Tube Amp Hum

You don't mention if the hum is from the speakers or the amp. I had one of these on loan and the amp itself gave off a hum, not a transformer hum, but sort of like a hum from the tubes resonating (?), that could be heard from the listening position during quiet passages, after the amp had warmed up. Didn't try to solve the problem, just returned the amp.

try floating a ground on a power cable to see if it's a ground loop hum. swap tubes side to side to see if it follows a partiuclar tube. Check the outputs with a multimeter to see if any DC is getting passed in somehow.

many possibilities, search the archives here and @ www.audioasylum.com

-Ed