Magnatone Vibrato/Reverb build Project

[wsscott]

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.

[PRR]

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

[wsscott]

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.

[terminalgs]

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


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).

[wsscott]

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

[wsscott]

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.

[shooter]

guessing;

[wsscott]

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.

[shooter]

taking the power amp out of the Magnatone's circuit

yup, that's the part that got overlaid 

[sluckey]

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.

[wsscott]

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

[shooter]

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 

[terminalgs]

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?

[wsscott]

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.

[shooter]

sounds like it's color'n time, sharpen 'em up and draw it up  or if you're a digital wonk, draft it up. 

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.

[wsscott]

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.

[shooter]

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

[wsscott]

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.?

[sluckey]

The 4FB3A1B tank will work with the M10-A amp. AES sells it.

[wsscott]

Thanks for the lead. 

[66Strat]

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

[sluckey]

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! 

[wsscott]

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. 

[wsscott]

SLuckey-One more question, what power transformer would be good for this project?

[vampwizzard]

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 .

[wsscott]

Yes, I got a set of 2 pair of varistors. Thanks for the information though.

[sluckey]

250-0-250 @ 70mA and 6.3 @ 2A

https://www.hawkusa.com/manufacturers/hammond-mfg/power-products/power-chassis-mount-transformers/269jx

[wsscott]

Thanks.

[wsscott]

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?

[sluckey]

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. 

     https://el34world.com/charts/Schematics/files/Magnatone/Magnatone_m10a.pdf

[shooter]

 

much better

[shooter]

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

[wsscott]

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

[wsscott]

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?

[wsscott]

Maybe I could use this preamp section from the Magnatone M2 circuit to give me a tone and volume control for the unit?

[sluckey]

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.

[wsscott]

Thanks.  I appreciate the candor. 

[wsscott]

Sluckey-did you draw a layout diagram for your M-10A like you did for the M-2 that you would share?

[shooter]

read all about it here 10 cents please 

http://sluckeyamps.com/magnatone/magnatone.htm

[wsscott]

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.

[sluckey]

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.

[shooter]

+1
anything less you'll wind up where I did in my early learn'n days
even posting the results for a good laugh 
(It worked well, wound up making 4 or 5 amps from the parts after I gutted it :)

[wsscott]

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

[sluckey]

All pots are audio (log) taper.

[wsscott]

Thanks again for your time, and patience.  Stephen

[wsscott]

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.

[sluckey]

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.

[wsscott]

Thanks again.  What are your recommendations for the capcitors?  I'll check out the DIY Layout Creator you mention.  What is Visio?

[sluckey]

I like xicon caps and Illinois electrolytics. Visio is the program I used to make pretty schematics and layouts. Use google to tell more.

[wsscott]

Are they ceramic or film for the non-electrolytic ones?