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?
@atmasphere they are 20 years old. I just realized that the prior owner changed the input tubes to 12AX7 when the design calls for 12AT7. Thus higher gain (if my limited knowledge of tubes is correct) than what the spec for my particular version of these amps calls for. Could that cause the oscillation? I ordered a couple of AT7s to swap. Regarding the factory and I quote: The unit was biased and received a complete test. Unit passed all factory specs. |
@rhljazz Not treated. Thanks for the suggestion @papafrgog the closest access point is 20'away. I disconnected all wifi and low voltage and it didn't improve. Thanks! @redhouse6 I agree, I'll try on another location before buying something else. I have a collection of tools and tweaks which is getting expensive. Hoping the upcoming input tube swap finds the issue. |
@jerryg123 Can't confirm. Good question |
If your amp has them, make sure to run the rear impedance selector switches in the 15K position (it looks like not all Snapper models have them). It’ll be interesting to see if installing 12AT7 tubes has any effect on the hum. I think it will. I just stumbled upon a review of the amp: Soundstage.com Home Audio Equipment Review Here’s a few opinions on substituting 12AX7’s for 12AT7’s: Can I substitute a 12AX7 tube for a 12AT7?
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