#1
Hey Everybody

Ok I just got this old Univox solid state amp from the early 70's. Its kinda in good shape, with a spring reverb and tremolo and 2 ten inch speakers.

BUT there is a CONSTANT hum when I turn on the amp, with or without a guitar plugged in. Its quite loud. You can find a schematic here: http://www.abeltronics.co.uk/download.php?manu=univox&file=univox-150rx-amplifier-schematic.pdf
I wanted to post it but it too big....

So far I have replaced the power supply capacitor (the 2200 uf and 35V one, {the schematic says 2000uf but that wasnt what the actual part said}) and cleaned all the contacts.

Does anybody have any suggestions to what it could be? Should the amp become parts? THANKS
#2
It'd be hard to troubleshoot it over the internet. My guess is that one of the jacks is not closing properly.

Looking at the schematic, though. Only the "guitar" input is a shorting jack.

Another guess, I'd touch the chassis. Any bare metal on the chassis. If this gets rid of the hum, switch the plug out for a 3-prong grounded plug.