1980 Randall RB60 humming

[acorkos]

the volume and tone controls work, the amp sounds ok, except a relatively loud hum. tone controls affect the hum sound. hums regardless of volume control setting. input jacks/wiring are ok. hums from the preamp send jack, too. no power amp in /return jack. could the hum be coming from the power supply filter caps (1000uFx63v)? there aren't a ton of components in this amp....hand-wired chassis mounted pots, too. it looks nice inside.

thanks,
aris

[Rob Mercure]

I'm not sure where you are and what your power line frequency is but "hum" comes from one of two sources: the power supply - where the frequency will be twice that of the mains; or externally from the mains where the frequency will the same as the mains (actually, the same frequency can also come from the heater supply within the amp).

So, what's the frequency of your hum? If you stick a guitar cord into the input - no guitar - and touch the tip the loud noise you hear will be the same frequency as the mains. If so then you've got hum coming in either from the heaters or externally. But if the hum is of a higher frequency - an octave higher actually - then the problem is power supply hum which may very well be the 27 year old filters, or something shorted that's pulling down the power supply (smell any smoke? Any excess heat or sparks, "la cucuracha baracoa?").

Rob