Twc, if your cable tv is nearby, you should also try disconnecting the coax cable tv wire at its first point of entry and then turn your rig on and see if the hum is gone. If there's no more hum, you need a ground loop isolator which will take care of this issue for you.
tubed preamp off and ss amp left on?
Why can't I leave my my ss amp turned on with the tubed preamp turned off? Loud hum occurs through speakers with this condition. When I had a ss preamp I could leave the amp powered all the time with the pre off. I would leave all powered up but concerned about the preamp tubes wearing prematurely. Is it a reasonable conclusion that I could leave everything powered on all the time and just change the tubes once per year?