Twin Reverb Problems

[Gibsonman63]

I don't have the last week and a half of pictures posted yet. I pulled the bus bar and scrubbed behind it, polished it up and re-installed it. I had the amp playing on the normal channel before I replaced the pots, so either my cleaning effort or my soldering must be giving me grief, but I have the problem isolated enough to know that my voltage isn't getting past the diode board. I should have ordered a new bias pot when I ordered the other pots, but live and learn. I'll take your advise on the diode board as well. I think the wire may better than it looks. It is discolored, the insulation is not brittle.

Thanks for the help.

[Mars Amp Repair]

hello,
The first problem I see might be rejection from 'Gibsonman' working on a 'Fender' ;-]...ok all that sillyness aside,

I think as rusty as this amp is, I'd be certain that the ground lug for the secondaries on the power transformer that is ususally underneath one of the transformer mounting nuts, is clean & tight & actually making a good ground connection there.

Secondarily I'd just for certain given all the weirdness you're experiencing, replace that bias rectifier diode for sure. If there were a short after that diode, the 470ohm 1watt resistor on the diode board would for sure be getting reeeeeally hot, & it doesn't appear that is happening.

Also be certain that the ground point at the + of the bias filter capacitor is actually going to ground. No filtering, no clean DC reading at the bias point. If you don't have a scope, you could switch to the AC scale & see if you read more voltage at the - of the bias cap. If so, there's an issue there. I'd verify the ground at the cap as well as just replace that diode.

glen

[Gibsonman63]

Good point about cleaning up the grounding, I missed the one on the transformer lug, but will definitely clean that one up right away. I have redone all of the grounds to the bus bar already, but I haven't updated my photos. Is it worth while to redo all of the grounds that are soldered directly to the chassis?

[MWJB]

"Is it worth while to redo all of the grounds that are soldered directly to the chassis?" They should be OK. If you were to remake them it takes a hefty soldering iron to get the chassis hot enough.

[olddawg]

I have a 1960 Ampeg Jet that was pulled out of a trash heap. It looked about as bad. It is not as complex of an amp so fixing it was easier. It took some time and it is still ugly (I say it has character) but it works well enough now. The price was right (free) and I didn't repair it in one day. I tell you, if that Twin was my amp and I wanted it to be reliable, after I had the bandaide fix done and it was working, I would completely disasemble it, sand blast the chassis, clean all of the boards, replace all of the nuts and bolts and any other rusty hardware, and wire brush anything (like pots and such) I planned to reuse. There are places that can restore the faceplate or you can get a replica and re-tolexing the cab isn't that difficult. If you got it cheap enough, the transformers are good, and you have the time; the only thing to do is a complete restoration. Otherwise, it will plague you with wierd and frustrating problems. You might even consider selling it once it is restored and buy another.

[bob p]

<sigh>. I hope the board's new software upgrade will fix this kind of problem.