Reverb shuts off when amp gets hot

[5thumbs]

I have a CBS build amp that is loosing the reverb when it gets hot. I have replaced the driver and recovery tubes, tried different RCA cables, tried a different reverb tank, nothing helped. Could it be a bad coupling cap or bad bias resistor or bypass cap? Any help to narrow it down would be great! I know you guys have probably seen similar things like this and it is an easy fix!

Thx,
Tim

[g1]

Try to narrow it down to the drive or recovery side of the circuit. When it cuts out, shake the tank. If you hear a crashing sound, then the recovery side is good and the problem is likely the drive circuit. If no crashing sound when shaken, the problem is probably the recovery side.
Also, the problem is not necessarily a bad part, it could be a bad solder joint or connection which is ok when cold but bad when heated up.

[J M Fahey]

Dear Tim, don't throw parts at it at random
Apply some known signal, say 100mV@1KHz to the reverb driver, trace and note it along the way, until where it rejoins the main amp, wait for it to dissappear, and recheck along the path to see where you lose it.
Then you are very close to the problem.
Which may very well not be "a part" at all, but a connection problem or something similar.
It's the shortest and safest path.
Good luck.