Shorting Plugs and Non-shorting Plugs - Wothwhile?

Actually, no, I haven't listened to the amp alone. I did,however, listen to the preamp alone (with headphones, and everything else unplugged), and I still got the hum. That, for me anyways, rules everything but the preamp. Believe me when I say I've tried just about everything.

Disconnecting the preamp, and temporarily relocating is the only thing I haven't tried.

I thought I had cured the problem, too, by leaving the preamp on, suggesting that the problem was thermal in nature. But no. One of the things that makes this problem so hard to solve, is that it's sporadic. It makes it very hard to find a hard fault that can be isolated. Every time I think I have it solved, it comes back. Maybe, if I have about 45 beers, I won't care...

I guess it's the preamp. Just the preamp hummed using the radio test as described by Dan Myers. I like black and white tests like he describes. I can make a determination, and move on to my next step. Whatever that is. It just may be a new phono preamp, plugged into the (silent) tape inputs.