[Ron Ramirez]

...is there any difference in hum pickup at the two locations.

No idea.

Another thing you might try is reversing the power plug in the wall socket...

Tried that. I had it plugged into an APC P11VNT3 surge protection power strip. Tried both ways. In one direction the tuning meter turned white once for about half a second, the stayed green.

I then tried plugging it direct into the wall outlet. In one direction, Auto Magic would not work at all. In the other direction, it worked for about three seconds before quitting again.

Well, it will be taken back to the basement. I need to replace all of the electrolytics in the tone control board anyway. When I get ready to do that, I will also do some more research into the Auto Magic circuitry. Perhaps I should attempt to remove and clean the tuning control shaft and its associated collar. I wonder if it originally used some sort of conductive grease, and perhaps that is failing, causing it to block rather than transmit the stray hum?