2. amps-preamps
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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
atmasphere's avatar
atmasphere
11,942 posts
 

@ervikingo 12AX7s trade high impedance for more gain so could be sensitive to a variety of variables. So going to 12AT7s may well solve the issue. 

I've also found that the brand of tube can sometimes cause hum. For example a phono section I was working on exhibited a hum a few minutes after warmup. The customer had replaced the stock 12AX7 tubes with Brimars, which are supposed to be a nice tube, but for some reason, even though the filament supply was regulated DC, the tubes would hum. Replacing them solved the problem.

ervikingo OP
166 posts
 

@dpop thanks for adding my comments and past attempts.  Those links are very useful !  The reviewer said they are dead quiet.  Hoping I get that

@hiend2 @donavabdear thanks for the input

@atmasphere Can’t wait to get the tubes here. In hopes of staying away of issues like you mention, I ordered them from Manley.

Sure hope that solves the problem. I have tried so many things and never looked at that detail. Sometimes the simplest answer is the best one.

atmasphere's avatar
atmasphere
11,942 posts
 

Sometimes the simplest answer is the best one.

Yes- if more people understood Occam's Razor the world would be a lot calmer place to live.

ervikingo OP
166 posts
 

I wholeheartedly agree.  Funny, one of my bicycles is an Orbea "Occam"

Thanks for all your insights.  I'll post results after replacing the tubes.

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