Originally Posted by
HCSGuy
I don't have any experience with vintage tube stuff, so I can't give you any advice on repairing your equipment, but hopefully can help with troubleshooting.
If you disconnect the inputs to the amps, so it's just the amps connected to the speakers, is there still hum? If yes, you have an issue with one of your amps.
If not, connect the preamp, with no sources - does the hum appear? If yes, and it is only out of one speaker, then swap the preamp outputs Left to right - if the hum moves to the other speaker, the problem is with the preamp. If it stays, the amp is suspect. I'm assuming your vintage stuff does not have a 3-wire grounded plug, so the chassis are the neutral/ground, which would mean the RCA cables ground them together, so playing with a ground wire wouldn't do anything.
If you still don't have hum, plug in your sources, one by one, and test them. The most problematic sources are those that that get an input from somewhere else - cable boxes used to always cause hum, satellite receivers sometimes, or anything with an ethernet cable or external/mounted antenna may be causing a ground loop, but let us know how far you get with the first steps.
Hope this helps.