65 Twin Reverb Vibrato Problem. Please Help

[Bradley]

Howdy all. I am new here, but I thought I'd give it a try. Here's whats happening. At first I would step on the vibrato foot switch and it would work for 10 minutes or so then it would begin to quiet and then disappear. Now the vibrato Oscillates a couple of times and stops. I tested the bug with a flashlight and it seems to work. What I notice is that when the I step on the switch the neon flashes a couple or three times and then remains on. I am just getting into electronics so I'm not sure where to go next. I am perplexed. Any ideas?

[Chuck H]

The flash is in response to the oscillator triode. If you don't have oscillation you don't get trem. Have you tried a new tube?

Chuck

[Bradley]

I swapped out the tube with one from my blues jr., same tube of course, but to no avail. From some of the other threads I have read I am thinking that it could be the caps in the vibrato circuit. I appreciate the response. I will keep researching. Thanks to all for looking.

-Bradley

[Chuck H]

Check voltages on the tube. It could be the cathode or plate circuit keeping the oscillator from functioning. If voltages check out try cleaning the footswitch jack. If that doesn't work you could just shotgun the whole circuit with new caps, resistors and "roach".

Chuck

[Bradley]

Thanks Chuck, I'll try a voltage test when I get home tonight. As for the footswitch; I initially thought that was the problem so I took it apart and cleaned and resoldered all connections. I'll let you know where I end up after a voltage test. Thanks for pointing me in the right direction.
-Brad

[Enzo]

Your caps are 40 years old. I would replace the cathode bypass cap and the three feedback caps in the oscilator circuit. You could try searching for a bad cap in there, but really, those parts are cheap, just replace the whole set.

The amp may well be ready for new electrolytic caps throughout.