REL subwoofer with old McIntosh tube gear?

Thanks Al. Are you sating I should jumper both amps from common to ground even though the black wire from the REL is only connected to one?

Thanks very much. I'm assuming there should never be a hum...even a slight one?

I'm saying that if I am correct in assuming that the red wire from the sub is connected to the 8 ohm tap of one amp, and the yellow wire from the sub is connected to the 8 ohm tap of the other amp, then what you should try is connecting the black wire to a ground point on the PREAMP, such as a chassis screw. But you should only do that with the COM and GND terminals of each of the two amps jumpered together.

Regards,
-- Al

Got it...I'll try it. Thanks!