Silverface Fender Twin Reverb rebuild

[kristianf]

Hi all!

I recently acquired a silverface Fender Twin Reverb. I bought the amp in non-functioning condition, in part of a backline clearance.
The reason i bought the amp was because of the JBL D120F speakers, to pair with my silverface Bassman for pedalsteel use.
I got a pretty good deal on this Twin, and I already knew that it hasn't functioned properly for 15 years or so.
Due to that, I decided to pull the chassis and take a proper visual inspection before firing the amp up.

I have to admit that i was pretty shocked by what I saw. The amp had tells of previous modifications, as it has four different fuse holders on the back panel. The stock turret board and it's components looks mostly original, as far as I can tell, but the work done to it later is hazardous and pretty much the worst I've ever seen. Absolutely mind boggling that what I assume is a professional technician can do such terrible work.
The power tube sockets and components looks pretty damn shitty, and the more I poke around inside of this amp, the less faith I have in it's current condition. There are a lot of damaged insulation and wiring.
There's a lot of dodgy solderjoints all over the place. The unused taps of the export power transformer has been disconnected from the original rotary switch and was just bundled in one piece of electrical tape, no separate heat shrinking or anything. These are leads are cut very short, but I hope that I can manage to blind the unused taps in a safe fashion. Would these short tap leads pose any noise related/proximity issues in this way?

I don't have a lot of experience working on amps outside of bias adjustments and normal routine stuff, but I am an maritime electrician by trade and already have good soldering skills, so I have considered getting into the DIY amp building for a long time. I have been studying amps for the last while and think that I'm ready to begin DIY'ing the coming months.
After looking inside of this amp, I think the best solution would be to gut it, re-use the transformers and build something like a Hoffman single channel AB763, probably without reverb and tremolo.
The filter capacitors are the originals from the 70s, so it would have to be recapped anyway.
What do you guys think? Is it even worth trying to safe an amp in this condition or should I just gut the thing asap and start a DIY project?
I haven't had the time to measure the transformers to confirm that they are OK, but I will get to it shortly.
To be honest, I have a feeling that this amp will be a potential gold mine of trouble.

[xtian]

Welcome to TAG! Good job spotting the issues with this amp, but from the perspective of someone who's seen inside many Fenders, this one isn't looking bad at all. Some things need to be cleaned up, as you noticed, and the filter caps need replacing--but that's true of every vintage Fender with original caps. No big deal.

"Would these short tap leads pose any noise related/proximity issues in this way?" No, that's not an issue. But as you said, you want to make sure these wires don't short to each other.

Are the transformers good? If this amp plays at all, then yes. Why tear everything out and start from scratch? There's nothing here that can't be fixed in a few hours, and then you can evaluate how it plays.

[kristianf]

Thank you very much!
Upon further inspection, a lot of it looks better than i feared, though some thing will have to be repaired.
There are damages to the wires and components caused by the previous bad repairs, but I think it will be manageable.
As soon as I have the time, I will rewire the ins and outs from the PT, as there are a lot of damaged wiring there. I'll also have to rewire the heaters for the power tubes, as the insulation is damaged, and I think I'll touch up the grounding for the power tubes while I'm at it.
The leads from the powertubes to the OT have damaged insulation, so I'll have to take into consideration how to fix that in the least intrusive way.
I would much prefer to save as much of the original OT leads as possible, so I might save the fuse holders and use them for junctioning the power tubes and the OT.
I will start checking out the transformers asap!

[xtian]

Sounds good. You can use heat shrink tubing to re-insulate the PT leads.

While you're messing with the power tube grounds, you should add 1 ohm resistors from pins 1+8 to ground, to make checking bias simple.

[DimenBrun]

Did you ever get this twin working? Like xtian had stated this doesn't look that bad. The sloppy lead dress is standard CBS Fender assembly as I have seen many times. I had a twin back in the late 70's that I used in cover bands. To be honest, I never really liked it that much. It had the pull-master boost, which had a horrible sound. The cleans were TOO clean and sterile sounding. Adding an actual bias pot helps that, but it will be at ear damaging levels before getting much give out of it......if you get my meaning. The JBL's make it even louder than the other Fender speakers that came in some of these twins. I ended up modding the hell out of it, which in hindsight was probably not the smartest thing. A distortion pedal would have served me better, cheaper....................and retained the resale value better! Live and learn.

[kristianf]

Quite the delayed answer here. I've been busy with other stuff, and haven't had the time to do much to it.
I've only re-glued and fixed the combo cabinet and un-modded the wiring. Ripped out quite a bit and inspected it. All the heater wiring will have to be rewired.

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[dragonbat13]

Some of those fuse holders may be actuall protecting the transformers.

I have a twin that looks just as bad. CBS era wiring is horrendous. And the crap wire they used will melt if you breath on it too hard.

My plans with my twin are to use a hoffman board, and install individual bias for each tube. Also some different master volume. I really liked the MV on my twin. It's just too loud without. Also, I want to replace my board because it has conductive issues. And its noisy. Mines a 72, pre push pull mv. I want to regain as much of its silver face tone as I can. I dont want it to be a blackface twin, I want it to be a silver face twin. Whatever that means.