Tube Amps / Music Electronics
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|9/14/2000 5:23 PM|
|Bob P||HELP! Hummmmmmmmmm|
I have just converted a reissue Bassman. The Circuit board was replaced with all new components (Sprague caps, 1/2 watt CC resistors, etc) and wired point-to-point. The caps in the power section were moved over to make room for the 20/500 cap that was on the board. The amp works except for a loud 120 cycle hum.
Suspecting the power caps I checked them all and found no obvious problems. I strapped each one, in turn, with a new cap with no improvement.
If I pull V1 the hum stops.
With V1 in, if I remove the wires from the input jacks, the hum is reduced, but is still very much there.
With the volume controls up, I also have A) motorboating and B) a low volume but high frequency squeal like air being slowly let out of a balloon.
Lead dress is as short as it can be.
Also, the hum varies with the movement of the volume controls and the tone is shaped by the tone controls. If the volume controls are all the way down, the hum stops.