Peavey AlphaB , what's the deal with ?

[catalin gramada]

Heaters supply solved as it was just a matter of wiring. Also all capacitors in power supply was replaced with new ones.
Anything works as it should, voltages seems in range, still the amp in not completly quiet, it have a slight hum. Any thoughts about a good start to track it please ?

[catalin gramada]

Schematic here
AlphaBass - Bass Head Amp.pdf

[Enzo]

There are endless sources of hum in an amp. You have to track down the source, then we can determine what to do about it.

[catalin gramada]

There are endless sources of hum in an amp. You have to track down the source, then we can determine what to do about it.

Thanks Enzo. The hum was here from beginning. I hoped changing the filter caps get rid of it but this was not happened.

[catalin gramada]

The hum balance pot do almost nothing, is very subtle. I drawled the circuit below:

[Helmholtz]

50Hz or 100Hz?

[catalin gramada]

Didn't scoped nothing yet my bench is in garage and is too cold to work over there. I tried to fix it in the kitchen when my wife don't cook...

[glebert]

For hum I approach it the same way I do any issue, divide and conquer. Does it go up and down with master volume? If so it is in the preamp, if not it is later. Can you short out the signal at various points to isolate? If I want to short out a node that has DC voltage I will solder in a large cap to ground, etc.

[catalin gramada]

Thanks. It seems is from first stage.