Converting a Twin Reverb re-issue into a point to point circuit board.

[rockman627]

First of all, I've read a few posts here and there saying there is no need for this conversion. In this particular case there is : the amp has revolving and recurrent problems. It was purchased from Toots and the Maytals and sat in a hot humid environment for months prior to that. The notes said "bad tubes and no reverb" , so I replaced the tubes and started examining the reverb circuit.

At this point I will say I work for a backline rental company maintaining guitars and amps when I am not filling orders. So, I have access to extra amps, some parts etc. Also the company does not provide a computer so I have to go home to post and forget some details by the time I get home.

I was able to put the suspect reverb tank in another Twin and confirm it was ok. I plugged a guitar into the reverb return and confirmed that circuit was OK. The reverb driver did not test OK. I should mention the send and return jacks were separated from the board and it didn't look like it was jumpered correctly by my predecessor. I rebuilt the driver circuit as per the schematic and I got signal to the reverb tank, but it was noisy and trebly. I traced the circuit again and found no connectivity between 2 points that should have connected. Now it sounds OK. But when I put the twin back together, no reverb. I take it back out, check through the driver and return circuits again: tests OK. Reverb starts working again, but noisy and trebly. I put it aside to work on other amps. When I got back to it, there is no sound at all.

My co worker said my predecessor experienced the same thing and the amp became known as the Bermuda Triangle amp. I want to recommend to my boss to let me rebuild the circuit on a turret board. I would also want to replace the pots to get rid of that circuit board. To keep the costs down, I would like to keep the transformers.

So, here is my question: does the reissue transformer connections correspond to the original AB763 connections. Will it be just follow the schematic or will modifications be necessary?

[nevetslab]

First of all, I've read a few posts here and there saying there is no need for this conversion. In this particular case there is : the amp has revolving and recurrent problems. It was purchased from Toots and the Maytals and sat in a hot humid environment for months prior to that. The notes said "bad tubes and no reverb" , so I replaced the tubes and started examining the reverb circuit.

At this point I will say I work for a backline rental company maintaining guitars and amps when I am not filling orders. So, I have access to extra amps, some parts etc. Also the company does not provide a computer so I have to go home to post and forget some details by the time I get home.

I was able to put the suspect reverb tank in another Twin and confirm it was ok. I plugged a guitar into the reverb return and confirmed that circuit was OK. The reverb driver did not test OK. I should mention the send and return jacks were separated from the board and it didn't look like it was jumpered correctly by my predecessor. I rebuilt the driver circuit as per the schematic and I got signal to the reverb tank, but it was noisy and trebly. I traced the circuit again and found no connectivity between 2 points that should have connected. Now it sounds OK. But when I put the twin back together, no reverb. I take it back out, check through the driver and return circuits again: tests OK. Reverb starts working again, but noisy and trebly. I put it aside to work on other amps. When I got back to it, there is no sound at all.

My co worker said my predecessor experienced the same thing and the amp became known as the Bermuda Triangle amp. I want to recommend to my boss to let me rebuild the circuit on a turret board. I would also want to replace the pots to get rid of that circuit board. To keep the costs down, I would like to keep the transformers.

So, here is my question: does the reissue transformer connections correspond to the original AB763 connections. Will it be just follow the schematic or will modifications be necessary?

Welcome to the Forum! This is a pretty adventuresome project you're contemplating. We've seen numerous Fender amps rebuilt, scraping their PCB boards as well as scraping the tag board versions as used in the AB763 release. So, with some homework, there are some excellent posts to use for ideas and techniques. If your wiring skills are up to it, and you have the time & space, I'd say go for it.

Regarding the power xfmr, the two obvious differences between your reissue xfmr and the one in the AB763 is you don't have a CT on your high voltage winding, the bias circuit has it's own winding, and the heater winding has a centertap. Easy enough to discretely wire the new power supply to accomodate your existing power xfmr. I prefer having a hum balance pot, though I've replaced a lot of the low-wattage 100 ohm pot Fender uses. Good enough to reuse until it eventually fails, if ever.

So your plans with regards to the front panel controls...scrap that PCB and replace or make use of the pots? The AB763 uses 3/8" bushings/1/4" shafts, with solder lugs, which do make it easier to add the tone circuit caps, but no reason why you can't do that with the pots from the PCB. At least with the pot terminals face up, you can get at the resistance track/wiper for applying contact cleaner without having to pull the bloody PCB assembly out. And a major plus.....you get to scrap those HORRIBLE pcb phone jacks!! Switchcraft 12A T/S with normals.....last forever!

You do have an odd ailment with the Reverb Send circuit as you describe.

From a maintenance standpoint, its a whole lot easier servicing the earlier amps with tag board, assuming you don't have long term moisture absorption issues that you will / have read about here. On the Turret boards, depending on your wiring technique, wrapping leads around the turret posts, and wiring the circuit both above and below the board does make for a nice layout, though having to unsolder and unwrap wires from terminals makes me nuts when having to change out parts. I learned point to point wiring from all of the tube-based Tektronix scopes and their plug-ins, and they built incredibly solid units laying their component leads into those nice sliver-solder filled ceramic strips as well as tack-soldering components in series flying between anchored ends. All about proper solder technique.

[nosaj]

First of all, I've read a few posts here and there saying there is no need for this conversion. In this particular case there is : the amp has revolving and recurrent problems. It was purchased from Toots and the Maytals and sat in a hot humid environment for months prior to that. The notes said "bad tubes and no reverb" , so I replaced the tubes and started examining the reverb circuit.

At this point I will say I work for a backline rental company maintaining guitars and amps when I am not filling orders. So, I have access to extra amps, some parts etc. Also the company does not provide a computer so I have to go home to post and forget some details by the time I get home.

I was able to put the suspect reverb tank in another Twin and confirm it was ok. I plugged a guitar into the reverb return and confirmed that circuit was OK. The reverb driver did not test OK. I should mention the send and return jacks were separated from the board and it didn't look like it was jumpered correctly by my predecessor. I rebuilt the driver circuit as per the schematic and I got signal to the reverb tank, but it was noisy and trebly. I traced the circuit again and found no connectivity between 2 points that should have connected. Now it sounds OK. But when I put the twin back together, no reverb. I take it back out, check through the driver and return circuits again: tests OK. Reverb starts working again, but noisy and trebly. I put it aside to work on other amps. When I got back to it, there is no sound at all.

My co worker said my predecessor experienced the same thing and the amp became known as the Bermuda Triangle amp. I want to recommend to my boss to let me rebuild the circuit on a turret board. I would also want to replace the pots to get rid of that circuit board. To keep the costs down, I would like to keep the transformers.

So, here is my question: does the reissue transformer connections correspond to the original AB763 connections. Will it be just follow the schematic or will modifications be necessary?

From a business standpoint you have a really hard sell in front of you. a $1500 amp to rewire(what 10 working hours ) plus parts. That better be one money making amp.

Most important question is how old is the amp?

You know they do have a warranty.

nosaj

[nevetslab]

From a business standpoint you have a really hard sell in front of you. a $1500 amp to rewire(what 10 working hours ) plus parts. That better be one money making amp.

Most important question is how old is the amp?

You know they do have a warranty.

nosaj

I'm thinking maybe your boss would let you do it if you're providing all the labor for free, or a couple hundred bucks. I know I can't rebuild one of these from scratch in 10 hrs. 40hrs maybe, after dealing with all the unforeseen tedious steps in the way, as well as troubleshooting it when it doesn't work right off. If it's not being done as a labor of love, I agree with nosaj.

[nosaj]

I'm thinking maybe your boss would let you do it if you're providing all the labor for free, or a couple hundred bucks. I know I can't rebuild one of these from scratch in 10 hrs. 40hrs maybe, after dealing with all the unforeseen tedious steps in the way, as well as troubleshooting it when it doesn't work right off. It it's not being done as a labor of love, I agree with nosaj.

10hrs was just off the wall but figure 10hrs at what 10/hr thats a 1000 right there in just labor. I'd think maybe you have a parts donor there from a business perspective.
Businesses don't often have labors of love.
nosaj

[Justin Thomas]

10hrs was just off the wall but figure 10hrs at what 10/hr thats a 1000 right there...

Wait, whut? Either you're WAY under regular market labor price or bad enough at math that I could take advantage. Either way, I'll go with YOU! That's almost bette. than doing it myself!

Just ragging you - I know you meant $100/hour. I think. Seems a lot more in line if you're in the right place. Anyway, carry on.

More seriously, I'm sure there are turret boards already made for these. That saves a lot of labor right there. Wiring & soldering is the easy part in my opinion... Laying crap out & drilling holes & staking turrets? Not so much.

Jusrin & Justin

[nosaj]

Wait, whut? Either you're WAY under regular market labor price or bad enough at math that I could take advantage. Either way, I'll go with YOU! That's almost bette. than doing it myself!

Just ragging you - I know you meant $100/hour. I think. Seems a lot more in line if you're in the right place. Anyway, carry on.

More seriously, I'm sure there are turret boards already made for these. That saves a lot of labor right there. Wiring & soldering is the easy part in my opinion... Laying crap out & drilling holes & staking turrets? Not so much.

Jusrin & Justin

Yea not good with math or tape measures which is I paint at the cabinet shop instead of building

Major point being the only way the conversion would happen is if this guy owned the amp(buy it from owner) or if the shop wants to throw away money .

Before anything is done if it's less than 2 years I'd check factory warranty.

nosaj

[Justin Thomas]

Heck, if I averaged out what I charge for an amp versus labor I'm charging less than sweatshop rates... But I also have no proper shop or scope & I build true PTP & mo two are ever alike, so most of that time is chasing noise anyway. Don't feel like I should charge for that!

Justin

[nosaj]

Heck, if I averaged out what I charge for an amp versus labor I'm charging less than sweatshop rates... But I also have no proper shop or scope & I build true PTP & mo two are ever alike, so most of that time is chasing noise anyway. Don't feel like I should charge for that!

Justin

yes the true p2p may look messy , but I think the same as looking at art. If you don't know what your looking at you can't appreciate the artform. Man some of the 40's RCA amps were awesome. I had one that for a bussbar looked like 12guage wire in wove between the sockets.
nosaj

[The Dude]

Those amps are notorious for crappy solder connections. I think before I rebuilt the thing, I'd get out the iron and resolder the entire board(s). It really doesn't take that long. Check solder on sockets also.

[Bill Moore]

My first build was a AB763 Twin. I built the turret board, and picked the parts as I wanted, after all it was for me. I don't think anyone with some electronic knowledge will have any problem doing a conversion, but I'm not sure it's cost effective in the enviroment the poster states.
Has anyone bought any of the circuit boards "pulls"? They are seen on the 'bay once in a while fairly cheap, are they pulls from problem amps?

[Leo_Gnardo]

Has anyone bought any of the circuit boards "pulls"? They are seen on the 'bay once in a while fairly cheap, are they pulls from problem amps?

One never knows... But there are occasionally musos who opt to have their pcb "reissue" amps fitted with PTP boards, then sell off the pcb to recoup some of the build cost. Or the tech sells it for a beer money bonus.

Rockman, I'd check with Doug Hoffman about pricing on a pre built PTP board for that Twin, loaded with good parts and including pots. I did a number of RI '59 Bassmen and 50W Marshalls in the mid 90's with his boards. Sure saves the hassle of building your own from scratch.