Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: samato on August 18, 2010, 12:08:35 pm
-
Samato has a question about this post:
http://www.el34world.com/Forum/index.php?topic=5513.0
I just found and joined this forum today. Wow, am I happy I did! This is exactly what I want to build - a single channel, single input, no reverb/vibrato Deluxe Reverb. I thought it was going to be much harder and very time consuming to get the design/schematic/layout thing but here it is, already done for me. Thanks to all who participated and to this forum for making it available.
I am a beginner and have never built an amp before. I'm an audio engineer and I did study electronics but never really "got it". Recently I've started studying again and it's working out better this time. I do have good soldering skills at least.
Questions:
1) Why was the extra pair of 6L6's added? I don't think I'd want that as I want this thing to be as simple and small as possible.
2) What other changes do I need to make if I drop the "Mid" pot?
3) Would making the changes listed in the 3rd post of this thread make the circuit the same as the original Vibrato channel? That's what I would want I think. I'm not clear on the differences between the two channels on the original AB763 Deluxe Reverb but I know I always preferred plugging in to the Vibrato channel even without the effects on.
4) The Rectifier tube is a GZ34, right?
5) Shouldn't there be a 68K resistor on the input to the grid of V1 and a 1M resistor on the actual input jack? I'm probably missing something here but I don't even see the input jack. Is it just assumed that the builder would know what to do there? Sorry, newbie here.
I would greatly appreciate any help/advice/etc. you guys may be able to offer on this project. I know it is extremely ambitious on my part to think I can tackle this as my first amp build but it will be well worth it if I can pull it off. If I can't it will be an excellent learning experience (as long as I don't electrocute myself!).
I will gladly document my progress by posting diagrams, explanations, photos, and sound clips here (assuming that is acceptable on this forum).
Thanks
-
1) Some AB763 have four power tubes like Twin Reverb others have two like Deluxe or Super Reverb
2) Look at a Princeton Reverb tone stack. However, I would recommend the mid pot.
4) This layout (below) uses a solid state rectifier. You can build one with a GZ34. Look at a Deluxe Reverb
5) Look in Hoffman's Library of Information about input jacks to answer this question
Welcome to the forum!
With respect, Tubenit
-
Thanks Tubenit for moving/re-posting my questions.
1) I knew the AB763 circuit was found in other amps but I didn't put 2 & 2 together, now I get it.
2) I will consider the mid pot. It's just that in the time I spent playing though a 70's Silverface Deluxe Reverb I don't remember ever thinking "Man, I wish I could adjust the mids". From what I've been reading it seems like the key to getting the best sound out of an amp is simplicity and having the least amount of parts necessary to do the job.
4) Solid state rectifier, got it.
5) Aha, the "common hookups" page! Thanks, that is very helpful.
http://www.el34world.com/charts/CommonHookups.htm
EDIT - Simplicity and using the least amount of parts is probably not the key to the best sound but at least a very important part. I realize the quality, type, value, etc. of those parts is extremely important but that is a much more complex part of the equation I think.
-
My suggestions:
Give a load of thought to the "non-schematic" (primarily the physical form factor) aspects of this project.
A: what flavor of chassis you are going to build this on?
B: Are you going to move this around?
C: Would you like to end up with a one-piece amplifier/speaker/cabinet that you might be able to take to a jam or leave in your home without fear that someone might zap themselves on it?
I don't propose to interview you about these aspects, I'm just suggesting that you spend some time pondering them. An amp is not just a schematic manifested into an assemblage of parts.
I bring this up because I am kind of returning to tube amp repair and construction after about a 35 year hiatus. I have zero resistors lying around except for maybe two that I could cut out of a dead PC power supply and they are probably .17 ohm 5 watters. Useless. I have no drill press. I have no jars of 6-32 machine screws around. I certainly don't have a chassis punch set. I don't even have a proper workbench without having to sit on the fender (no pun intended) of a car when the car is garaged. I have a soldering iron, solder, some very high quality multiple colors of 18 ga wire which is irritatingly too big, most hand tools, and a Fluke 77 meter. My point is, that starting afresh here, I can't take anything for granted. There are no TVs in the garbage I can get a few parts out of. There aren't any terminal strips or fuseposts or pilot light holders lying around...unless I buy them. Not one, not one single part is just waiting around, eagerly waiting to be put into use.
And...if I solved each and every one of those problems, then I could theoretically build a working 5-sided chassis with open bottom = shock hazard and be in a rough position as far as bringing it to a jam without trashing it. No cabinet, no speaker.
If that situation resembles yours, I'd strongly suggest buying either a kit for a whole amp and adding/subtracting the dozen parts that would constitute the difference. OR, buying a used amp and tearing its guts out and rebuilding it. Plenty of advice here in your new home.
Never mind the cost of sourcing every part from scratch, which is well known to be higher than buying an existing amp. It doesn't get you the cabinet and speaker (unless, of course, you buy those, and you can, and they are plenty expensive)
-
Those are all valid points. I have given thought to most of them. I can't say I've got it all figured out but I don't see that as a reason not to go for it. There are cost effective ways to obtain all the necessary parts, materials, tools, etc.
I just can't justify spending all the time, effort, and money that would be required to build an amp if there's not at least a chance it will be the one I want. I know the kits are a much more logical approach for someone with my experience/knowledge but they don't offer what I'm looking for and they are, in my opinion, very expensive. I'm estimating my costs for this project to be somewhere around $300:
$100 - transformers
$50 - speaker
$50 - tubes
$50 - components, wire, and hardware
$20 - chasis
$20 - wood to build cabinet
$10 - speaker grill cloth (or other suitable fabric)
---------
$300 - Total
Hopefully I can do better by being creative with certain things but others will probably cost more than I think so that will probably offset any savings.
The schematic/layout diagrams are my focus at the moment because I can't plan or start anything without them.
-
I have converted Bogen amps into excellent guitar amps for under $100.
Having said that, I typically think of $375-450 for a combo amp scratch build.
With respect, Tubenit
-
$450 is a lot less than I can get a good Deluxe Reverb for, even a reissue. Plus this one will be the size I want.
One of the reasons I think I can save some money is the fact that this place is 15 minutes from where I live:
http://www.skycraftsurplus.com/electronics.aspx
They have a huge selection of capacitors, resistors, wire, hardware, and even transformers. The prices are pretty low.
Speaking of transformers - looking at the section Skycraft has of them (see attached photo, this is a small part of that section), I've got to believe there are some in there I could use for my amp. My question is assuming I can choose the right ones and test them (very big assumption at this point), would it make sense? Maybe even just temporarily to get the thing working and replace them if it seems like they are making the amp sound bad?
-
My Gawd, an actual surplus store..? I didn't think those existed any more. When I started out I could take a bus to Radio Row, on Canal St, in NYC. For a 10 year old, that was heaven. After they tore that out & built the WTC, I moved to California, LA, and there were some great surp places around Burbank Airport in LA and Oakland Airport in northern CA for the next 25 years. Those are now all gone.
That store looks GREAT as far as tranny selection! You're probably not going to get anything resembling a decent audio output tranny there, but a PT certainly looks possible. If you find something that puts out enough for a tube amp, the chances of it having a dedicated bias tap are close to zero. All that means is that you derive bias from one of the HV legs.
In my career, the number of bad transformers I've encountered has been remarkably low, if we can agreee to discard ones that are obviously flamed out and dripping goop. You've got a nice selection there, you probably need to do a drive-by to see if there are any that put out more than 60 volts!
Your task to be able to estimate current capacity from size; without buying a 45 pound beast!
-
I prefer to just buy the right transformers and get it right rather than make a questionable transformer from a surplus store work.
Here's an AB763 Deluxe Lite that may interest you.
http://home.comcast.net/~seluckey/AB763_Deluxe_Lite.pdf
EDIT... fixed broken link.
http://home.comcast.net/~seluckey/amps/misc/AB763_Deluxe_Lite.pdf
-
I prefer to just buy the right transformers and get it right rather than make a questionable transformer from a surplus store work.
Here's an AB763 Deluxe Lite that may interest you.
http://home.comcast.net/~seluckey/AB763_Deluxe_Lite.pdf
That does indeed appear to be closer to what I'm looking for. I'll be studying it for a while.
Would anyone care to comment on how this AB763 Deluxe Lite compares to/differs from the original AB763 Deluxe Reverb design? All I can see at first glance is that it's single channel, the addition of a mid pot, and the lack of reverb/vibrato.
I'm also still trying to figure out if there is much difference in the original AB763 Deluxe Reverb's two channels, aside from the reverb & tremolo on the Vibrato channel.
-
Would anyone care to comment on how this AB763 Deluxe Lite compares to/differs from the original AB763 Deluxe Reverb design? All I can see at first glance is that it's single channel, the addition of a mid pot, and the lack of reverb/vibrato.
In addition to your observations, it has a bright switch/cap and the .1µF coupling caps between the PI and PA have been replaced with .047µF caps. R14, 270K, replaces the missing 220K mix resistor and 50K INT pot. Other than that, it's exactly the same as an AB763 DR, but with the VIB channel, reverb, and trem circuits stripped out.
I'm also still trying to figure out if there is much difference in the original AB763 Deluxe Reverb's two channels, aside from the reverb & tremolo on the Vibrato channel.
Well, the VIB channel has an additional gain stage. V4B restores the gain lost due to the way the reverb circuit ties in. I've heard that the VIB channel is slightly hotter than the NOR channel, but my hearing is not good enough to detect a difference and I won't be putting a scope on it to see if there's a measurable difference. One other slight difference, the VIB channel has a permanent bright cap and the NOR channel has none.
-
OK, sluckey types more quickly and less than I do... :lipsrsealed:
I'm also still trying to figure out if there is much difference in the original AB763 Deluxe Reverb's two channels, aside from the reverb & tremolo on the Vibrato channel.
Yes, there is a significant difference. Look at the shaded area in sluckey's schematic. That's the "Normal" channel signal path. Now look carefully at the Vibrato channel's signal path in the AB763 schematic (print it out from Doug's Library and use a highlighter). Instead of what's shown on sluckey's schematic in the shaded area, you'll see a 3.3 meg resistor in parallel with a 10pf cap and an additional gain stage before the input to the phase inverter. Actually, the attached preamp schematic (also from sluckey) shows it much more clearly.
The important thing to understand is that the 3.3 meg resistor forms a voltage divider with the 220K resistor going to ground at the right-hand end of the reverb circuit. That results in about a 94% signal reduction before it goes into the "extra" triode.
(technically, the bottom portion of that voltage divider actually is the 220K resistor in parallel with the combination of the 470K resistor attached to the Reverb pot and the lower "leg" of the Reverb pot - effectively only 150K with Reverb at "0", yielding a 95.5% signal reduction)
Sluckey's "Deluxe Lite" looks like a really neat, clean circuit. However, that extra triode does add something to the circuit's tone IMHO. One possibility would be to "steal" a triode from the reverb driver to get that extra gain stage add a 12AX7, use one triode for the additional gain stage and the other for Princeton Reverb type tremolo, but that would require some design experience and a fair amount of experimentation. Or use two triodes of a lower gain tube like a 12AU7 in parallel where the added gain stage is. Alternatively, you could add two 12AX7s and build sluckey's "Tweed" Deluxe Reverb using 3 triodes for the reverb and the 4th for the added gain stage.
Hope this helps,
Chip
-
Thanks guys for all the input and thank you Sluckey for posting the diagrams. It will take me a while to catch up to what you're saying and what the sonic results might be but when I do I'll have some more questions.
-
On a different note, what do you guys think of one of these Rola 12", 8-ohm speakers for this amp? I can get them pretty cheap. I'm told they came out of a Hammond organ. I can test them before buying, though maybe only through the organ.
-
On a different note, what do you guys think of one of these Rola 12", 8-ohm speakers for this amp? I can get them pretty cheap. I'm told they came out of a Hammond organ. I can test them before buying, though maybe only through the organ.
Depends what Rola speakers they are. Some rola/'celestion' type speakers are pretty variable. Specs of their old line here:
http://www.retrovox.com.au/rola.html
-
I went ahead and bought 3 of those speakers, would've been 4 but he accidentally ripped one of the cones while I was there. I really don't know if they are Rola or what but they are very lightweight and don't look like anything special. They sound pretty good though. We put each one, one by one, into an empty home stereo speaker cabinet with the back off and connected them to my Fender Pro Jr. I also checked DC resistance and all were around 8-ohms. Nothing sounded blown so I figured I can't go wrong for $20. I might have to make a cabinet for the big one and run my Pro Jr. through it at home when I have band rehearsals because it sounds pretty good and seems to have less volume than what I have in there now which is too loud.
He also gave me some sort of 9-pin, 12ax7 type tube. The letters have been rubbed off so I don't know exactly what it is. I also took the opportunity to dig through one of his trash cans and picked out a few circuit boards populated with components. I know I probably won't be able to use a lot of those, if any, but I figured it couldn't hurt. One board has a bunch of carbon comp resistors and big orange drop type caps.
Question about extension speaker cabinets: If I want as small as possible it would probably be best to make it open back or at least partially open, right? It seems like most people go with closed but that probably doesn't work well for the small size I want to have, with not much room to move air behind the speaker.
-
samato,
I think you got a great deal on the speakers, they're probably around 20 watts each. Too bad you lost the fourth but if you get an OT with 8 and 4 ohm secondary, two should handle 6V6's but I'm not sure about 6L6's.
Wish I could find a hit like you got, not too much in my area except Craigs List.
al
I prefer to just buy the right transformers and get it right rather than make a questionable transformer from a surplus store work.
Here's an AB763 Deluxe Lite that may interest you.
http://home.comcast.net/~seluckey/AB763_Deluxe_Lite.pdf
Can I ask where the filtering is located in your Deluxe lite? I assume hanging under the chassis enclosed in a metal box like some Fenders? Could I put the filtering on the board if I'm careful with my grounding?
al
-
Hmm, so you think I would blow the speaker if I tried to go with two 6V6's, 8-ohm OT, and just one of those speakers? You're probably right about them being rated at around 20 watts, I figured somewhere between 15-25 watts. The Deluxe Lite puts out around 22 watts, right?
I'm only planning on having one speaker in the amp, and maybe an extension cabinet sometimes. I like to travel light. I carry my current rig with guitar, amp, couple pedals, cables, etc. on my motorcycle.
-
Can I ask where the filtering is located in your Deluxe lite? I assume hanging under the chassis enclosed in a metal box like some Fenders? Could I put the filtering on the board if I'm careful with my grounding?
I never built the Lite. Instead, I built the DR Vibrato channel with reverb but no trem. The filter caps are located on top of the chassis. That special layout uses a slim board that fits neatly inside a Hammond 3x4x17 chassis and the chassis is a perfect fit for a 5E3 Deluxe cab.
You can put the caps directly on the board if you have room. I prefer to do that. However, I was trying to stuff a lot of circuitry into a tiny space and did not have that option. My goal was to put a single channel DR with reverb into a 5E3 cab. Here's a link so you can see the challenge...
http://home.comcast.net/~seluckey/amps/tdr/tdr.htm
BTW, printing that layout full scale produces an exact size board layout that can also be used as a drill template.
-
Hmm, so you think I would blow the speaker if I tried to go with two 6V6's, 8-ohm OT, and just one of those speakers? You're probably right about them being rated at around 20 watts, I figured somewhere between 15-25 watts. The Deluxe Lite puts out around 22 watts, right?
Yeah, you would blow a single speaker with 6V6's, you'd need about a 30 watt single from my experience. It's the distortion that will blow it, if you keep it clean you might be OK but that's impossible :laugh:
A Princeton Reverb has two 6v6s and runs 15 watts, I believe. I know the Deluxe Reverb is 22, I could never figure that out.
I never built the Lite. Instead, I built the DR Vibrato channel with reverb but no trem. The filter caps are located on top of the chassis. That special layout uses a slim board that fits neatly inside a Hammond 3x4x17 chassis and the chassis is a perfect fit for a 5E3 Deluxe cab.
Here's a link so you can see the challenge...
http://home.comcast.net/~seluckey/amps/tdr/tdr.htm
BTW, printing that layout full scale produces an exact size board layout that can also be used as a drill template.
Thanks for the info, nice to know a Hammond chassis (3x4x17) fits a 5E3, I have one and you see Hammond chassis all the time on fleabay and Craig's List. Thanks for the link. I love the 15 to 20watts you get with 6V6s and the tone, EL84's are OK but you don't get that tight bass.
al
-
A Princeton Reverb has two 6v6s and runs 15 watts, I believe. I know the Deluxe Reverb is 22, I could never figure that out.
Different voltages, different phase inverters, and, probably most importantly, different output transformers.
Chip
-
I guess I didn't need to buy those speakers then. I only got them so I would have one to put in the amp I'm building, knowing that I might upgrade it at some point. Oh well, maybe I'll make a 2 x 12 extention cabinet just to have around. It would be 4 or 16 ohms though.
-
Hey Sluckey - any chance you could send me your Deluxe Lite Jshem file, assuming that's what you used to make it?
-
OK, sluckey types more quickly and less than I do... :lipsrsealed:
I'm also still trying to figure out if there is much difference in the original AB763 Deluxe Reverb's two channels, aside from the reverb & tremolo on the Vibrato channel.
Yes, there is a significant difference. Look at the shaded area in sluckey's schematic. That's the "Normal" channel signal path. Now look carefully at the Vibrato channel's signal path in the AB763 schematic (print it out from Doug's Library and use a highlighter). Instead of what's shown on sluckey's schematic in the shaded area, you'll see a 3.3 meg resistor in parallel with a 10pf cap and an additional gain stage before the input to the phase inverter. Actually, the attached preamp schematic (also from sluckey) shows it much more clearly.
The important thing to understand is that the 3.3 meg resistor forms a voltage divider with the 220K resistor going to ground at the right-hand end of the reverb circuit. That results in about a 94% signal reduction before it goes into the "extra" triode.
(technically, the bottom portion of that voltage divider actually is the 220K resistor in parallel with the combination of the 470K resistor attached to the Reverb pot and the lower "leg" of the Reverb pot - effectively only 150K with Reverb at "0", yielding a 95.5% signal reduction)
Sluckey's "Deluxe Lite" looks like a really neat, clean circuit. However, that extra triode does add something to the circuit's tone IMHO. One possibility would be to "steal" a triode from the reverb driver to get that extra gain stage add a 12AX7, use one triode for the additional gain stage and the other for Princeton Reverb type tremolo, but that would require some design experience and a fair amount of experimentation. Or use two triodes of a lower gain tube like a 12AU7 in parallel where the added gain stage is. Alternatively, you could add two 12AX7s and build sluckey's "Tweed" Deluxe Reverb using 3 triodes for the reverb and the 4th for the added gain stage.
Hope this helps,
Chip
Okay, it took me a while but now I understand what the explanation above means and I have made a decision based on it. Even though I can hear the difference between the Normal & Vibrato channels on a Deluxe Reverb and prefer the sound of the latter, for this build I will go with the Normal channel but maybe add the permanent bright cap. Adding an additional gain stage complicates things, adds to the cost, and gets away from the idea of keeping things as simple as possible. Besides, the Normal channel still sounds great on that amp.
-
any chance you could send me your Deluxe Lite Jshem file, assuming that's what you used to make it?
It's a Visio file.
-
any chance you could send me your Deluxe Lite Jshem file, assuming that's what you used to make it?
It's a Visio file.
Oh - and that probably can't be imported into Jshem, right?
-
I'm thinking about buying a Super Champ XD to convert into this modified Deluxe Reverb I want to make. I think I can get the SCXD pretty cheap, maybe around $150 or less. Here are the specs:
http://www.fender.com/products/search.php?partno=2331100000
It seems like I could use the:
power and output transformers
3 tubes - 12AX7, (2) 6V6
jacks
chasis
cabinet
If so all that would be left to buy would be:
choke
2 tubes - 12AT7, GZ34
turret board, turrets, tool
components - capacitors, resistors
pots
wire
I don't know if I could fit a 12" speaker in the SCXD cabinet and I'm probably missing a few things but overall does this sound reasonable to you guys?
-
That conversion would be a difficult challenge for a beginner. You will have to do a lot of circuit modification to use that PT. Forget using a tube rectifier with it. You'll have to use a bridge. And you'll have to figure out how to get your bias voltage too. It can be done, but will require some good electronics knowledge.
The tubes and OT could be used. Maybe the chassis can be used too. You'll need new jacks.
I think if you watch ebay, you can find a much better conversion candidate, especially for a first time project.
http://support.fender.com/schematics/guitar_amplifiers/Super_Champ_XD.pdf
-
Thanks, I won't waste my money and time on that one then.
-
Hey Sluckey - Question about your Deluxe Lite diagram:
R14 is 270K-ohm 20% tolerance. The original Fender "Deluxe Reverb-Amp AB763" calls for 27K-ohm 10% in this position. Is this an intentional change you made? Am I reading something wrong here? If intentional what is the reason?
Thanks
-
Hey Sluckey - Question about your Deluxe Lite diagram:
R14 is 270K-ohm 20% tolerance. The original Fender "Deluxe Reverb-Amp AB763" calls for 27K-ohm 10% in this position. Is this an intentional change you made? Am I reading something wrong here? If intentional what is the reason?
Thanks
Don't sweat the tolerance rating - 10% is better than 20% and 5% is better than both.
The "R14" 270K resistor replaces the combination of the 220K mixing resistor plus the 50K Intensity pot in the stock AB763 circuit. I couldn't find a 27K resistor in the AB763 circuit, but there is a 22K close by in the phase inverter (R16 in sluckey's Deluxe Lite). Perhaps I'm missing something though...
Chip
-
The 27K-ohm resistor (at least that's what I think it says) is at the bottom right hand corner of the box I inserted in this cutout of the layout diagram of the Deluxe Reverb AB763.
-
R14 is 270K-ohm 20% tolerance. The original Fender "Deluxe Reverb-Amp AB763" calls for 27K-ohm 10% in this position.
No it doesn't. There is no such resistor in the original. Chip explained the purpose of my R14, 270K and I discussed it very early in this thread.
EDIT... I didn't spec any resistor tolerances. I only use 5% CC resistors. I didn't put a tolerance band (for convenience) on my layout resistors. I know that in the real world that the absence of the tolerance band indicates a 20% tolerance, but that doesn't apply for my Visio stencils. Sorry for the confusion.
-
The 27K-ohm resistor (at least that's what I think it says) is at the bottom right hand corner of the box I inserted in this cutout of the layout diagram of the Deluxe Reverb AB763.
That's an error on the layout. The schematic correctly shows a 22K value for that resistor. That's the tail resistor for the LTP PI.
BTW, there are several similar discrepancies between schematics and layouts for several of the old Fender amps.
-
Thanks guys, makes sense. I've been drawing it up, referring to the Deluxe Lite layout and the original layout mostly, but now I realize I need to check the schematics all the time too.
Would you mind taking a look at what I have so far and letting me know about any problems you see? I've only gotten up to PI/driver stage so far. I'm still a little confused about the part with the coupling cap C6 and R9, R10 - does that look right?
Also, I should remove the .047-600 cap on the ground switch right?
-
Also, I should remove the .047-600 cap on the ground switch right?
Please remove the ground switch and that "death cap". Use a 3-prong cord. Wire the fuse & switch as shown in sluckey's documents.
Chip
-
I'm still a little confused about the part with the coupling cap C6 and R9, R10 - does that look right?
yes
-
Here are a couple layouts for you.
Single channel, ab763, no reverb, no vibrato.
-
Thanks for those layouts. I'm actually learning a lot by drawing it out myself but it really helps me to be able to refer to diagrams that are known to be correct.
I'll have a lot more questions soon. I'm anxious to start the build but I have more to learn before I'll feel comfortable, besides I still need to get the money together to fund the project.
-
Hey topbrent - That's some pretty good editing work to make those diagrams. They look exactly like the originals but without the other stuff, which is all I want obviously.
I noticed the plates on your V1 are running at 170V and on the PI it's 180V. The original has V1 at 180V, the first triode of the PI at 170V, and the second triode at 180V. I guess this is from a different version than I'm looking at. What is the cause of this change, something different with the power supply?
-
Don't worry about 10 volts DC on the power rail.
-
Just wanted to post what I have so far of this diagram. If anybody sees any errors please let me know. Thanks.
-
Your R18 should be 82K. Look at the Fender schematic rather than the layout.
http://www.schematicheaven.com/fenderamps/deluxe_reverb_ab763_schem.pdf
This layout has it correct...
http://www.schematicheaven.com/fenderamps/deluxe_ab763_schem.pdf
-
Thanks Sluckey. Once again I'm guilty of looking at just the layout and not the schematic even though I know better! If that's all I messed up so far that's pretty good for me though.
-
Redrawing the layout is the perfect way to become intimate with that circuit. And that's a good thing. Keep it up.
-
170V, 180V, 100K, 82K, 20%, 5%......
Bah. This isn't a moon rocket, where 10km means you miss the moon completely. It will play well at 150V or 200V. It will play well with 100K+100K in PI plates, though theory suggests a slight unbalance roughly correctable if the near-side load is ~~20% low.
Resistors used to be made like bricks: a pot of clay with a handful of sand for bricks or coal-dust for resistors. One brick may be 20% softer than another, do you really care as long as the house stays up? Old radios used the cheapest 20% tolerances, most guitar amps are from days when 10% was most available, today 5% are cheap and 2% is cheep-enuff.
But 2% is not "better". The designer will assume some tube values (which really vary +/-20% or more) then do his math. If he had that specific assumed tube, the perfect resistor might be 113,456 ohms. However anything from 75k to 150K works too, and so close you may be unable to tell a difference.
Where Sluckey had a missing band, he meant "use your your cheapest or favorite color". When Silver (10%) was cheapest, that's what we had. Gold is prettier and today you can't find Silver as a commodity resistor, so use Gold. Or if 2% are being dumped cheap, use 'em; but don't think that 98K-102K is "better" when the amp will work a treat with 95K-105K, 90K-110K, even 75K-150K.
And a different designer might have favored 200K. 270K and 470K were favored in radio audio amps: you lose a hair of treble but get a bit more gain below 4KHz and use less power (cheaper filtering). Fender did that, then moved to 100K. He may be right; this is the most-copied value on the planet. But Gibson and Ampeg sold a bunch of amps with other values, and using other values is a popular tweek.
-
Yeah, I don't plan to be that anal about choosing my parts but I figure I should at least draw (or copy) the circuit accurately - going by the original or if I'm making changes they should be for a good reason.
I realize there is a "+ or -" tolerance for all parts & values, it says so on the schematics & layout diagrams.
-
I'm driving myself crazy trying to figure out how the power supply, OT, and choke sections of this circuit work. My brain hurts too much to formulate any specific questions right now but I figured I should post it here and see if I can get any input before I do too much damage.
-
Would you guys be so kind as to have a look at my "completed" diagram and let me know if I have it right? I guess this is a combination of a schematic and a layout diagram. I wanted to have something easier for me to follow, with everything very obvious. I hope it's not too hard to read. I can try to post a higher resolution file if necessary.
I'm mostly concerned about the AC, power supply, and heater wiring but I'm not 100% sure about any of it so any help would be greatly appreciated.
-
AC cord needs 2 more wires. :wink:
-
Ah yes, I forgot those - thanks. That's it? Everything else looks right?
-
While I'm still trying to make sure I have the design right I'm also starting to think about what would be the best size/shape of chasis to use for this project and could use some input from people with experience.
Keep in mind my goal is to keep this thing as small as is reasonably possible. My Fender Pro Jr. and Vox Pathfinder 15R are pretty much ideal in the size department. This amp may need to be a little bigger because I plan to use a 12" speaker, though I'm not 100% sure about that yet either. I plan to make the amp first and find some safe way to mount it or support it while I try different speakers/cabs. I'll build the cabinet after I make a decision on the speaker to use.
I originally thought a chasis like the one on my Pro Jr., with the knobs on top, would make the most sense because the chasis doesn't extend all the way to the front which might leave more room for mounting a speaker. Now I'm not sure. The knobs on the front type might be actually leave more speaker room because the transformers can be more toward the back, though the speaker has to be a little lower. Can anyone shed some light on this for me?
Any recommendations on what would be the smallest and best shape chasis to use for this? I can't afford a nice, pre-drilled one. I'll be going with a blank one most likely so size and money are both major factors.
-
I highly recommend a 12" speaker with this amp. I used a Deluxe 5E3 cab and a Hammond 4"x3"x17" chassis. Makes a neat package. If you want a combo, spend some time planning the cab, chassis, and speaker before you actually start this project. Here's mine...
(http://home.comcast.net/~seluckey/amps/tdr/s_tdr_11.jpg)
-
That is a beauty for sure but it looks like it could be smaller, even with the 12", don't you think? Mine will also have less parts. The reason I'm so crazy about keeping it small is I'm really enjoying traveling to gigs on my motorcycle and walking in with a guitar in one hand, amp in the other, and a bag with cables & stuff over my shoulder. I'd hate to give that up as I usually don't drive my truck unless I have to so I'm saving a lot in gas money this way plus it's more enjoyable.
I agree that I need to plan the whole package before starting the project. So would you say that type of chasis and overall layout/topology/whatever you call it is the most space saving?
-
Like Sluckey's awesome Tweed ab763 and AB763-lite builds, you can stuff it all into a very small tweed style chassis if you keep your layout tidy.
Some folks seem to think that the leads on components must stick out 2" on each side for it to be "correct".
- If you move away from that style of layout thinking, you will surprise yourself at how much amp you can stuff in a small space.
- You can put the whole ab763 preamp on a few small terminal strips and eschew the eyelet board topology, also.
- Using Xicon MPP caps like Doug sells make stuffing an amp in a small chassis much easier. (IMO, they sound great, also)
Good lead dress becomes much more critical in smaller chassis', though.
Here is a fun single channel AB763 amp stuffed in a chassis about the size of tweed deluxe.
Dumble style mid boost on the switch, and a power supply sag resistor.
Although this layout started out as another manufacturers layout design, but I cut, modified, folded, spindled, boiled, pickled, mashed, diced and chopped it to ab763 specs.
Note: Although I forgot to include in this layout the 820 ohm NFB resistor, and .001 PI coupling cap :rolleyes:: :wink:, this is a fully tested, working layout.
-
Thanks for posting that Topbrent. Do you have any pictures and/or sound clips of that amp you could post?
What Sluckey posted above is the size of a Tweed Deluxe chassis, isn't it? It seems like mine could be smaller, especially if I follow your advice on how to save space on the board - or would the tubes be too close together if I go smaller than that?
-
5E3 chassis dimensions are 14 5/8" long x 4 1/8" high x 2 5/8" deep. Scratch building anything in this narrow chassis will present some real layout challenges that you wouldn't see if using a 6 to 7 inch wide chassis. And you will have to carefully plan each stage of the build. A wider chassis will make the layout design and build sequence much easier.
-
5E3 chassis dimensions are 14 5/8" long x 4 1/8" high x 2 5/8" deep. Scratch building anything in this narrow chassis will present some real layout challenges that you wouldn't see if using a 6 to 7 inch wide chassis. And you will have to carefully plan each stage of the build. A wider chassis will make the layout design and build sequence much easier.
I believe that. Still, I'm stuck on the small size approach. I always seem to make things difficult for myself so why should this be any different?
Are these the Xicon MPP caps Tobbrent was referring to?
-
Thanks for posting that Topbrent. Do you have any pictures and/or sound clips of that amp you could post?
What Sluckey posted above is the size of a Tweed Deluxe chassis, isn't it? It seems like mine could be smaller, especially if I follow your advice on how to save space on the board - or would the tubes be too close together if I go smaller than that?
Here is what one looks like built up using huge Jupiter caps. This was built by tlainhart.
I have changed the circuit around a bit since this pic was taken and have removed all of the Jupiter caps and installed the Xicon MPP caps.
- can't tell a tonal difference....Sure is nicer to work around in that cramped chassis, too.
(http://www.hoffmanamps.com/MyStore/catalog/images/IMG_2440.jpg)
-
Bare chassis and board.
-
I've built 3 amps in the Hammond 3x4x17 chassis. I used Doug's board material for all, but I ripped Doug's standard width of 3 1/8" down to 2 1/4" or 2 5/8". Using the narrower board was very helpful when it came time to put it all together.
-
With a circuit this simple, you could easily stuff all of this into a blackface/silverface champ sized chassis, also.
Reproduction champ chassis are available from Marsh, MOJO and Allen.
Get a nice larger 12" baffle combo cabinet from Allen, MOJO, mathercab.com, JDNewell, and you could have a powerful amp in a small package. Load it with a very efficient speaker for the maximum effect, 100db+ sensitivity speaker.
http://allenamps.com/minichassis.php
(http://allenamps.com/images/chassis_bottom.jpg)
(http://allenamps.com/images/project_chassis3.jpg)
-
Use a vertical mount PT instead of a horizontal - thru chassis PT , and you'll have a lot more room inside the chassis.
-
Use a vertical mount PT instead of a horizontal - thru chassis PT , and you'll have a lot more room inside the chassis.
I'm not sure I know what that means. Here is the PT I was thinking of using:
http://store.triodestore.com/deretrvipotr.html (http://store.triodestore.com/deretrvipotr.html)
-
I'm trying to figure out which resistors, if any, I should upgrade to a higher power rating on this amp. From my drawing above, would it be making R23 & R25 2W instead of 1W and R24 & R26 1W instead of 1/2W - keeping the values the same?
Should I do this and are there other proven, known issues that I should be aware of? I really don't want to change anything from the original design unless it seems necessary for the sake of reliability & safety.
-
Okay, I found the answer here:
http://www.el34world.com/charts/fenderservice1.htm
Guess I should have researched a bit more before posting. Hoffman suggests that R23 & R25 should be 3W and away from the tube sockets.
-
Sluckey's Deluxe Lite schematic clearly shows the resistors which need to be over 1/2 watt ratings. The original AB763 schematics also show resistor ratings in specific spots but Fender was cutting things a bit close at times. Don't forget that the bias "range resistor" needs to be 1 watt or greater. Also, make sure your 1 ohm bias measurement resistors are 1-watt, flameproof, and 1% tolerance (it does matter there).
Lastly, I've got it in my head that capacitors generally only need to be rated for 400 volts except for the coupling caps between the PI and the power tubes. Don't know where I got that idea...
Chip
-
The problem I have when looking at other people's designs is when I see changes from the original I don't know why they were made - for a different sound, to fix a known flaw, etc.
I have some 16mfd, 1000V caps I was thinking of using where the schematic calls for 16mfd, 450V. Would this be a problem, other than the fact that they are physically larger and take up more space. Would the amp respond differently - less "sag" or "squash" maybe? I don't want that, I like the sag of the original but those caps are $10 each so if I can use what I have...
-
hello all. Here is my version of AB763 showman "lite". Waiting on head cab. Stone quiet and
sold as soon as done. 18x8x2" chassis, All Hoffman Iron.... Wish I kept that one. oldgitar335
-
The problem I have when looking at other people's designs is when I see changes from the original I don't know why they were made - for a different sound, to fix a known flaw, etc.
I have some 16mfd, 1000V caps I was thinking of using where the schematic calls for 16mfd, 450V. Would this be a problem, other than the fact that they are physically larger and take up more space. Would the amp respond differently - less "sag" or "squash" maybe? I don't want that, I like the sag of the original but those caps are $10 each so if I can use what I have...
Samato, Just a little advice:
IMHO, just because you have invested some money in a particular set of components and have them on hand, don't feel like you are required to base your build around them just because you have them. As a new builder, this pathway of thinking will handicap you more often than help.
If the build is unsuccessful and you need help, it is much easier for the experienced techs to help you diagnose the problem if you have followed a proven design with traditional parts.
Due to the simple circuit and low parts count, the list of caps and resistors for the amp you are planning is pretty inexpensive, really. The real money in home building an amp is in the transformers, chassis, cabinet, and speaker.
Save or sell the other parts.
-
Still, I'm stuck on the small size approach.
If that's still your goal then don't use huge over-rated parts.
The problem I have when looking at other people's designs is when I see changes from the original I don't know why they were made
Do you mean the Deluxe Lite? I kept the circuit as near identical to the original as I could. I used 20µF or 22µF power supply caps simply because they are more common today than the 16µFs which were common when that amp was first in production. I added the 220K bleeder resistor across the first filter cap to discharge the B+ more quickly when the amp is turned off. I added another bias cap simply for a smoother bias voltage (an improvement IMO, but certainly not necessary in a cost controlled production amp). I used a 1500Ω cathode resistor for V1B because the Lite doesn't share a cathode resistor with another tube like the original. I added 1Ω resistors to the output tube cathodes for convenience of biasing the amp (another unnecessary improvement since in Leo's time they simply used the 'set it and forget it' bias method). I added the mid pot just because I wanted one.
All the above changes add nothing (nor take anything away) to/from the actual sound or operation of the amp. They do add to the cost and that is a big concern in a production environment, but mean nothing to me as a hobbyist. If you see any other differences (other than obvious layout differences) let me know and I'll try to explain them.
My different layout was simply to make it easier to stuff into that 3x4x17 tweed style chassis. The board layout would have looked quite different if I had chosen a wider chassis. But it still would not look like the original layout simply because figuring out my own layout is part of the enjoyment I get as a hobbyist. Leo had a decent working board layout and he used a very similar layout in all his old amps. That makes for easier and faster assembly and that means more profits. I'm only gonna do this once, so profit is of no concern to me.
-
The reason I'm so crazy about keeping it small is I'm really enjoying traveling to gigs on my motorcycle and walking in with a guitar in one hand, amp in the other, and a bag with cables & stuff over my shoulder.
How exactly do you manage to transport a guitar, and amplifier, and a bag on a motorcycle?
-
The reason I'm so crazy about keeping it small is I'm really enjoying traveling to gigs on my motorcycle and walking in with a guitar in one hand, amp in the other, and a bag with cables & stuff over my shoulder.
How exactly do you manage to transport a guitar, and amplifier, and a bag on a motorcycle?
I'll have to take a picture to show it. It's much easier than it might sound through - it's all just strapped to the seat behind me. It wouldn't work on all bikes but my '98 Honda CB750 Nighthawk is perfect for this.
Sometimes I even take extra stuff like a mic stand, camcorder, and other small recording equipment.
-
I'm finally ready to get started on this build. It's taken me a while to find the time and money. I've been away from this for several months and I had just started understanding things so I'll have to go back and re-learn a lot but that's okay.
I'm going to start by ordering the transformers. Do any of you think it would not be a good idea to use these?
http://store.triodestore.com/deretrvipotr.html
http://store.triodestore.com/dedereoutr.html
http://triodeelectronics.com/40-18040.html
I know there is much "better" iron on the market and many people choose the best quality they can afford. I'm on a tight budget. Besides, I'm not sure I would prefer the sound of the high quality stuff anyway. I guess I'd just like to know if any of you have used these and what the results were.
Anyway, I plan to post my progress here and bother you guys with lots of questions. :smiley:
-
Solid choices.
If it were me ordering from that vendor, I would choose the larger 40w output transformer with 4/8/16 taps.
The larger transformers will sound more solid and will be much more future proof. (You will probably want to install 6L6 tubes at some point, right?....)
With that in mind, I would also choose the slightly more powerful Vibrolux style power transformer for the same reason.
http://store.triodestore.com/babareproreo.html
http://store.triodestore.com/trvirepotr.html
These changes will sightly add more cost to your build (~$45.00'ish), but will ultimately make your amp more versatile.
PS: Doug Hoffman sells transformers also.
-
I gave some thought to what your saying about using larger transformers. I see the benefit in flexibility and power but I don't think that's what I'm going for on this build. One of my main goals is keeping this thing as small as possible. I don't think I need or want any more power. If I can make it sound close to what a real Deluxe Reverb sounds like I'll be beyond happy.
-
Note: Although I forgot to include in this layout the 820 ohm NFB resistor, and .001 PI coupling cap :rolleyes:: :wink:, this is a fully tested, working layout.
I think it's also missing the positive connection between the 47uF and 22uF caps. Cool layout!
-
I'm coming up with a lot of questions as I'm trying to get my parts together. I'm currently wondering what the reasons are for running some wires under the circuit board and if it would be okay not to do that.
I'm considering using a small piece of wood with nothing protruding from the bottom of it. It would sit flat on the chassis so I wouldn't be able to run anything underneath.
Are the wires run underneath just to keep things cleaner or are there more important factors to consider with this?
-
You don't have to run under-board wires. I try to keep them to a minimum. You can have flying leads over the top of the circuit board, but that looks messy and could make populating the board with components more difficult.
You aren't suggesting a wooden circuit board, are you? I know that a few guys have done just that, but the potential for an electrical fire doesn't appeal to me. Besides, I'm still not skilled enough with the soldering iron that some turrets wouldn't scorch the wood around them. There's also the potential for the wood to become slightly conductive in a very humid environment, but that can happen to tag board too.
Cheers,
Chip
-
Yeah, I'm considering a wooden board. Not because I think it's better or anything, just it might be easier and cheaper in this case. I know there is potential for fire but I was doing some "testing" and I think it's highly unlikely that this piece of wood could catch on fire inside the amp. A spark is not going to do it. Maybe prolonged, direct contact to high temperature could but none of the parts on the board get that hot, as far as I know.
Basically, I was holding a lighter to the board and it was very hard to make it burn. It got scorched but would not go up in flames.
I'm also considering plexi-glass and other plastics.
-
I need some help with this.
I've been researching the theory involved in how to layout transformers, tubes and how it relates to different parts of amp circuits. My understanding is that in general it's best to have as much space as possible between the PT and the OT to reduce noise. The angle is important too. I read about the headphone trick to test for this and I might try it but it might not matter in this case because the chassis I'm trying to use is so small that there are only so many possibilities. If it really seems like it won't work I might try a larger chassis but I want to give this a shot.
The problem with moving the OT as far away as possible, as I understand it, is that at some point you face the problem of long wire runs and risk having the OT too close to the preamp circuitry - another kind of noise. So it seems this is a balancing act of sorts. Compromises must be made somewhere when you're dealing with limited space. I'm trying to find the best compromise here. Maybe this amp will be noisier than it could be because of the tight spacing but maybe the choke will help with that? Anyway, I'd be willing to deal with some noise if it's not too bad and it means I get the sound and portability I want. I'm used to dealing with a noisy Pro Jr. anyway. I've decided this will be a head, not a combo by the way.
The next 3 posts show 3 options I've come up with. My circuit board will be very small compared to most I see here and I should be able to play around with it's position. I think it should be pretty close to the front but I can slide it all the way left, toward the middle, etc. - if that helps. I'd like to hear your thoughts on what's preferable or any other options. Thanks.
-
Option 1
-
Option 2
-
Option 3
-
Option 4 - This is now looking to me like the only way that would work.
-
What is the height of that chassis? 1.5" or less? Is it high enough to mount the PT and still put the bottom cover on? And don't forget about the filter caps. They take up a lot of real estate. Building in a small chassis has it's rewards, but it can be a bitch to plan and build or work on later. I like your option 4 and think you can pull it off if you plan well.
I built 3 combo amps (including my TDR) using a Hammond 3x4x17. It's tough. I've since switched to the typical Marshall style chassis 2.5"H x 6.5"D x whatever length I need. It's a pleasure working in a chassis of those dimensions.
If you have any reservations about cramming your amp into that small chassis, just get a bigger one.
-
Chassis height is 1-14/16" (10-13/16" wide, 6-1/16" deep). I checked and it would be enough to for the PT but I'm thinking about using spacers and keeping the PT above just to have the extra room inside for other things.
I'm also thinking about using an Altoids can to put my filter caps in. They all fit but I'm a little concerned about the wire runs that would be necessary to do it this way.
I'm also wondering if it might be better to mount the choke underneath. I don't see anybody else doing that but I think I could fit it and it would allow me to get it farther away from the pots. Should this even be a concern?
I decided this will be a head. I originally wanted a combo but it's just too much to think about for me at this point. Doing it as a head simplifies things and is probably better in the end anyway. Combo amps, especially small ones, are torture chambers for tubes.
-
Got my board ready. I used a piece of what I think is some kind of fiberglass I found at a surplus store. The sheet cost $3 and I could make about 5 of these boards with it. The eyelets were done with a grommet tool I got at Harbor Freight for $2.99, with 100 grommets included.
Now I'm struggling with making the chassis holes and cutouts without the proper tools or know how.
-
Big Rookie Mistake!
I made my board layout by following the original Deluxe Reverb layout. This would've been fine with the combo amp design I was originally going for but I've since decided to make this a head. Now my board is upside down!
I think I'm going to make a new board and get it right because not only would doing it this way look messy but running the wires that go to the tubes across the wires that go to the pots and the extra wire length can't be good for noise.
Re-doing the board would be the smart move at this point, right?
-
Just do it in reverse and call it a Marshall Twin. :grin:
-
I did the same thing on my first build, ended up with a left handed 5F1 head. :laugh:
-
Yeah, maybe it's not a big deal. It's correct from left to right, I just don't like having the points that connect to the tubes being on top and the points that connect to the pots being on the bottom.
Anyway, the new board is underway. I wouldn't have bothered re-doing it if I hadn't already made the holes for the PT and power connector - I could have just moved those to the other side.
-
2 questions:
1 - The AB763 Deluxe Reverb schematic calls for a 250K-A pot for the Treble control. All I have on hand at the moment is a 500K-A. What differences can I expect if I use the 500K-A pot?
2 - Does the layout of the tubes & transformers below look like it will cause problems with heat? This will be a head with LOTS of ventilation, almost completely open like it is now.
-
I'm confused by the voltages I'm reading on my PT secondaries with nothing connected to them:
Yellow - 214 V (specs say 5 V)
Yellow - 216 V
Green - 303 V (specs say 6.3 V)
Green - 299 V
Blue - 231 V (specs say 50 V - bias)
Red/Yellow - 186 V (CT)
Red - 113 V (specs say 660 V)
Red - 491 V
I know the voltages should read higher than the specs because the PT is unloaded but I didn't expect this big of a difference. Is this normal?
These readings were taken with just the main power, fuse, power switch and transformer primaries connected. I have Neutral going to the fuse which goes to the black PT primary lead. Hot from the wall is going to one terminal of the power switch, PT white primary lead to the other terminal. Ground connected to a ring terminal bolted to chassis ground. My meter was set to 700 VAC and I had the black lead connected to the chassis, red lead to each secondary - one at a time. Here is a link to the transformer I'm using: http://store.triodestore.com/deretrvipotr.html
-
All those readings are bogus because you don't have any secondaries connected to chassis. You must connect your voltmeter ACROSS the windings for the correct voltage.
Yellow to yellow will read 5vac.
Green to green will read 6.3vac.
Red/yellow to either red will read 330vac.
Red/yellow to blue will read 50vac.
Red to red will read 660vac.
-
Ah, across the windings, not to ground - duh!
So now I get:
Yellow to Yellow - 5.65vac
Green to Green - 7.06vac
Red/Yellow to Blue - 53vac
Red/Yellow to Red - 364vac
Red to Red - 730vac
-
Everything is assembled and wired. The amp doesn't work. :sad:
Here are my voltages. I think these are close to normal based on some others I compared them to on the Valve Data Page.
V1 - 12ax7
Pin 1: 247
Pin 2: 0
Pin 3: 2.02
Pin 6: 241
Pin 7: 0
Pin 8: 2.09
V2 - ECC81 (12at7)
Pin 1: 225
Pin 2: 65
Pin 3: 100
Pin 6: 230
Pin 7: 67
Pin 8: 100
V3 - 6V6s
Pin 3: 489
Pin 4: 488
Pin 5: -59
Pin 8: 0
V4 - 6V6s
Pin 3: 489
Pin 4: 488
Pin 5: -59
Pin 8: 0
I think I may have wired my input and output jacks wrong or the jacks I'm using are no good. They are switching jacks but looking closely at them it seems like they are not actually shorting when no plug is inserted.
With a guitar plugged into either input and a speaker connected to my main "Speaker" output I got no sound. Not even a little hum or buzz. Volume control had no effect.
With guitar plugged into "Hi" input and speaker connected to "Ext. Speaker" output I got no guitar sound but I did get hum/buzz. Volume control increased noise.
With guitar plugged into "Lo" input and speaker connected to "Ext. Speaker" output I got guitar sound but not good. Sounded like I was using an octave pedal (guitar signal plus an octave or 2 below). Lots of noise.
Please have a look at my jack wiring and let me know if anything looks wrong. I feel like I'm very close but I'm also very lost at the moment.
-
.
-
Those jacks don't look like Switchcraft so the lugs may be arranged differently from Switchcraft lugs. You'll need to verify which lug is which on those particular jacks.
If your speaker jacks are wired properly, you can't get any sound from the EXT. SPKR jack unles you have a plug in the main SPKR jack because the switch on the main jack will have the OT shorted out.
You can test the input jacks with your ohm meter and a guitar cord. Connect one meter lead to V1 pin 2 and leave it there.
1. With nothing plugged into either input you should read 34KΩ from V1-2 to chassis.
2. Plug your cord into the Hi jack. You should read 34KΩ from V1-2 to the free end tip of your guitar cord plug and you should read 1MΩ from V1-2 to the sleeve of the guitar plug.
3. Plug your cord into the Lo jack. You should read 68KΩ from V1-2 to the free end tip of your guitar cord plug and you should read 68KΩ from V1-2 to the sleeve of the guitar plug.
Here are some pics that may help. Your layout looks good for the jacks and if you had Switchcraft jacks wired IAW your layout they would be right.
(http://www.el34world.com/charts/images/jackwire2.jpg)
-
Oh, I forgot to mention... The tips of those speaker jacks 'appear' to be dangerously close to those screen resistors. Hopefully there's plenty of clearance. If the jacks come in contact with the leads on those resistors your speaker will blow almost immediately and the OT secondary will follow close behind.
-
Thanks Sluckey. These jacks are not wired like the Switchcraft jacks. That must be my problem - I didn't realize that, I just followed the diagrams you listed but these jacks have the switch and tip reversed compared to the Switchcrafts.
1. With nothing plugged into either input you should read 34KΩ from V1-2 to chassis.
I have 1.068M ohms.
2. Plug your cord into the Hi jack. You should read 34KΩ from V1-2 to the free end tip of your guitar cord plug and you should read 1MΩ from V1-2 to the sleeve of the guitar plug.
I have 1.068M ohms & 1.068M ohms
3. Plug your cord into the Lo jack. You should read 68KΩ from V1-2 to the free end tip of your guitar cord plug and you should read 68KΩ from V1-2 to the sleeve of the guitar plug.
I have 70.8K ohms & 734K ohms
I plan on swapping these jacks out with some I got at Radio Shack. They seem sturdier and the switch makes better contact with the tip than the ones I'm using now. The Radio Shack ones also have the switch and tip opposite from the Switchcrafts - interesting.
Thanks for the warning on the output jack tips being too close to the screen resistors. They are very close and I was a little worried but it doesn't look like they could make contact. Still, I'll see if I can rearrange that or at least insulate the resistor leads.
I hope I didn't damage anything by running the amp with all the jacks wired wrong. There was no smoke and nothing seemed excessively hot, in fact the transformers didn't even seem warm. I did get kind of a spark inside my V4 when I switched the Blue & Brown OT leads but when I put them back everything seemed normal. I have plenty of 6V6's though so if I ruined a tube, oh well.
-
With Sluckey's help I got my input and output jacks connected properly and now the amp works. I think it even sounds good but it's hard to hear the tone over all the hum and buzz. I think my bass and treble controls are a little weird too but that is the least of my worries at the moment.
I did a little chopsticking and didn't find anything. I'm worried the noise is from the orientation of my transformers. I hope not because there might not be much I can do about that short of doing a complete rebuild.
I'm open to any suggestions as to how I can figure out the cause of the noise and what I can do about it. The amp is not usable like this.
-
I've gotten absolutely nowhere with trying to determine the cause of this noise.
I've tried moving wires while the amp is running, jumping filter capacitors with others of equal or greater value, jumping ground wires to other ground points, swapping all the tubes, plugging the amp in in other locations/outlets, and probably some other things I can't remember. I even tried moving the OT but I was only able to remove one mounting screw and rotate it a few degrees - to move it any more I'd need to remove my board and disconnect a lot of stuff.
None of this has even altered this constant hum/buzz. My voltages are fine and bias is good. I have a very closely matched set of output tubes in now, within 1.5mA of each other.
The only thing left that I can think of is to run the filaments off of a 6V lantern battery, which I will try tomorrow I guess. Can the AC filament winding cause a loud, constant noise like this that doesn't change when the wires are moved?
I'm thinking of making a video with good audio quality to post on YouTube so maybe you guys can see/hear what I am and give some ideas.
What makes this even more frustrating is that behind all the noise I think I can hear the sound I was after when I started this project.
-
I just needed a virtual center tap for my filament winding with (2) 100 ohm resistors to ground. Somehow I missed that lesson in all my research. I don't think I'll forget it in the future.
I read about this before but I misunderstood the purpose. I thought it was for providing filament voltage for a PT that doesn't have it, not for grounding an existing filament winding. I shouldn't have missed it though, it's on the schematic.
This means I only made 2 mistakes in the whole build:
1) Not noticing the jacks I'm using have a different pinout than the Switchcrafts Fender used.
2) Not knowing about grounding the filament winding.
The amp is now much quieter than my Pro Jr. and gets the louder, spongy clean sound I was after.
There might be some tweaking to do but now my focus is on finding the right speaker for it. I think I blew or almost blew the 25W speaker I've been testing it with.
Thanks to everyone here for all the help and to Doug for maintaining this site and all the information it contains. There's no way I could have done this without it.
-
samoto,
Thats great to hear! I hope you have a lot of playin through it. :wink:
Brad :smiley:
-
Pictures of the finished product or you're lying!....Just kidding! :grin:
- Good job on getting it working to your satisfaction.
-
Pictures will come soon. I'll post them in the new gallery section and post a link here I guess.
It won't be a work of art like a lot of what I see here. That was never my goal and I don't think I'm capable of that. I'm working on a top to enclose my chassis/head and a speaker cabinet I'm building from scratch. Neither will be pretty but hopefully they'll work well and be durable.
On another note, I like the sound of this amp but I haven't really heard it properly yet. I'm running it through an Eminence Rajin Cajun 10" until I make my cabinet for a 12". One thing I notice is I think I prefer the extra grit provided on the Vibrato channel on a real Deluxe Reverb. I can't expect my amp to have that since I don't have those extra gain stages and added components. I think it answers my question about how much that stuff adds to the character of the amp (a lot). It's not really about more or less gain, it's just more something - mojo, character, grit?
I might look into building a stand alone outboard unit for reverb and tremolo. If so I'd like to make it as close to the Deluxe Reverb circuit but I don't know the first thing about how that works or how I would connect my amp to it yet. Can anybody point me in the right direction for some info on this?