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 I had assumed that since your amps were 'tested at the factory' that they had a clean bill of health. But the first rule of troubleshooting is 'don't make assumptions'. Occam's Razor is always trying to get me to look at the simpler explanation, and @redhouse6 's comment about the filter caps is a very good one! A lot simpler than most the other explanations here, including my own. So how old are your amps?
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The responses I read all seem helpful. I had a LF hum that drove me crazy. Don't know if this is relevant to your situation, but mine was caused by interference from my wireless router that was close to my equipment stack. The router was at the same level as my TT and the interference was picked up by my Lyra Kleos cartridge. I relocated the router to a lower height and across the room and it was gone. Go figure |
Yes, like a Triplite. They make quite a few different devices and sizes, so I don't know the specifics of the one you are speaking of. I bought a Triplite to isolate some testing equipment I was working with on a train.
Bringing your equipment into your office or a friend's house will be the free option. I would try that first, before purchasing anything. |
@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. |
