Short the input RCA jacks and see if the hum is there.
If so its the preamp, if not its your CD player or cables.
Not your power amp.
Yes some tubes are microphonic, some tubes hum.
Carefully swap the L and R channel tubes and see if it moves with the tubes. If not, then send the amp back to Audio research and have them check signal grounding.
I find Marakanetz's post about Audio Research recommending NFB resistor change to be shocking. Changing NFB to tune overall gain can shift the oscillation pole frequency and can cause stability issues.
If so its the preamp, if not its your CD player or cables.
Not your power amp.
Yes some tubes are microphonic, some tubes hum.
Carefully swap the L and R channel tubes and see if it moves with the tubes. If not, then send the amp back to Audio research and have them check signal grounding.
I find Marakanetz's post about Audio Research recommending NFB resistor change to be shocking. Changing NFB to tune overall gain can shift the oscillation pole frequency and can cause stability issues.