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
dpop
293 posts
 

@hiend2 

Try using an extension cord and plugging them in on other circuits

ervikingo has tried that already.

hiend2's avatar
hiend2
450 posts
 

I has a trouble in my preamp similarit was exposed to a Large Magnetic field.

Take the amp to your office,

Try a solid state unit...

donavabdear's avatar
donavabdear
509 posts
 

@ervikingo Hate to say it but I keep thinking about your neighbors WiFi transmitter system. 

I spent 20k on buying 2x PS Audio P20 AC regenerators and I still have a hum. Also it is rare that 60hz is the only frequency usually you get a lot of 120hz the harmonic. Test to see your ground and neutral voltage should be very low if it is anything above 1 or 2 volts that could be it. Also a new TV or radio station in the area. I love tube amps but I'm thinking they are such a pain. 

dpop
293 posts
 

@hiend2 

Try a solid state unit...

ervinkingo has tried that already, and the solid state amps don't hum. Please look back at some of the past comments.

@donavabdear 

I love tube amps but I'm thinking they are such a pain. 

I agree with you, and that's one of the reasons why I no longer incorporate them into my systems.  

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.

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