[Mondial]

I wonder if there is anything different between the AC power or grounding at your bench location and upstairs?

You mentioned that even with the diodes installed the Auto-magic worked fine at the bench, but stopped working when you brought the receiver upstairs. Since the circuit depends on picking up the stray hum voltage present on your body, is there any difference in hum pickup at the two locations.

 Another thing you might try is reversing the power plug in the wall socket, as one side of the line is connected to chassis through the 2.2 meg resistor. Depending on whether this resistor is connected to the line or neutral side may have some effect on the hum voltage activating the Auto-magic circuit.