1975 Fender Twin 2nd channel distorting - Help!

[Whitey-on-the-moon]

I've recently purchased a silverface Twin - 100 Watt master volume. It's currently with my amp tech undergoing service as it has the following issues.

- Reverb crackling on and off.
- Same with the tremelo and very weak.
- The vibrato and tremelo channel is distorting.

It still had it's original valves in so they have been swapped out, the neon has been changed in the octocoupler which has improved the tremelo slightly and a new octocoupler has been ordered from Fender. He plans to fit the new octocoupler to see if it brings the tremelo back to it's former workings.

Main concerns are the the distorting of the 2nd channel. Has anyone here had experience with this fault and successfully fixed it?

Same with the reverb? I thought it may be the paper caps but the normal works fine. The amp has only been switched on a few times since about 1980. Any help is much appreciated. Thanks in advance!

[ahamay79]

Replace all the electrolytic caps. They are probably dried out, plus they're 34 years old.... they need replacing. Replacing them will correct many problems and allow you troubleshoot without chasing other possible problems.

[Whitey-on-the-moon]

Replace all the electrolytic caps. They are probably dried out, plus they're 34 years old.... they need replacing. Replacing them will correct many problems and allow you troubleshoot without chasing other possible problems.

Thanks I'll run this suggestion by my amp tech. If it were the electrolytic caps then wouldn't affect the normal channel also? The normal channel works fine.

[pdf64]

With respect, your tech is the guy with the amp in front of him and so best placed to resolve the issues. Everyone else is just shooting in the dark.
If he's anything like me, he'll cringe inside when you ask him if he's done this or that because you read something on the www.
Best to let him get on with it, nothing in there is rocket science.
If there's still issues which become apparant when you get it back, then we'll know it's an oddball problem which the usual service type stuff hasn't fixed properly, and we might be able to come up with something useful.
There are electrolytic caps throughout the amp. Peter.

[Whitey-on-the-moon]

With respect, your tech is the guy with the amp in front of him and so best placed to resolve the issues. Everyone else is just shooting in the dark.
If he's anything like me, he'll cringe inside when you ask him if he's done this or that because you read something on the www.
Best to let him get on with it, nothing in there is rocket science.
If there's still issues which become apparant when you get it back, then we'll know it's an oddball problem which the usual service type stuff hasn't fixed properly, and we might be able to come up with something useful.
There are electrolytic caps throughout the amp. Peter.

Fair comment and I fully agree. The reason I'm here is becuase he mentioned the distortion was something of particular concern and the cause not apparent. I just wanted to see if by pot luck if it was anything common with these amps that could easily be diagnosed. I'll wait and see the outcome from the service.

[tim]

One thing to remember on these amps that there is normally more signal distortion in the second channel than the first. That's why most people use the 1st channel for clean tones and the 2nd for grittier tones...

[ahamay79]

There are more electrolytics in the amp than just the filter caps (blocking caps, bias cap(s), etc. On an amp that old I always replace those old caps before I start trying to find other problems.

[Whitey-on-the-moon]

One thing to remember on these amps that there is normally more signal distortion in the second channel than the first. That's why most people use the 1st channel for clean tones and the 2nd for grittier tones...

It's not your standard gritty fender break up unfortunately. It comes in when the volume is on about 2 and these amps supposed to be sparkling clean.

[hollisdevillo]

yeah all those caps have a life of maybe 20 years, depending how much they're used. once that's all done, then see what's happening. as ahamay79 said the caps are throughout so a blocking cap between stages could be bad and throwing off the second channel distortion. it could be a number of things. thats why instead of troubleshooting each cap, it's far easier and less time consuming to just change them all, since they're in need of a change anyway. as gerald weber says, it's the "texas shotgun special." should also consider blackfacing it.