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Hum on Tube Amp - Can't find source

I have a hum (60hz) I can hear on my speakers and it happens with my tube monoblocks (either of them).  With or without interconnects, it even happens on either amp (have tried one at a time) with every circuit on the house tripped/disconnected, every other component disconnected from the wall (including the Internet/CaTV line) and no interconnects.  

One amp has it as soon as it warms up whereas the other one is intermittent.

Hum X doesn't solve it, iFi Ground defender either, AVA HumDinger on powerline  doesn't solve it either.

I have replaced the tubes and both amps were just tested at the factory.  Replaced the circuit breaker, tightened every wire on the breaker box, checked and cleaned all connections to ground rod.  Added a hum eliminator to the internet line.

Hum cycles a bit with the tube glow matching the cycles.

I'm waiting on the power company to come check the power coming to the house.

Thoughts?

ervikingo
holmz's avatar
holmz
2,328 posts
 

If nothing is plugged in (ICs) then it would be difficult to get a loop, so difficult to get a ground loop.

A DC bias on the AC line, usually comes across as transformer hum.
I ‘m not sure how it would come out of the speakers though.

ervikingo OP
142 posts
 

Only thing I cannot disconnect is the power meter and a whole house surge suppressor that is right after the power meter. I have a standby generator but it’s isolated when there is power by an automatic transfer switch. 
 

all lighting are LED but the noise is present with all circuit breakers (but the amps) tripped. 
 

I have no hum on my solid state monoblocks which share power outlets (for testing they are disconnected) and are located near by. 
 

Odd that it takes a bit to start. You see the glow of the tubes change. 
 

would speaker feedback do that? IRS Beta 

ervikingo OP
142 posts
 

Holmz,

 

I just tried VanAlstine humdingers on each and the problem persists. Please note, there is no mechanical hum on the amps; I have noise on speakers and the changing glow on the tubes. 

holmz's avatar
holmz
2,328 posts
 

Dunno… multiple tap points on the amp?
Changing glow is not encouraging, but it is useful.

Some tube expert might chime in. Like Atmasphere if you ask him nicely…

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cleeds
5,912 posts
 

You might want to try these amps in a different location to see if you get a different result, but I doubt you will. Even though the amps have been recently checked, they sound suspect to me. Many an amplifier or vacuum tube set have passed a bench check only to suffer some shipping damage on the way back to the customer.

What kind of amplifiers are they?

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