Quote:
Originally Posted by starcitysongs
Thanks for the suggestion. I gave that a shot today and it didn't remedy the problem. What are the possibilities of this being a bad OT in both amps? Is there a safe way to test an OT? Also anyone have any other suggestions?
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You can check for DC resistance when it is powered down/
You should read 40-100ohm on the primary winding,
.5 - 1.5 on the secondary,
and at least 10k ohm between the primary windings and both the secondary and the chassis.
This is just an indicator, it could pass these tests and still be faulty.
If you have either a variac of signal generator you could also (when powered down) inject about .5Vac signal into the secondary and check the voltage on the primary. Anything much outside the turns ratio you would expect or no signal will indicate a problem.
I think you should start checking the preamp tubes with known good ones. At the same time check their plate resistors for signs of damage and that they are reading correct values. If that fails to solve the problem it's time to start checking DC resistances on the pre-amp stage coupling caps. The problem does not appear to be with the power section from what you've said so it's not likley but double check the filter caps anyway for any signs of bubling and DC resistance to ground.
It's unlikley that the OT would be gone in both amps as it is rare enough to go in one amp assuming the correct HT fuse is installed. Also when they go, they go. They wouldn't normally work OK for a while and then go. I found a
5 amp in a amp recently and that was the first time I've seen a failed OT.