SWR 350 hum problem

[Axtman]

I am repairing a SWR "Red Face" 350 bass amp head. It has a hum on the output of the speakers that is about 35 volts at 12 Hz. The power transformer and filter capacitors test fine and put out about 62 volts plus and minus. Would a shorted output capacitor cause this problem?

Thanks!

[Enzo]

I don;t know that I can even hear 12Hz.

What output capacitor are we talking about? I don;t know of one.
Set your meter to AC volts and recheck those 62v rails. You should get very little AC volts. if you get substantial voltage - like 30v or something - then the filter is not doing its job.

Does plugging into the FX return or power amp in jack make a difference? DO ANY of the controls affect this sound in any way?

Disconect the speaker load, is the signal still on the output? use a scope or meter to find out.

is the signal input connected to the powr module? The ground connection in that cable is important to the stability of the amp.

[Axtman]

Oops! I meant output TRANSISTOR.

The hum sounds like 60 Hz but my multi-meter says it is 12 Hz.

I will check those items. Thanks!