Hey, I know these are noisy instruments, but I took mine apart for cleaning and to have the roller redone and putting it back together, the hum is at a point where it's overwhelming the signal. I've tried reversing the leads to no avail. It seems like I may have knocked a ground loose somewhere, but where? Anyone have any thoughts?

I think it's worked itself out somehow. It would seem it's back to the acceptable amount of hum and noise. I guess that's a question for another topic. From those with more expirence with this instrument, what is an acceptable level of hum and noise? LOL I know it's going to have issues, I just don't know how many are normal.

We just got one of these things to work on.

Personally, I'd not trust the power supply filter caps in anything this old. Our unit is from 1972, which makes 38 years since it was manufactured - and they probably used cheap filter caps, if the rest of the build is to be taken as any indication.

Replace the filters on the amp boards, and consider upgrading the rectifier diodes to something better (which is pretty much anything) than the junky silicon units that they installed in '72. Maybe some sort of quiet, soft-recovery rectifier like a HEXfred or something.

I will say, ours hummed like nuts when we first powered it up.. maybe that's normal, but to me it sounded broken / defective. The replacement parts are cheap and offer good peace of mind, so just do it.