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Ground-like Hum, Increasing as amp warms up

mattjhuber

Member
Messages
118
Wanted to know if you guys could help me get to the bottom of an issue in my amp...

It is a Morgan TR19 (LOVE IT by the way). At any rate, it has recently been developing an issue...

When I power it up, everything is fine and dandy, but as it warms up, a ground-like hum slowly creeps in, and ends up being decently loud. I noticed that increasing the reverb will bring up the volume of this hum.

Any ideas? Figured I would check with you guys before bothering Joe about it...hoped maybe it was something simple.

Thanks!
 

TimmyP

Member
Messages
2,488
Duff filter cap, preamp tube that's coupling the heater supply into the signal, duff heater supply center tap.
 

Jeff Gehring

Gold Supporting Member
Messages
6,746
As was said by DDD, check the idle current for your 6V6's. If they drift off match appreciably, the hum level will increase since the balance of the push-pull pair is off. If they still are matched, then you'll need to look elsewhere, but that's what I'd check first.
 

ACETECH

Member
Messages
28
As tubes warm up it takes a while to reach maximum conduction. The first place to look is the High voltage filter caps, then preamp tubes, then the power tubes. You can isolate the power tubes by unplugging them.
Sometimes a preamp tube will cause that problem.
Good Luck
Paul
 

wyatt

Member
Messages
4,168
All good suggestions up top.

One other thing,...you might want to have someone double-check all the solder joints.
 






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