for a signal, 20mVac is about as small as most amps can "see" at the input.
I use a signal source (with volume), I pick an amplitude, verify, then jack in
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Guitar is a terrible way to try to match input/output voltages.
Connect a signal generator to the input. Don't have a sig gen? Download a sig gen app for your phone. Set the sig gen output for 500Hz and 200mV RMS as measured with your DMM at the input jack. Now connect your DMM to the output jack. and adjust the volume and output knobs for 200mV RMS. Once you have it set to unity gain, plug your guitar in and readjust everything until you like the sound. :l2:
If you really need it to be set for unity gain, I think you may need another project. :wink:
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Thanks everyone. I'll give these methods a try.
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Am I correct that I have the VV plugged in and turned on so it has power?
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Doesn't have to be turned on to measure input, but it would be better to turn it on. Absolutely must be turned on to measure output.
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I was wondering if this oscilloscope that I saw on eBay would be worth the investment for a hobbyist like me, or do you think its too limited in what it could do: http://vi.raptor.ebaydesc.com/ws/eBayISAPI.dll?ViewItemDescV4&item=392828722788&category=104247&pm=1&ds=0&t=1591502285000&ver=0
Thanks.
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looks fine if our eyes are good with small screen
Max. Input Voltage: 50Vpk (100Vpp)
you'll need a 10:1 or 100:1 probe for PA stuff, but for normal signal path and frequency stuff looks ok
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I assume "PA" means Power Amp? I assume this scope would accept either of those 2 types of probes?
You can see I don't know anything about this!
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yep, power amp. 97% of the time I don't scope the plates any more, if it's good at the grid, bad at the speaker, there are just not enough parts to bust out a scope, meter, yes..
2 * MCX-clip Cables
scope probes use a BNC style connector, looks like that use's some type of sm? rf screw type connector so you'll have to "adapt". most scope jockey's have a bag full of gender benders, connection adapters and a dozen specialty cables
it is kinda a "hobby" in itself scoping signals, so jump in the deep end and learn to tread water :icon_biggrin:
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Most versions of that scope kit include a smc to bnc adapter cable. I still don't like the 50Vpk max input level. Fine for tinkering on low voltage ss or digital circuits but too fragile for tube stuff. One ah shit moment and the scope dies.
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I decided the screen was too small, and I purchased this model: https://www.amazon.com/Oscilloscope-Digital-Bandwidth-Functional-Portable/dp/B087TBFB3K/ref=sr_1_2?dchild=1&keywords=ADS1013D+oscilloscope&qid=1599670028&sr=8-2 on Amazon.
Looks like its more useful.
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bigger is better :icon_biggrin:
even if it comes with probes, pick up 1 quality 10X probe.
I very seldom use a scope for anything DC, that's what my fluke is for, that said, the signal might be riding on big DC so put a giant Note to self "ALWAYS HAVE IT SET FOR AC Coupling".
pretty soon you'll be showing all your friends cool waveforms :icon_biggrin:
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You're over my head already! Can you briefly explain the last sentence? I am familiar with the probe issue though. Thanks.
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pretty soon you'll be showing all your friends cool waveforms
You're over my head already! Can you briefly explain the last sentence? I am familiar with the probe issue though. Thanks.
He means now that you are entering the visual world of electrons, you can invite your friends over to show them what your guitar really looks like. Better yet, use the USB port to save your screens as images and post them on spacebook, or even this forum.
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Sorry, I understood that sentence, I actually meant the Paragraph's last sentence preceding that one. HaHa!
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Oh, you mean this one...
I very seldom use a scope for anything DC, that's what my fluke is for, that said, the signal might be riding on big DC so put a giant Note to self "ALWAYS HAVE IT SET FOR AC Coupling".
He means always set the input coupling to AC.
But I disagree with that statement. It's often necessary to view signal waveforms with dc coupling. Many times you need to measure the dc baseline on a signal. Can't do that if the scope input is set to AC coupling. Here's one example...
http://sluckeyamps.com/misc/Amp_Scrapbook.pdf
Look at page 9. You could not analyze that circuit if your scope was set to AC coupling. Or look at page 16. Need DC coupling for that also.
But if you need to check the amplitude of a 1v signal that's riding on a 300v dc level, you must use AC coupling because the signal and +dc level would be deflected so far off the top of the screen that you most likely will never find it.
My point is... know when it's appropriate to use ac or dc coupling. That will become more meaningful as you gain experience. I suspect one of the first things you'll want to do is look at the input and out waveforms of your unit and set for unity gain. In this case, either AC or DC coupling would be appropriate since the input and output waveforms both have a zero volt baseline. But if you try to trace the signal through the amp you'll find that usually grid signals are usually at zero volt baselines and plate signals will be at big positive DC baselines. In this case, AC coupling is a better choice.
Don't worry. You'll get it if you play with it enough. Then you can move on to proper triggering so you can actually see the phase reversals as you trace the signal through a device. :icon_biggrin:
I highly recommend a simple sine wave signal generator.
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+1
DC coupling is real handy, after you learn not to burn up a probe or a scope :icon_biggrin:
In my old life we had to measure AC riding on 1500 - 3500vdc, more than 1 newbie didn't take notes while the teachers demonstrated floating the scope, thankfully only scopes bit the dust. Engineers finally got around to designing voltage dividers for HighVolts :think1:
put some ice in a glass, your favorite single malt, watch some video of scope functions and operations. within a week you have your amp "spec'd" out, with amplitude, phase, frequency using a sine wave. then try looking at a complex guitar wave and give up :laugh:
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Thanks. I'm sure I'll have more questions, but will first try to understand the basics before hitting you guys with my questions.
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http://tubebooks.org/technical_books_online.htm#Test%20&%20Measurement%20(equipment,%20instructions...)
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This is a great resource. Thanks so much. Stephen
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Hi guys. I wanted to ask a favor of your thoughts and time. I got my tablet oscilloscope today, and am trying to figure out how to use it and what kind of simple tests I could do to start my learning process. It came with 2 probes that have 1X and 10X switches, its DC lithium battery supplied, and has a 400V protection circuit built in. So I'd like some guidance on some simple tests I can run just to see what it does and how to start using it. I have 2 things I'd like to check with it, but these may be more complicated than I should start with, but I'll tell you what I'd like to do.
First, I'd like to be able to balance the Output Level so that it is the same as the Input Level. It may not be useful for anything, but I'd like to see how to do that. I do have an iPad that can generate signals that I can connect to the VV through the earphone jack with a 1/4" phone jack.
Second, it has a low hum, maybe 60hz, that I'd like to figure out the cause. The VV Output runs into the Gretsch amp's input, and if I unplug the guitar input into the VV there's no difference so it seems like the hum doesn't arise from the input source, but if I vary the Output Level the loudness of the hum varies. I don't know if its something in the VV circuitry that I need to fix, like a ground somewhere, or if its because I've got 2 grounded amps, ie. the Gretsch and the VV, that are creating a ground loop or something. So I'm hoping that the scope could help me find the cause.
Any input from you is always appreciated. Thanks.
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I do have an iPad that can generate signals
start there;
create a 1khz sine wave with an amplitude of ~~ 100mVAC_RMS
read through the manual, find RMS vs peak to peak, I personally use RMS for everything audio, go so far as convert (math) tube data sheets "27Vac peak" to rms, then measure.
once you're happy with that, vary volts (amplitude) and frequency (period time) till you have a good handle on those 2.
If you can't get it to "sync" (signal keeps scrolling), read up on triggering, play with that til you're happy
then maybe you're ready to jack in and follow the signal through the amp
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On the VV unit, disconnect the green wire in the power cord from chassis. Does the hum go away?
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Sluckey, I haven't tried disconnecting the green wire yet because it's connection to the chassis is hard to get too. But, I saw that some people will use a 3 prong to 2 prong plug adapter to isolate the ground wire. So I did that, and plugged it into the wall receptacle, but no difference. So if this does the same thing as disconnecting the ground wire from the chassis, it must be something else.
I did note that I grounded the 4 big filter caps to a separate ground lug going to the chassis, rather than grounding them to the ground bus that most everything else is grounded to. I thought doing that would isolate them from the grounds of the rest of the circuit and avoid hum. Could that be the issue?
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Shooter-Thanks for the startup. I'll give it a try.
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I did note that I grounded the 4 big filter caps to a separate ground lug going to the chassis, rather than grounding them to the ground bus that most everything else is grounded to. I thought doing that would isolate them from the grounds of the rest of the circuit and avoid hum. Could that be the issue?
I doubt it, but temporarily connect the ground buss to the filter cap ground to see if it helps.
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I just realized that the E Node 1uf cap which is not with the others but over near the pre-amp section is Grounded on the Ground Bus, and not at the same location where the others are grounded, and of course its feed is coming from the others. Could this be it?
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I just realized that the E Node 1uf cap which is not with the others but over near the pre-amp section is Grounded on the Ground Bus, and not at the same location where the others are grounded, and of course its feed is coming from the others. Could this be it?
Doubt it but see my last post. Also, temporarily jumper a 20µF cap across that 1µF cap. Any better?
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The closest electrolytic cap I have is a 10uf 25V cap. Then I have a 100uf 16V. Would either of them work for this?
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PS nodes are typically high volts, so low volt caps only show their inerds if used :icon_biggrin:
don't have the schematic handy to verify though
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The closest electrolytic cap I have is a 10uf 25V cap. Then I have a 100uf 16V. Would either of them work for this?
no
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Yea, I didn't think they would work. I need 450V caps. I guess another purchase from Mouser or someone online. Its really frustrating that there isn't a electrical parts supplier within 100 miles of Charlottesville. Wow. So I'm in pause on this part of the test. Thanks.
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welcome to the new world, same as the old world except worse :icon_biggrin:
play with your scope, once you are confident that what you see, is what you expect, you can still trace out a signal with hum. that's lesson 2, .....by messing with scope settings you can see both the signal and hum, you can calculate the S/N (signal to noise). then you have a "baseline". that way when the hums gone you can re-measure, re-calc, celebrate that your S/N went way up :laugh:
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Sluckey, this morning I was going to start working on some of this stuff. The VV was unplugged. I haven't done anything to it yet. I turned on the Gretsch amp and let it warm up, and then when I was plugging the VV into the wall receptacle I started hearing the hum, but at a much lower volume level. I turned the VV on and it came up much louder to the level I normally hear. I turned it off, and then removed the plug from the receptacle. I noticed that just as the Ground pin on the plug was going into the receptacle, and before the Hot and Neutral pins entered the socket, that the hum would start. I then used the plug adapter that doesn't have the ground pin, and noticed that just as I was plugging it in, I could start to hear the hum at the same low level. Does this help your analysis? I guess its really quiet in the house this morning so I'm hearing stuff better than the other day. Thanks.
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I checked my wiring (I have photos) on the Ground lug and I have the green ground wire from the mains connected to the lug that is screwed to the chassis, and I also have the center tap from the transformer secondary (this transformer doesn't have a center tap for the filament wires) connected to the same lug--if that has any impact.
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this transformer doesn't have a center tap for the filament wires
In that case you need to make an artificial center tap using two 100Ω resistors. Connect one resistor between a filament wire and chassis. Do the same for the other filament wire.
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Yes, I did that with the resistors.
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I turned on the Gretsch amp and let it warm up, and then when I was plugging the VV into the wall receptacle I started hearing the hum,
so the Gretch is picking up the "extra" noise since the VV is off. ("I turned the VV on and it came up much louder to the level I normally hear.")
have you jacked them together by then or just powered up?
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They are jacked together with the Gretsch amp on, and the VV off and unplugged. When I start plugging in the VV into the receptacle, I can hear the hum starting on the Gretsch but at a very low volume. When I turn the VV on, and it warms up, then the hum is at the same frequency just much louder.
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Sluckey-attached is the initial drawing you gave me to get me started. I was wondering if I wired the connection at the input jack correctly. I ask in part because even when the VV is turned off and the signal is not going through the circuit, but the VV's output is plugged into the Gretsch amp, I get the hum when just the ground pin on the plug is inserted into the receptacle. So I was thinking the hum gets started early on.
I attached a lug with a bolt to the chassis right below the input jack as shown in the drawing. It obviously connects to ground through the chassis. And I also wired a jumper from the lug to the circuit board where all the components are leading to a ground, and then ran a separate jumper from the lug to the Ground Buss. Finally I ran the shielded input lead to the input jack "tip", not the "sleeve" as shown in the drawing, and connected the shield to the same lug as shown in your drawing. One side of the 1M R goes to the "tip" of the input jack, and the other side goes directly to the Ground Buss and not through the GND leg on the input jack. Finally the "sleeve" and the "GND" legs of the jack are jumpered and connected to the Ground Buss from the GND leg of the jack.
Assuming this is all correct, could the connection of the Ground Lug to the chassis where a lot of connections wind up, and then go on to another ground on the Ground Buss be the issue? Why did you use a lug to the chassis for those connections rather than just wiring them to the Buss? That lug is not isolated from the chassis is it? Thanks as always for your time and patience.
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One more point, my Ground Buss is bolted on one end to the chassis and is floating on the other end. Its stability is due to the gauge of the wire and the jumpers connecting to it. All of the ground legs of the pots, as well as the ground and sleeve of the Output Jack, connect to this Ground Buss.
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an experiment;
find a nice length of 12 gauge solid copper wire, a couple of small clamping "things" (small vise grips, hemostats, c-clamps). clamp one end of the copper wire to the VV chassis, clamp the other end to your Gretch (bare metal, not pained surface), repeat your plug in test (Using a cheater plug on the VV)
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Thanks. I'll give it a try.
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I wanted to also note that I have the same symptoms using my 5F1 Champ that's plugged into a different receptacle than the Gretsch amp, but they're probably on the same circuit. So its not just an issue with the Gretsch.
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Shooter-I did your test and it was a vast improvement. I used the cheater adapter also as you suggested. So I also tried just using the cheater adapter by itself after disconnecting the copper chassis ground wire, and it seemed to also clear up the signal. Maybe I had it inserted better on the plug than when I first tried it a couple days ago. If I remove the adapter as soon as the ground pin is inserted into the receptacle, and the other pins aren't inserted, and the VV turned off, I can start hearing the hum. With the adapter plugged in I don't hear the hum since there's no power amplifying the signal to the amp. If I turn the amp on, then there's some hum but substantially reduced. Its volume is controlled by the Output Level on th the VV.
So I also tested this with the copper wire connected to the 2 chassis, but without the cheater plug, and the hum was even better than when the cheater plug is used. Its practically gone!
So what does that tell us? Looks like a solution but obviously not something I can use! :sad2: :l2: :BangHead:
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I would use a braided ground strap to bond the two chassis together. Permanently bolt one end to your VV chassis. Install a stud bolt to the amp chassis. Use flat washers and a wing nut to secure the other end of the strap to the amp.
Amazon has a variety of "ground straps" available. Or build your own with a length of RG-59 or RG-6 cable. Just strip the outer jacket and remove the center conductor. Make it as long as you want.
https://www.amazon.com/Allstar-Performance-ALL76330-Copper-Ground/dp/B00F0CIO60/ref=rtpb_1/138-3958134-1216332?_encoding=UTF8&pd_rd_i=B00F0CILM2&pd_rd_r=5b891574-39de-43a5-b4a2-80194fb81558&pd_rd_w=ZokbT&pd_rd_wg=Ev0FG&pf_rd_p=49740592-2805-416d-896c-b825ad91c2cf&pf_rd_r=N85EH3ZW4V3Y0QDRENY6&refRID=N85EH3ZW4V3Y0QDRENY6&th=1
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Is this something that a balanced 1/4" cable with a balanced Output Jack would fix? Any idea what causes this? I'd like to avoid having to strap the 2 units together.
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Fender used a floating ground in the reissue reverb unit (see attached link). You would have to lift every ground connection in the unit from the chassis and float. This means, jacks pots, everything. The only thing connected to the chassis would be the green wire in the power cord. Then add CR5, CR6, and R23 connected ***BETWEEN*** your floating ground and chassis. This is probably a huge task. Makes the ground strap look like a good solution.
https://el34world.com/charts/Schematics/files/Fender/Fender_63_reverb_manual.pdf
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Is this something that a balanced 1/4" cable with a balanced Output Jack would fix? Any idea what causes this? I'd like to avoid having to strap the 2 units together.
Your VV has an unbalanced output and your amp has an unbalanced input. I don't see how a balanced cable will help.
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Yea, I figured the jacks would also have to be balanced.
Would an isolation transformer be a solution?
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possible, you still need to use isolated jacks in n out of the VV I believe.
What Steve said ^the "proper" fix is to "float" the VV, the alternative is to bond them both. I've done it twice for other ppl's equipment. I did Like Sluckey stated; used 400W speaker screw terminals, chassis mounted, and made up the braided jumper with soldered lugs. takes an extra minute to cable up, not a big deal
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Shooter-I was finally able to get a chance to try out my little oscilloscope as you suggested and was able to get the 1K signal showing just fine. I used the test signal from the scope and then I used the signal generator on my iPad to create a 1K signal and turned the output all the way up as you suggested. It worked fine.
So I guess I'm ready to try some simple stuff with the VV unit. One thing I'm not sure about is the AC vs. DC coupling and when to set it to which one. The scope can be set to 1X, 10X or 100X, and the probes have the 1X/10X switch. The manual gave some setups for various tests. One was to measure the AC voltage from a receptacle--which I have not done. The scope can handle up to 400 V, but it said I needed to set it to the 100X position and use a 100X probe-which I don't have. Seems like I could just set everything to 10X/AC. Is that correct? Thanks.
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1st, what's the manual say about max input volts (not 10x 100x), IIRC it was 40v :dontknow:
assume 40, then a probe set for 10X should "allow" you to measure 400v, there's a catch, some 1x/10x can ONLY measure 300v, so verify what you probes max V is
for signal path, keep it on AC coupling for now, once you get past the learning curve you can play with DC coupling.
You AC signal shouldn't be more than 100Vac so I'd feel comfortable saying a 10x probe, AC coupled will get you input to output just fine.
couple tips not to get "odd" readings, stay out of feedback circuits, TS, NFB.
probe grids on the "left" side of the grid R NOT at the grid, probe plates on the "left" side of the coupling caps, typically the plate R coupling cap junction.
I use both channels, I set CH1 at the input jack and leave it
I probe with ch2
that way you can "see" phase shifts, you can insure your input signal amplitude is ALWAYS constant (some tweaking may be required as you change frequencies)
before you power on, PRACTICE clipping the probe, do it many times, the last thing you want is a smoked probe-scope-amp error :icon_biggrin:
Make sure you're scope ground wire is secure, might need an extra gator clip to cover more distance, I always use chassis ground for everything
have fun
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Interesting development on the hum/noise issue. I wanted a shorter cable to connect the amp to the VV, and so I ordered a pair of Neutrik 1/4" plugs + 6' of Mogami guitar cabling. I had been using a name brand guitar cable that I had bought a few years ago, and it is 15' long. I made up the new cable, and not really thinking much about it connected up the amp and the VV, and WOW! the hum and noise are dramatically reduced--maybe by 75%. So maybe there is such a thing to using quality cable and connectors.
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Mogami cable has a substantial shield. Kinda like using a braided ground strap to bond the two chassis together.
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Shooter-When you say "probe grids on the "left" side of the grid R NOT at the grid, probe plates on the "left" side of the coupling caps, typically the plate R coupling cap junction", do you mean on the side of the resistor/cap opposite to the side that connects to the grid/plate, ie. before the signal goes through the cap/resistor?
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you can probe plates, you can even probe grids, but, your scope might "change" the signal some so I just probe the grid on the left side of the series grid resistor. that might simply be "each side of the coupling cap"
once you get a "feel" for what you expect and what you "see" and can reconcile them, you're set to probe anywhere, except PA tube plates - for now.
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Sorry, but when you say "left" do you mean the side of the resistor before the signal goes through the resistor and then to the grid?
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yep
scope>resistor>grid
for fun, once you do that, probe the grid (AC coupled), see IF there is a change on signal, that way you know for future reference
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I finally got a chance to get back to working with the OSC. I connected it up to the VV at the input jack and the output jack to see what balancing the input and output signals would look like. I got the output voltage set to the same as the input, and the results are shown in the attached pdf file. Looks pretty good? I turned on and off the vibrato and reverb and got reactions on the signal too. Any thoughts you'd like to share? Thanks.
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pop quiz;
1. what are the 2 signals phase relationship?
2. when you plug the output signal into your Amp, what effect does it have on the signal?
3. You like your scope don't you ? :icon_biggrin:
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I'll have to take this quiz tomorrow! The first question has got me stumped right now!
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Extra credit;
Channel 1 is ~ 100mV rms
channel 2 is ~ 300mV PP
WITHOUT using the scope, are the 2 signals ~ = ?
(calculators and computers are allowed :)
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I would say yes, they are about equal: 0.3535 x 300 = 106!
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I pointed that out because as a "general" rule you want all your measurements the same reference.
that way you got 2 apples instead of an apple and a banana
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Shooter, in answer to your reply 569 above, attached is an image pdf of the 2 signals overlaid. I don't know how to describe it except to say they seem to be like a helix, or something. I guess you would say they are in phase, but maybe they're actually 180 degrees out of phase. As to the sound when connected to the amp, its a high pitched whine, very solid, and oscillates when I turn on the vibrato. Signal seems very stable. Thoughts?
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they're actually 180 degrees out of phase
If they were in phase they would overlay so you couldn't tell one from the other.
phase is anything "shifted" from original, so a 10 degree phase shift might look "in-phase" until you overlay. your scope probably has a channel add, channel subtract feature. that comes in handy when you want to see really small differences.
what I was "looking for" is you scoping the output of the VV when you plugged it into your amp. If there is a "mis-match" ,(VV to amp), the VV's output signal will decrease some, maybe small mV, the greater the mis-match the more the signal gets loaded down.
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Ok, so I set it up and before plugging the cable from the VV output to the amp it read 108 VRMS on Channel 2 Output from VV. Then when I plugged it in to the amp, it read 103 VRMS, and didn't change when I turned on the power. So looks like a difference of 5 VRMS. Is that reasonable?
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Surely you mean millivolts? If so, that's good.
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Yes, mv. Sorry.
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without a calculator that "looks" like 5% drop in signal, I'd call that good, 20%, you might need a calculator to "fix" :icon_biggrin:
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In trying to learn more about using the OSC, can you all give me some pointers on things NOT to do so as to prevent "smokin'" the OSC or the VV? Thanks.
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I guess I'd like to learn how to trace a signal through the circuit and see what the signal looks like along the way, and how it reacts to the VIB or Reverb being turned on and off.
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know what you're "testing", so;
If i'm gonna probe a preamp plate, answer "all" the ?'s
how much volts
what kinda volts
do those values exceed my scope's capabilities
what do I "expect" to see
what "things" effect the outcome
have a trust and confidence in yourself, the equipment, know your limits
ask, I got more :icon_biggrin:
Oh, go through "your check-list" EVERY time you make a measurement, document well enough to decode tomorrow
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I wanted to trace the signal from input to output on the VV using my little oscilloscope to see how it changes as it goes through the various stages, and wondered if someone could show me on the Schematic that Sluckey did for me of my build, the path of the signal as it moves through the circuit. You know showing lines and arrows, or something like that. Just hand drawn and not elaborate unless you are so inclined. I'm attaching a copy of the schematic. Thanks.
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the signal path, in it's simple form is all the plates. set all the pots to 5, turn verb n trem off, inject a 50-100mV RMS signal. Note Steve already indicated the dry signal "past" the reverb.
repeat with volume at max
now repeat with trem on and note the changes.
again with reverb on dialed 5 on knobs, wet signal will be at the plates
the modulator is a complex, same with TS, when you "interact with scope", you alter the results, kinda like modern day voting :icon_biggrin:
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Shooter, thanks. What is TS? What really confuses me is figuring out the path of the signal into and out of the Vibrato Oscillator/Driver section. Can you describe that path for me? Also, do I set the oscilloscope to AC or DC? I assume AC, but you know what they say about assuming anything!
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TS = tone stack
AC coupled, I haven’t got a chance to color the pdf.
Start small, T B n Vol at 5 ch1 on input jack, ch 2 trace probe
Inject signal, measure V1A plate, then V1B plate.
Now set Vol to 10
Repeat
Now set vol back to 5, set treble to 10
Repeat
Set treble to 5 and Bass to 10
Repeat
Move probe to the “white ” point between V5 and V6
Repeat above knob settings
Now turn on trem, all knobs 5 repeat again.
screen shot for each condition, note the "conditions"
set up a video loop of the conditions and "grasp" why things changed
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What really confuses me is figuring out the path of the signal into and out of the Vibrato Oscillator/Driver section.
The guitar signal never enters the osc/drv block. The first half of the 12DW7 is an oscillator, aka a LFO (low frequency oscillator) or signal generator. It generates a low frequency sine wave that can be viewed on the scope just like any other sine wave. But the frequency is very slow, about 3Hz to 10Hz, so you must slow down the time base speed of your scope, or just press an auto button if you have one. A very convenient place to view this sine wave signal is at the top of the INT pot. This will be a strong signal, but it's slow. The speed pot will change the frequency of this signal. You can use ac or dc coupling because there is no dc voltage present at this point.
The LFO signal from the INT pot is applied to the second half of the 12DW7, which is a standard cathodyne phase inverter, aka a phase splitter. The phase splitter produces an output at the plate and also at the cathode. These two signals will be exactly the same as the signal from the INT pot but they will be 180° out of phase with each other. You can view these signals at pins 1 and 3. Use AC coupling since these signals will be riding on a healthy DC voltage. These two signals exit the osc/drv block and head up to the modulator block where they do their magic to the guitar signal.
That's about all there is to the osc/drv block. Once again, the guitar signal never enters the osc/drv block.
If you will measure all the tube pin voltages (don't care about filament pins), power supply nodes A, B, C, D, and E, and line voltage, I'll put those on the schematic for you. They can come in handy if you ever find yourself troubleshooting a broken unit. I also like to include the LFO signal at the top of INT pot. I like to set the speed for 5Hz and measure the peak to peak amplitude. This can be handy when troubleshooting a weak or dead oscillator.
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Thanks to both Shooter and Sluckey- Its no wonder I couldn't figure out how the signal goes through the Oscillator--it doesn't! I'll take some voltage readings and send them up to you Sluckey. Thanks again.
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Sluckey, do I need to have a signal going into the amp just to test the voltages?
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no
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Here are the voltage readings. Thanks. Stephen
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Can you measure this one also?
...I also like to include the LFO signal at the top of INT pot. I like to set the speed for 5Hz and use a scope to measure the peak to peak amplitude. This can be handy when troubleshooting a weak or dead oscillator.
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Could you tell me how to hook up my scope's connections so I can do that? I'm just trying to learn on this device.
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Connect a probe to the top lug (not the grounded lug) of the INT pot. Connect the probe's ground clip to chassis. That's all.
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Ok, so I hooked it up, and ran autoset, and then adjusted the Vibrato Intensity pot until I got a reading of 5HZ, and the VPP is reading 42.5V on the screen. Does this sound correct or reasonable?
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Ok, so I hooked it up, and ran autoset, and then adjusted the Vibrato Intensity pot until I got a reading of 5HZ, and the VPP is reading 42.5V on the screen. Does this sound correct or reasonable?
Looks good but surely you adjusted the speed pot for a reading of 5Hz? Are you sure the 42.5V is peak to peak?
Also, what is the frequency with the speed pot set max CCW? and max CW?
You may notice the voltage reading changes as you turn the speed pot. That's normal. It's also why I specified to measure the voltage with the speed set to 5Hz.
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I used the Speed Pot to set it to 5HZ. The Vibrato Intensity Pot affects the VPP reading depending upon how low or high the pot is set. Where should it be set to get the VPP for this test?
Speed Pot Max is 7HZ
Speed Pot Min is 4HZ
The VPP goes from around 20V at a minimum setting of the Intensity Pot to a high of about 78V at its maximum setting.
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Actually the VPP has a much wider Voltage range that I indicated when the Vib Intensity pot is adjusted from minimum to max.
I did make a change in the Intensity pot type. I changed it from an audio to linear taper. It gives me better control over the intensity.
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All good info. But I'm trying to get a set of numbers to put on the schematic that you can refer to later on. So, set the INT to zero and adjust the speed pot for 5Hz. Now measure the peak to peak LFO signal at the top of the INT pot. What have you? I'll put this number on the schematic with a note of how the pots were set.
Here's another little scope exercise for you... While observing the LFO sine wave with the pots set as above, adjust the time setting of your scope to show two (or more) complete cycles. Now save (or print) the screen to an image file (usually jpg or png format). Attach the file to your next message. I want to see it and may even put it on the schematic.
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Ok, its at 5HZ and reading 2.78 VPP with a Vrms of 882mv. Attached is an image of the scope screen in pdf format.
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I don't understand. Now you have less than 3Vpp. Earlier you had 42Vpp, then a range of 20 to 78vpp. What are you doing wrong?
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Well before the Intensity Pot was turned up about mid-way, so you said to turn it down to 0, so I turned it down as low as I could go and still get a 5HZ signal, before it got to a flat line. So the VPP varies with the setting of the Vibrato Intensity.
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Not if you have the scope connected to the TOP lug of the pot as I requested.
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I've got it on the middle lug. Is that not the TOP lug?
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No. The middle lug is the middle lug. The top lug is the top lug. LOOK AT THE SCHEMATIC. It'll make sense then.
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I moved it to the input lug, set it to 5HZ with Vib. Speed pot, and it reads 224Vpp and Vrms of 71.6 V.
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Here's an image of the Sine Wave.
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I moved it to the input lug, set it to 5HZ with Vib. Speed pot, and it reads 224Vpp and Vrms of 71.6 V.
That's what I'm talkin' about! :thumbsup:
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Here's the updated schematic with voltages.
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Sluckey-This is great. Thanks so much for all of your help. Best. Stephen
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Having the voltages on the schematic will be very useful if you ever need to troubleshoot the unit if it fails. And having a visual scope pic of the vibrato signal helps to understand exactly what is going on in the oscillator circuit.
FYI, that oscillator is called a phase shift oscillator, sometimes called RC phase shift oscillator. Lots of google theory info if you want to read about how it actually works.
The Gretsch 6163 amp even uses this same oscillator (higher frequency though) as a built-in "tuner" signal.
https://el34world.com/charts/Schematics/files/Gretsch/Gretsch_6163.pdf
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Does my scope image look good, ie. the way its supposed to be when working properly? Thanks for the Gretsch schematic. I have the Gretsch 6165 Supro Amp which I think is pretty much the same as the 6163. Its a really nice amp. I've had it since new in 1966, but the actual number of On Time/Playing hours is pretty small. I got it in high school, and then went off to college etc., so my playing days were numbered. Its nice to be able to use it, and still with the same tubes.
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Scope looks good. More than adequate for this stuff. One slight discrepancy... Display graticules showed frequency to be 5Hz and 5.2Hz on the two pics using the old fart analog method of counting graticules, multiplying times time/division, then getting reciprocal . Your FREQ numeric readout showed 5Hz on one pic and 4Hz on the other. Maybe the counter can only resolve to one Hz? Not a big deal unless you're gonna fly this amp to the moon. :icon_biggrin:
There are way more features on that scope than you'll ever find a need for working on a tube amp. Kinda like using a scientific calculator to balance your check book. :laugh:
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I tried my scope today to see what the signal at the Output jack looks like when both the Vibrato and Reverb are Off, and then when the Vibrato is Off and the Reverb is On. Attached the 2 files. I don't know if this looks normal or not, but thought I would ask for your comments.
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do you have 2 probes?
If so;
use ch 1 connect to input jack and leave it
use ch 2 to "move along the path"
the "hitch" shouldn't be there with both off, (i think)
what were your tone n vol set at?
when doing "spec", you want to be able to repeat those conditions EVERY time you measure, otherwise you add variables that can n will mess up your "spec"
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Shooter--Attached is a scope image showing both channels. Ch.1 is at the input jack where the 1KHZ tone is coming in, and Ch.2 is at the output jack. I have a guitar cable plugged into the Output jack, but the other end of the cable is not plugged into anything. Both are set to AC and 1x on the probes. Both are showing 200mV/div. Both VIb and Rev. are off. All pots are at Noon position. Both Vppp are around 300mv, and both Vrms are 99mv. I did this same check a month or so ago and they were both smooth. Any idea where to probe to find the source of the hitch?
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If I lower the Input Volume Pot from Noon position where it gets me 99-100 Vrms, to about 8 o'clock position where it reads 50Vrms, then it smooths out, but of course the amplitude or heigth of the signal is much shorter.
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find the scope setting were you read volts AC RMS, that should be a "standard" when measuring signals.
so the input should be 50-100mV rms
leave that as your "baseline"
now measure the output, IF it's "clean" (all knobs @ 5..reb, trem OFF) then that will be your "spec". note all the settings on your schematic. then 12yrs from now you can "see" where things went wonky.
all these are arbitrary settings, it's just a means so you can compare apples to apples in the future
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Thanks. When you say "5", do you mean "5 o'clock" position (basically the pot is turned all the way up), or 50%, or what exactly?
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half way
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Sluckey-I've been looking at some schematics of the M-9 and the M-10 models, and in the oscillation section they have a .02uf cap coming off plate 6 of the 12DW7 tube which then connects to the .068uf cap that then connects to the top of the 1M Vibrato Intensity pot. Looks like the m-10A changed that to delete the .02 cap. Do you know why that was done, and what the effect would be on the pot and circuit?
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The bean counters said you don't really need that cap so it was removed. Savings = $0.25. Pure profit!
That cap was a smoothing cap to make the sine wave look smoother. Why don't you temporarily put a .02 (or .05) cap from plate to ground and look at the top side of the INT pot with your scope. Does the cap make the waveform look smoother, more like a sinewave? Post a pic for all to see. BTW, it's fine to post an image file rather than convert to pdf. Easier/quicker to view.
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Will do. I noticed on your drawing that the M2 used 2 .02uf caps rather than a .02 and a .068. Sometimes my image files were too big to post so I converted to PDF.
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...my image files were too big to post so I converted to PDF.
Irfanview
http://www.irfanview.com/
https://el34world.com/Forum/index.php?topic=10974.msg100982#msg100982
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I attached a .02uf cap at the input of the .068uf cap that it's other lead goes to the Top side of the Vib Int pot, and connected the other end of the .02 cap to the BUSS gnd. I then injected a 1KHZ signal and probed it at the TOP side of the Vib Int pot. Attached is that image. They look pretty similar to me. For some reason though it makes a horrible buzzing sound after adding that cap. So that's definitely coming off. Any ideas why? Sorry, but it was a .bmp image that this website doesn't accept so I had to change it to a pdf.
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Don't know why.
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Any reason it should be grounded somewhere other than the Buss bar ground where the Vib. Int. Pot is also grounded?
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Well I moved the Ground side of the cap off of the Buss bar and onto the ground bar where the filter caps are grounded, and the hiss/noise cleared up! Can't imagine why! Does it matter on which side of the .068 cap I connect the .02 cap, ie. on the side where the Plate signal comes in or on the other side of the cap?
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Just follow the schematic.
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....it was a .bmp image that this website doesn't accept so I had to change it to a pdf.
https://el34world.com/Forum/index.php?topic=25746.msg293111#msg293111
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Well adding that .02uf cap to the front end of the .068 cap and grounding the other end of it to the filter cap ground buss really solved everything. No more of the mild hum, buzz or oscillation of any kind when the reverb is turned on with the vibrato. I had been getting some background oscillation I think from the LFO section that was bleeding through the reverb circuit when the reverb was on. Now its as quiet as when the effects are on as when it bypasses them.
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Well guys, I'm getting restless and need another project. Any ideas/suggestions you have would be greatly appreciated. Happy Holidays to All. Best. Stephen
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This simple project is my favorite...
http://sluckeyamps.com/dual_lite/dual_lite.htm
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Looks like a possibility to keep me busy for awhile if I decide to pursue it. What is it about this project that makes it a favorite? So does this "amp" give you the "sounds" of a Vox and a Marshall that you can use to expand your playing style? Since I have my Vibrato/Reverb project as an effects unit, it could be plugged into this to give these 2 amps the benefit of vibrato and reverb. I wonder if I could change this project to have a "floating ground" (I think that's what someone in this forum called it) system like the ReVibe circuit uses in order to eliminate any hum caused by ground loops? Thoughts?
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What is it about this project that makes it a favorite?
Simple, small, great sound.
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this is my simple;
the schematic posted "will be" the 4th iteration.
should yield ~ 8-10W clean and ~ 17W full on.
it's a tinker'rs amp, I typically add 6-12 extra turrets for changes, takes pedals well.
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Thanks Shooter. I'll check it out! How do you think it will do with my VibroVerb build? Any ground loops issues since there would be 2 devices, ie. the amp and the VibroVerb, running off of separate power supplies and grounds?
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not sure, only had pedals with batteries in front. SE amps are hard to keep/get hum low as is.
you did a basic "mechanical" ground earlier, I wouldn't be surprised if a grounding strap was needed
maybe a differential line out on the VIBVEB :dontknow:
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What are "SE" amps? How would you do a different line out?
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SE = single ended
PP = pushpull
SE amps operate in class A, A1
PP can operate there, but they can get to class AB2
Differential, not different
look up audio differential line drivers.
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Sluckey, Shooter et al, I just started a new topic and hoped maybe you can help: https://el34world.com/Forum/index.php?topic=26944.msg295588#msg295588
Thanks. Stephen
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Sluckey/Shooter-I've noticed that my VibroVerb has some mild "fuzzy" sound that increases only with the Volume or the Output Level pot. I don't know if you'd call it gain/breakup or what. Its not affected by any other control. Its probably always been there, but I have just recently started to focus on it. I was wondering if it could be that the Input resistor is a 4.7M resistor and not a 1M as is commonly used? Why would Magnatone use such a large resistor here? I haven't put my scope on it yet, but was looking for some insight. Thanks. Stephen
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not understanding
you say your vibroverb, but then you insert the magnatone
so without a schematic I'm going with the 4.7M as "grid biased" vs the 1M "typical" being cathode biased
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If you suspect the 4.7M just change it. Much quicker than typing this confusing message.
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Sorry for creating confusing. I've referred to this build that you guys helped me with last year as a "VibroVerb", since I was wanting to build a ReVibe type unit but it was based on Sluckey's M10A, ie. Magnatone, schematic that he modded.
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Here's my issue. My Magnatone 10-A Mod (which I've referenced at times as a VibroVerb ((Not realizing that Fender also used that name)) ) that I built based on Sluckey's changes as shown on the attached schematic of the finished product, works great except that the Treble starts to get "fizz" in the sound if its turned higher than about 9:00 p.m., and if I want more output from this unit in order to be at a similar level to the amplifier its going through so that I don't have to increase the amp's volume, I get what I'll call "breakup" starting at the Noon position on the Volume level pot. I can increase or decrease the output of the unit by increasing either the Volume Level or the Output Level, and the effect is the same. So I'd like to be able to get more Treble without the "fizz", and more volume to match the volume of the amp, without breakup. I have scope images if interested.
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What amp is this plugged into? Do you have an amp with a power input jack such that you could connect this unit directly into the other amp's power amp?
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Yes, I'm using it with the build I just completed with your Magnatone Twilighter Mod. I added an aux. power source so I could plug directly into the amp. I've also used it with by 5F1 and my Gretsch 6165, neither of which have aux. power inputs.
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So what does it sound like when plugged directly into the power amp?
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Just as I described. Also some minor hum that increases a little when reverb is active.
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I want you to connect V1 pin 6 directly to V5 pin 2. This requires you to remove the .047 cap and the wire between V1-1 and V5-2 indicated in the attached schematic.
This will totally bypass the volume and tone controls. Evaluate the sound and report back.
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Ok, so NO pots are functioning for Volume, Treble or Bass Pots.
Output Level pot controls volume.
Vibrato not functioning.
Reverb working as normal.
Sound seems unaffected. When scope is connected, see image attached, shows "dirty" signal, but the "dirt" appears the same regardless of the Output Level setting. The amplitude,ie. the VRMS and the VPP, of the signal increases/decreases with changes to Output Level pot, but the shape of the "dirt" at the bottom remains the same regardless of the Output Level setting.
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Where is channel 1 connected? Where is channel 2 connected? If channel 1 is connected to the input jack, then turn the signal level down to 100mVPP.
The simple changes I asked you to do have should not have interferred with the vibrato working.
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Sorry, I had only the input signal going into the input jack and no probe was connected to #1, so I don't know why there was an image. Anyway, I ran the scope again and the image is attached from Probe #2 and set for VRMS 100mv. Only Probe 2 is connected.
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Ok, I can get the Vibrato to work, but the Intensity has to be at 99% of the way Clockwise, ie. turned up. Back if off just a hair, and its not audible. Works fine with the circuit wired as before.
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I'm out of ideas. Good luck.
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Thanks for your help Sluckey.
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Where is channel 1 connected? Where is channel 2 connected? If channel 1 is connected to the input jack, then turn the signal level down to 100mVPP.
Sorry, I had only the input signal going into the input jack and no probe was connected to #1, so I don't know why there was an image. Anyway, I ran the scope again and the image is attached from Probe #2 and set for VRMS 100mv. Only Probe 2 is connected.
Where did you connect probe #2?
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Probe 2 is connected at the Output Jack. Probe 1 was not connected in this last photo. The shape of the signal as shown in the last image posted, stays the same regardless of the Output Level setting. Does the shape of the signal tell you anything about the cause? I'm a real novice, particularly with scope stuff.
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How would increasing the size of the 470pf cap going into the Treble pot affect the symptoms I've tried to describe?
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I don't know what the scope pic means other than it's a little distorted on the bottom 1/2 of the sine wave. (I have no experience with scopes.)
I think you have to verify that the test tone is clean 1st. So put your probe on the input jack and run your test tone in to check that 1st. If the tone signal is clean then.....
Then you have to 'divide and conquer'.
You have to find exactly where that signal is getting distorted. That FX unit is 4 separate stages, 5 if you include the power supply (PSU). You put your probe on the output and that doesn't tell you where it's distorting.
You want to see if the 1st section/block, the preamp V1-A/V1-B, is clean. I think Sluckey had you take the tone controls and volume control out to eliminate them as the problem. So do that but put your probe on the plate of V1-A. If you clip in a small cap, 0.02, 0.047, what ever you have handy, to V1-A's plate that will block the dcv and you can read the ac sine wave.
If the wave is clean, then hook up the tone/volume controls again. Now with the probe in the same place, far end of coupling cap hooked to V1-A's plate, see if the sine wave is still clean. If clean, it's not the preamp V1-A/V1-B section.
Stay focused on the sine wave 1st. If it's really distorting, and not the signal generator, if you can find where it's distorting, which section, then you can find out why it's distorting. Then your treble fizz might go away.
If the preamp sine wave looks clean, then reconnect the 1st section/preamp to the 2nd section/vibrato modulator V5 and the vibrato oscillator/driver V4. Disconnect the 0.0022 cap from pin 2 of V6. Hook up your probe to the open end of that cap. See if the sine wave is clean there.
Stay focused, don't worry about the 470pF treble cap, that's not the problem, unless the cap got cooked when you put it in.
Output volume can be worked on later.
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Do you have a layout drawing?
Long thread, or I'd look for it. :w2:
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Yes I have a layout I can post tomorrow.
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The input signal is clean. No issue with that. With Probe 2 on output jack, the signal is clean until the Treble pot is turned past 9:00. Then you start seeing the distortion on the bottom of the signal. Changing Volume pot or Output level pot doesn’t affect it. It’s solely controlled by the Treble pot. If you increase Treble, the Amplitude and the VPP/VRMS increase but the signal still has the same shape at the bottom. So it seems to me that the source of the problem is in that part of the circuit. That’s why I was thinking that changing the cap may be a solution. I know some will say “Change the cap and see what happens “. Yes I can do that, but I figure that the less I solder and unsolder a joint the better. Why take something apart if there’s no reason to. Maybe stupid, but that’s my thinking. Hope this makes sense. I’ll try some more probes on the circuit tomorrow and post my findings.
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The input signal is clean. No issue with that.
How do you know that?
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With Probe 2 on output jack, the signal is clean until the Treble pot is turned past 9:00. Then you start seeing the distortion on the bottom of the signal. Changing Volume pot or Output level pot doesn’t affect it. It’s solely controlled by the Treble pot. If you increase Treble, the Amplitude and the VPP/VRMS increase but the signal still has the same shape at the bottom.
The tone stack in your build with treb/bass set to 12:00 is flat. So treb set to 9:00 treble is still cut not boosted. Adding treble causes the problem, seems to be parasitic, or that cap is bad, or the solder connection is bad.
So it seems to me that the source of the problem is in that part of the circuit. That’s why I was thinking that changing the cap may be a solution. I know some will say “Change the cap and see what happens “. Yes I can do that, but I figure that the less I solder and unsolder a joint the better.
Why take something apart if there’s no reason to.
There is a reason according to your explanation.
Change the cap.
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As to the input signal, I’ve posted images of it on probe 1, yellow, connected at the V-1 pin from the input jack, along with probe 2, blue, at the output jack showing the issue. I think the file is named 14.pdf. As a reminder, changing the Bass pot has no effect on the output signal. So in replacing the cap, do you have a thought on value? Thanks.
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See post 652 for the file image 14.pdf.
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So in replacing the cap, do you have a thought on value?
Same value.
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Here's the Layout.
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Thank you, I found it yesterday.
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Well, I used Probe 1 to check the signal coming from the Input test tone, and probed it at V-1 Pins 1, 2 and 6, and V-5 Pins 2 and 6, both sides of the .047uf cap and the 470pf cap, and at terminals 1 and 2 on the 1M Treble pot (I think its a linear and not an audio pot), and other than changes in the VRMS/VPP the signal stayed the same and clean if the Treble Pot was around 9:00 or less. I could get good amplitude at the Output probe, and a clean signal, even if I increased the Volume or Output Level pots, as long as the Treble pot stayed at that setting. So maybe its something with the pot. But I guess since I feel like I've found where the clean sound is located, and I can get the Output level, then why should I worry with the amount of treble in the signal. Interesting though that the Bass pot doesn't have the issue. Maybe its time for me to just let it go.
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Your not being clear. Does the signal get distorted when you turn up the treble pot past 9:00 at pin 6 of V1-B, the input triode? If it stays clean, then it's happening after the tone stack/volume pot.
I thought you were going to change that 470pF treble cap? When you change that cap, use a heat sink on the leads when you solder them. There have been many builds here that it ended up being a small cap causing problems like yours. You spent all this time on this build and you wont change a cap?
Forget about the output. If you get the signal cleaned up where it's coming from then the output will be fine. The output volume can be increased be changing the voltage divider at the output and maybe by adding a bypass K cap on V1-A.
That series 1M R in the voltage divider will kill off highs. The 1st thing to go with a high value series R is the hi end, that's why Fender used a 10pF cap across the 1M R in the BF reverb amps, to restore the highs. Hi gain amps use them too across the series R in the voltage dividers. Very common. You could try bypassing it with a small cap, start with 10pF. But that might make your fizz problem worse. So you have to find/fix that 1st.
This sounds like;
1. That 470pF cap is bad or a bad solder joint.
2. Parasitic problem, only happens when you turn up the treble. Grounding/lead dress.
3. Treble pot could be bad, or bad solder joint.
4. Grounding problem, causing symptoms like/close to #2. There's a few things I'd try if changing that cap and maybe the pot didn't fix it.
If those things don't fix it there is a band aide trick you can try, that should fix it.
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Thanks for the encouragement. I'll do as you suggest and get back later today or tomorrow.
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I think you can fix it. :icon_biggrin:
I think it's just fine tuning it a little now.
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You have tried different tubes for V1?
Sometimes a tube will sound fizzy.
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Set both scope channels to measure VPP, not VRMS.
Connect your test tone signal to the input jack. Connect scope CH1 probe to the input jack also and set CH1 for AC 1X 50mV/div. Adjust the level of the test tone to be 100mVPP (***NOT 100mVRMS***) as seen on CH1 display. You should have a clean sine wave that is two vertical divisions tall. Don't change any of this throughout your testing.
NOTE! You may have to change the mV/div vertical sensitivity to keep the sine wave on the display while making the following checks with CH2 probe.
Now set CH2 for AC 1X 200mV/div and connect the probe to V1 pin 6. Save the scope image to a jpg or png file with the name V1-6.jpg or V1-6.png. ***PLEASE, NO MORE PDF IMAGES!***
Next, move the scope probe to V1 pin 2. Adjust the BASS, TREBLE, and VOLUME to mid position. While monitoring V1 pin 2, adjust the TREBLE pot to see if the distortion appears. Save the scope image to a jpg or png file with the name V1-2.jpg or V1-2.png. ***PLEASE, NO MORE PDF IMAGES!***
Finally, move scope probe to V1 pin 1. While monitoring V1 pin 1, adjust the TREBLE pot to see if the distortion appears. Save the scope image to a jpg or png file with the name V1-1.jpg or V1-1.png. ***PLEASE, NO MORE PDF IMAGES!***
Post your findings with these three image files attached.
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Here are the images. My scope just does auto-setting for the images.
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Here are the images. My scope just does auto-setting for the images.
jpg is just fine. Much better and easier/faster to view than your converted pdf.
No sign of that kinked/crooked waveform on the bottom of the signal. In fact, V1 pin 2 looks exactly like the input signal. So I'd quit suspecting anything before V1-2. That includes the 470pf cap. V1 pin 1 is a little slanted. May be due to loading from V5. How about pulling V5 tube and put CH2 probe back on V1 pin 1. Save the display pic as V1-1b.jpg.
Next, put V5 back in and move CH2 probe to the output jack. Adjust the output level for 100mVPP. Save the display pic as output.jpg.
Report your findings and attach these two pics to your message.
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Thanks. Will do, but the cocktail hour has arrived, and so my Manhattan is awaiting me. I'll report back in the morning. Thanks again for everyone's time.
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Question about your layout. In the attached pic I have circled three groups of turrets. Is the center turret in each group connected to the left and right turrets?
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The dotted lines are for jumpers going under the board. The only instance where there is a connection is in the lower group where the 47K resistor is jumpered to the .1uf cap on the right. That cap is also jumpered to the other .1uf cap on the left under the board.
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Actually its the .1uf cap on the left, jumpered to the 47K resistor, which is then jumped to the other .1uf on the right.
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I did switch the 12ax7 from V-1 to V-7 positions as Wallabe suggested, in case it might be a tube issue. Then I did as Sluckey requested. The Input on Probe 1 is set at about 100 mvPP, the Volume, Treble and Bass pots are all midway at Noon position, V-5 tube is removed, and then Probe 2 is connected on V1-1 and the image is attached. Then I installed the tube, and moved Probe 2 to the output jack and adjusted Output Level pot until it read about 100mvPP and the image is attached.
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So, the output looks fine when the input signal is 100mVPP. But when the input signal is 431mVPP the output gets the kink in the negative portion of the waveform.
431mVPP is much hotter than a typical guitar and is just overdriving the revibe. 100mVPP is much closer to the output of a typical guitar and is the level you should set your signal generator output whether you're connecting to the input of your revibe or any guitar amplifier.
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So what I understand that you're saying is that I just need to tone down the output of the unit, and find some treble/bass settings that I like the sound of and then adjust the volume/output pot levels to keep it to an output level at the output jack of about 100mVPP.
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I guess part of my problem was that I thought I had read that I should use a setting of 150 VRMS for the typical output of a guitar, and maybe that should have been 150 VPP. The VRMS reading of 150 results in a much higher VPP figure. So, am I correct that I should be using an input Test Tone Signal of 100-150 VPP when scoping any guitar amp or effects unit like this one?
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No. What I was saying is don't overdrive the input of the revibe because doing so will kink the output.
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Yes, I understand what you're saying.
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if you have a 1/4" jack laying around;
plug your guitar into it, clip a scope probe to the 2 tabs on the jack and play.
what I've found;
hot pickups played real hard come in ~~~~~~ 200mV rms
that's when you're going for the Jimmi in you :icon_biggrin:
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No. What I was saying is don't overdrive the input of the revibe because doing so will kink the output.
So what's the bottom line here?
There's nothing wrong with the build? He was getting a false scope reading because he was inputting to much signal and/or setting the scope for vrms, not vpp and/or turning up the input gain/volume too much? :think1:
So if that's correct ^^^^, then if he doesn't turn up the input volume too much, the hi end fizz won't be there?
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Nothing has changed, except he should know the proper signal level to inject into an amp.
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I guess some confusion for me now exists because Sluckey says use an input tone signal of 100mVPP and Shooter says the output of a guitar is around 200mVRMS. And they each result in significantly different strengths for an input.
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I guess some confusion for me now exists because Sluckey says use an input tone signal of 100mVPP and Shooter says the output of a guitar is around 200mVRMS. And they each result in significantly different strengths for an input.
Sigh!
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^^^^^
I said;
that is the MAX
what I was INFERING;
measure your own guitar, find out WHAT "normal IS" for your equipment
Also;
what has already been pointed out
volts RMS
and
volts PP
are different, pick one, DON'T mix them, they cause extreme heartburn when mixed :icon_biggrin:
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Now that makes sense.
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hot pickups played real hard come in ~~~~~~ 200mV rms
You probably don't have high output pickups and don't play real hard.
Adjust the level of the test tone to be 100mVPP (***NOT 100mVRMS***) as seen on CH1 display.[/u] You should have a clean sine wave that is two vertical divisions tall. Don't change any of this throughout your testing.
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In the novels I read;
a lawyer will not ask a question they don't already know the answer to
As a tech, i don't probe willy nilly without knowing "what to expect"
sometimes, both professionals are surprised with "the reply", that's where the fun begins :icon_biggrin:
EDIT:
I did most of the testing with a musician, playing a early 60's Les Paul, stock.
I found spikes as high as 2+ volts but the mean average over time was 200 - 250.
once I had "that number" I "tuned" amps around that value, so ya, not a big sample set
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As a retired attorney who did some litigation, Shooter is right unless you really want to know “If the glove fits, or if you must acquit.” I’ll get some readings on my Strat and my Gretsch Country Gentleman, and I’ll let you know what I find.
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So the Gretsch with humbucker style pickups looks like its between 100-125mVPP when both are active and in the neutral tone position, and the Strat using the Middle single coil pickup is lower, maybe in the 90-110mVPP range. Its not much difference when I use just the bridge or the neck pickup. Can get a little bit higher on both numbers when strum really hard.
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How 'bout that! Maybe you can explain to shooter how to do that. :icon_biggrin:
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pretty sure reply 690 indicated "how Shooter would measure....."
with follow-up clarification later in the posts...
I could use some help with what others have measured for MAX outputs from their pickups, well not me, i'm an UAS aviator now, I like the instant gratification, tube amps take way to long :icon_biggrin:
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Well my numbers were jumping all around, or course, but I figured those numbers I gave were probably in the average range. I did get some numbers over 150 mVPP, but that was hard strumming. Anyway, I'll check it out later and see if the "fizz" I was complaining of is gone-----or if it still lingers.
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Your scope may be capable of capturing the minimum, maximum, and average voltages.
As for fizz, use a 100pF cap and a couple gator clip test leads to connect the cap between chassis and various points in the signal path. I suggest these points and in this order... V1-6, V1-1, V6-1, V7-1, and V7-6. If you find a point that reduces the fizz, then permanently install a 100pF at that point. Then continue testing with the remaining points. Play guitar for a while to be sure you didn't lose too much high frequency sparkle.
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Well isn't that a coincidence .. got my Estey T-35 back yesterday cause the guy hit some hard times.. and found this thread. yeah varistors and this vibrato / trem sounds awesome..
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Well even with the suggested settings we've discussed, I still get the breakup in Treble tone when the pot is advanced past 9:00. So to keep it clean, I'll just leave it there. I was thinking maybe the Pot is too big. I have a 1M audio taper installed. Would a smaller size be better, or should I just leave my obsession and go on with other things?
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1M is the correct pot value. Verify that your actual amp wiring agrees with the schematic.
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I was thinking of a 250K Linear only because the Twilighter Mod that you helped me with and that I just finished uses that one. Interesting that that schematic shows a 250K Linear for Treble Pot, but a 250K Audio for the Bass. The Volume pot is also Audio taper.
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I was thinking of a 250K Linear only because the Twilighter Mod that you helped me with and that I just finished uses that one. Interesting that that schematic shows a 250K Linear for Treble Pot, but a 250K Audio for the Bass. The Volume pot is also Audio taper.
FORGET ABOUT THE TWILIGHTER! It uses a Fender tonestack that is not even similar to the M10 James tonestack.
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I played a new Magnatone a few years back at Chicago Music Exchange, huge guitar store, ~1000 guitars there.
It was a stereo vibrato Maggie, 2 x 6V6 left, 2 x 6V6 right, 1 x 12" speaker for each left/right channel. But its only a single phase shift stage on each channel.
I LOVED it!!!!!! LOVED IT, LOVED IT, LOVED IT!!!!
Did I say I LOVED it? :laugh:
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I"ve never heard one in person, only on the internet. But the sound is great. The M-10A mod I did last year with 4 NOS Varistors creates the fantastic vibrato that I really love. Its nice to have the Vibrato as well as the Magnatone Tremolo available to me. I think those sounds are really unique.
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When I 1st plugged in I set the vibrato switch for mono, it was pretty underwhelming. I thought this doesn't sound anything like Lonnie Mack. :w2:
Then I switched over to the stereo setting and man Wham! Now that's cool!
Speaking of Wham;
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More Maggi vibrato;
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1 more Lonnie Mack Maggi vibrato;
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That's quite a sound! Neat.