# Fender Super Reverb AB763 Build



## Lincoln (Jun 2, 2008)

Well folks, here we go again. A Super Reverb this time, AB763 circuit, following a print by "RobRobinette". 

Little different grounding scheme from what good old Leo did. No brass plate, and the entire pre-amp section is grounded at the first channel input jacks. I'd like to hear some opinions on that way of grounding if I could. (please & thank you) 








Big iron, this thing is going to weigh just as much as a twin! (almost)








The face plate isn't as messed up as it looks in the pictures. It's new and still has the plastic film on it.


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## WCGill (Mar 27, 2009)

Nice Lincoln, ambitious project. Grounding can be tricky with this amp, esp. the reverb circuit. My experience only, and that with my own layouts. YMMV. Good luck, you've got the chops!


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## Lincoln (Jun 2, 2008)

WCGill said:


> Nice Lincoln, ambitious project. Grounding can be tricky with this amp, esp. the reverb circuit. My experience only, and that with my own layouts. YMMV. Good luck, you've got the chops!


Thanks WC
He's got the reverb transformer grounded to the chassis at the RCA jack for the reverb pedal. Not something I'd normally do. I've been grounding everything to the brass plate.

Maybe I should just stick to "as built by Fender" and forget about all those new-fangled ideas?


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## Latole (Aug 11, 2020)

Sometime is more easy to run wires to a brass plate like Leo did or solder a rigid wire all along the pot housing ( or apart and use it as a ground


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## Jimmy_D (Jul 4, 2009)

I used Rob's grounding scheme for a Bassman, Jtm45 and a Super Reverb... all were dead quite. They make sense to me but of course there many ways to do it so ymmv


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## Lincoln (Jun 2, 2008)

Jimmy_D said:


> I used Rob's grounding scheme for a Bassman, Jtm45 and a Super Reverb... all were dead quite. They make sense to me but of course there many ways to do it so ymmv


well that's good to know. I really do want to try something new and hopefully better.


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## Lincoln (Jun 2, 2008)

26 days later, after waiting for a new chassis to come in, we are starting over. A job worth doing, is worth doing right.

New chassis getting decked out with tube sockets and grommets 








And new iron as well








with F&T caps on the filter board. 
I'll be following Rob Robinette's layout to the letter. We'll see how it works out.


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## Hammerhands (Dec 19, 2016)

Why did you start over?


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## Lincoln (Jun 2, 2008)

Hammerhands said:


> Why did you start over?


well.....
I wanted this build to be way more faithful to the original amp than it was turning out to be. 

The chassis I had was either a custom build or had been modified in the past. It couldn't be used with the super reverb power transformer without a fill-in plate, and that would have looked like shite. I got that chassis on ebay, very many years ago and never used it. I was surprized when I discovered it wasn't everything I thought it was.

I had a transformer that fit the hole (twin reverb size) but it was designed for solid state rectification, and had other differences as well. It just kept snowballing on me. Abandon ship. I still have the amp I started with, and I will be finishing it sometime in the future.


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## Paul Running (Apr 12, 2020)

Lincoln said:


> It just kept snowballing on me. Abandon ship.


I know that feeling. It is amazing what a break will do from it. Your amp caddy looks very practical...keep-up the fine work.


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## Lincoln (Jun 2, 2008)

the flip side


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## Lincoln (Jun 2, 2008)

Paul Running said:


> I know that feeling. It is amazing what a break will do from it. Your amp caddy looks very practical...keep-up the fine work.


Thanks Paul. It was the Twin Reverb rebuild that finally broke me. Before that I was happy to man-handle amps on a table top, but the twin was too big and heavy to work on without fear of loosing body parts. About then, MojoTone gave Uncle Doug an amp caddy, the light in my head went on and built one loosely based on his.


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## Jimmy_D (Jul 4, 2009)

Looks very nice work, Rob’s layout has worked well for a lot of guys, I’m going to check in when you’re done to see what your experience has been, GLW the build and pls keep us updated


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## Lincoln (Jun 2, 2008)

Here's what the end of day 2 looks like









I find I'm really liking the extra-wide chassis of the Super Reverb. I think it's about an inch wider than the Deluxe or Princeton (medium size chassis), and that little bit extra gives everything room to fall into place.


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## Paul Running (Apr 12, 2020)

Looks like a very nice amp to work on...lots of hand and fingers room and that angle looks very comfortable.


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## Latole (Aug 11, 2020)

That are all Fender vintage amps or copy, easy to work on


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## Lincoln (Jun 2, 2008)

Progress report. I started on the power side and I'm working my way across to the pre-amp side. 








Rob Robinette threw a curve ball at me. He uses a DTSP toggle switch for the power on/off and runs both the white and the black primary wires through it. I've got one coming. I know I didn't need to do it, but it gives a good secure place to land the white wire, so I'll play along. That's a hum balance pot where the ground switch used to go. I use a lot of those now.


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## greco (Jul 15, 2007)

Lincoln said:


> Progress report. I started on the power side and I'm working my way across to the pre-amp side.


Thanks for taking the time to do the progress reports and for posting all these great pics! Much appreciated.
As always, beautiful work!


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## Latole (Aug 11, 2020)

Be careful with the wire dress. Don't do with other tubes what I see on PI tube.

1- Wires should not run close parallel.
2- They must run close to the chassis.
3- Wires that cross each other must do so at 90 degrees.
4- Wires must be short as they can.

Not following these recommendations will result in a noisy and/or wobbly amp.
That's Leo Fender and good amp builder work.

But if it's not the first amp you've built, you know all this

Look a this pictures


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## Lincoln (Jun 2, 2008)

little update, mostly control side


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## Latole (Aug 11, 2020)

Great job Lincoln,

Jjust one thing, I'll remove yellow tie-rap; most wire must not run close in parallel. They can induce noise.


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## Lincoln (Jun 2, 2008)

Latole said:


> Great job Lincoln,
> 
> Jjust one thing, I'll remove yellow tie-rap; most wire must not run close in parallel. They can induce noise.


first amp I've used a lot of tie wraps on. Just trying to make pretty. I could lose them, wouldn't hurt my feelings any.


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## epis (Feb 25, 2012)

Lincoln said:


> first amp I've used a lot of tie wraps on. Just trying to make pretty. I could lose them, wouldn't hurt my feelings any.


Just leave it, looks nice and tidy, no problem with noise in output/power stage.


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## Lincoln (Jun 2, 2008)

funny question of the day:

Do I want to pull the one power tube socket to get the on/off toggle switch into place? 

I can wiggle in a SPST switch no problem, but the DPST is a fair amount larger in the body.


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## keto (May 23, 2006)

Lincoln said:


> funny question of the day:
> 
> Do I want to pull the one power tube socket to get the on/off toggle switch into place?
> 
> I can wiggle in a SPST switch no problem, but the DPST is a fair amount larger in the body.


Gotta, right? Been there, at least variants therof. Occasionally, instructions interpretation related. Doh!


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## Lincoln (Jun 2, 2008)

I guess it's update time.

I had to give up on the running both white & black primary wires through a DPST toggle switch. It will not fit as the toggle switch hole lines up perfectly with a power tube socket. Not enough room.
All the wiring finished now, ready for testing.


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## Lincoln (Jun 2, 2008)

Almost everything went well with testing last night. I managed to touch a terminal with B+ and ground at the same time with voltmeter probe. It makes a very loud "snap". The wife heard it half a house away.


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## jb welder (Sep 14, 2010)

Lincoln said:


> I managed to touch a terminal with B+ and ground at the same time with voltmeter probe. It makes a very loud "snap".


Is your last name Welder? Are we related?


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## Lincoln (Jun 2, 2008)

jb welder said:


> Is your last name Welder? Are we related?


Could be. There wasn't much welding going on, but I sure discharged the filter caps in a hurry! Now I know for sure why a resistor is used to discharge caps.


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## Paul Running (Apr 12, 2020)

There is a great deal of potential energy in a fully charged, HV cap...an example (verification of the math would be appreciated):
The energy in Joules, stored in a 40µfd cap charged to 450V can be calculated as:
= ½ (.00004F)(450V×450V)
= 4.05Ϳ
where C is capacity in Farads and U is voltage differential.

In theory, if this energy is dissipated within 10µsec the potential power generated can be calculated as:
P = 4.05 Joules / 10×10-6 sec
= 405KW
A very short duty cycle however, a great deal of energy.


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## Lincoln (Jun 2, 2008)

Paul Running said:


> There is a great deal of potential energy in a fully charged, HV cap...an example (verification of the math would be appreciated):
> The energy in Joules, stored in a 40µfd cap charged to 450V can be calculated as:
> = ½ (.00004F)(450V×450V)
> = 4.05Ϳ
> ...


The energy dissipated so fast. it didn't even have time to heat up and destroy the probe of the volt meter. But I'll never forget that sound. The sound of instant respect.


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## Lincoln (Jun 2, 2008)

A little issue I've been playing with on this build, hoping one of you can point me in the right direction.

The tube bias circuit. My bias voltage has a range of -49V to -70 volts, which in my experience should be right on the money. However, measuring at the 1 ohm resistor between ground & cathode, I can only get .019 volts max. I know it must have something to do with it being negative voltage, and that's what is causing my thinking to go sideways. I've double checked all the resistor values, and they are correct. 

Writing this out has help me realize I need less negative voltage to get to where I want to be. I need to increase the resistor on the bias board, correct?


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## Lincoln (Jun 2, 2008)

Problem solved, thanks guys 

I increased the value of the resistor on the bias board, and decreased the value of the resistor on the bias pot to ground. Now I have all the range of bias adjustment a man could ever ask for. The bias pot resistor made the most drastic change. The Rob Robin layout I was following asked for a 27K on the bias pot. Fender asks for 10K, and changing to 10K did the trick.


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## Paul Running (Apr 12, 2020)

Lincoln said:


> I can only get .019 volts max.


Your observation matches the characteristic curve for the 6L6-GC; on the graph below, note that the plate current is about 20mA (20mV across a 1Ω resistor), with -50VDC on the control grid. -70VDC is well into cut-off.


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## l.a.solis (Feb 1, 2021)

Sweet


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## Lincoln (Jun 2, 2008)

And Speaking of winter projects in the other thread.........reminded me of a project I didn't finished last march. Close but no cigar. Sitting in the shop, collecting dust. 










Front panel was made, just needs grill cloth.


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## Lincoln (Jun 2, 2008)

This amp did finally make it to completion btw


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## greco (Jul 15, 2007)

Lincoln said:


> This amp did finally make it to completion btw
> 
> View attachment 392444


CONGRATS! Looks beautiful!

The perfect Super Reverb IMO.
Lots of possible choices of speaker cab configurations.
Does the OT have three impedance taps?


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## Lincoln (Jun 2, 2008)

greco said:


> CONGRATS! Looks beautiful!
> 
> The perfect Super Reverb IMO.
> Lots of possible choices of speaker cab configurations.
> Does the OT have three impedance taps?


Thank you 

It's been a while, so I had to go look, but I always use multi-tap OT's. For the little extra money, I feel they are well worth it. 

This one is set up for either 4 ohm or 8 ohms. The wire for 16 ohm is tucked away inside should it be needed. Thank you for reminding me to label the 4/8 ohm jacks.


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## Lincoln (Jun 2, 2008)

a back shot or three:










external bias ports










and a "hum-pot" where the ground switch used to go


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