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
jea48
4,451 posts
 

 

@holmz
 
 
 
 you beat me to it...

 

@dpop

It kind of sounds like a low frequency motorboating oscillation.

This may be off the wall, but I seem to remember reading a thread several years ago, can’t remember if it was on Agon or AA where a guy was having an oscillation problem with a tube amp. Just going from memory someone asked what speaker wires he was using. What ever manufacturer, type, speaker wire it was it was causing an impedance mismatch for the output transformers for the amp. If it was here on Agon I would bet the Late @almarg chimed in and was the one that solved the problem.

Might be worth it to try a cheapo zip cord 14/2 cable and find out for sure.

zombiedad's avatar
zombiedad
27 posts
 

That happened to me a month ago,  I heard the hum through both of my speakers, very annoying.    That hum noise was from my KT88.    Later I swapped my tubes to another KT120.    Noise is gone,  so quiet.     That was my fixed.  Nothing related to any ground, power conditioner.

If you have extra set of tubes,  try swap it and see if that helps.

 

dpop
293 posts
 

@jea48 

speaker wire it was it was causing an impedance mismatch for the output transformers for the amp.

Wow, these tube amps are more sensitive then I thought. Come to think of it, I was really into tube headphone amps for a while. I discovered that they too were very sensitive to headphone impedance, when it came to low level hum produced by the amp. I weighted the issue, and concluded that the headache just wasn't worth it. I was also many times hearing sporadic plinks, plunks, and noise bursts with tubes, and that drove me a little crazy too.  

ervikingo OP
155 posts
 

@jea48 + @dpop

It looks like the one I posted.

Mine is a TPS3A111000 (no superseded by TPS3A111002)

https://mall.industry.siemens.com/mall/en/us/Catalog/Product/?mlfb=US2%3ATPS3A111002

Thus:

voltage code: 120/240V, 10,3W

100kA per phase

EMI/RFI filtering (sine wave tracking), Ground integrated monitoring, Protection modes L-N, L-G, N-G, L-l

(whatever all of that means!)

 

ervikingo OP
155 posts
 

@zombiedad swapped the KT77 also swapped the 7044 and 12ax7 from one unit to the other.

I suspect that 12ax7 is the problem.  Speaker wires are AQ Rocket directional 18" long

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