Hi Tony,
First thing I did was to plug it in my 1990's era computer AVR (relay type - heavy) along with my TT, CD player and lamp. Turned on the AVR and hum was evident. Unplugged it and connected it to my Panther surge protector, no humming or loud pop if i do the following:
1. Turn on the AVR first (TT,CD player, lamp)
2. Then turn on the surge protector and tube amp.
After Playing
3. Turn off the amp first
4. Unplug the surge protector
5. Turn of the AVR
Grounding issue?
I also must be careful not to touch any of the AVR and surge protector wires as the amp will suddenly make a loud pop or hum.
Thinking of buying a servo type AVR to plug everything but still unsure if it will solve the humming issue.