Hum on Tube Amp - Can't find source

holmz    I didn't say it might be a ground loop, although it may be.

I did not say you did.

I said it. 😎

If OP reports correctly the hum is exactly 60Hz, the coincidence is too much.

If we had an Ishikawa chart we would see that a ground loop is  on the list of causal mechanisms. But we have possibility of one without the RCAs connected.

So that leaves incoming power, or the amps are jacked up, or some high current magnetic field near the amps... or ???

That's why I suggested to test the rig in another location

That helps identify the power and magnetic field.
If it sucks in location #2… then it points stronger to the amp being jacked up.

Power Conditioner in use or available to try?

@wsrrsw tried with Van Alstine Humdinger (for DC) but as described by FVA it only works to solve mechanical noise. I decided to try anyway. 
 

Also tried the iFi plug in things and even an old Tice thing (not the digital clock)  

waiting on a Zen Line Conditioner from Decware. 
 

Tomorrow planning on shutting down the alarm’s cell and wireless sensors. 
 

I went into the circuit breaker panel to confirm ground are properly connected. 
 

Next is taking amps to test at my office. 

what am I missing?

I suspect that it is the filter capacitors in the power supply. I used to fix tube TVs when I was a kid. 
 

You could also try an isolation transformer. 

Well, I can confirm it is not the alarm (which BTW I have reconnected!)

@redhouse6 like a Triplite?

I have a ZLC on order but it takes time to get it.