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Audible low level humm from Vincent st-70

I'm experiencing a low level hum from my speakers when connected to my Will Vincent st-70 that is audible when not playing music. It is constant and does not increase or decrease with volume setting. Replacing the amp with a SS amp eliminates the humm. I have tested all the tubes and replaced the ones that showed weak. All current tubes show strong with two of the Kt77's showing minor grid leakage but still well within the good range. Humm is in both channels. The amp sounds great but I find the humm annoying between discs. Even though my GZ34 rectifier tube tested good could it be the problem?
ces4x4

Showing 1 response by newbee

newbee
4,751 posts
 
Re the hum - it certainly could be the power tubes, although that has never been my experience if they all hum at the same level. If the hum is at the same level in both channels it could be a speaker sensitivity issue (tube or amp noise threshold) or it could be a small tube problem. I've had small tubes (in a different unit) cause a hum but usually only in one channel, not both.

It could be a ground loop problem. Disconnect all of your sources. Then reconnect them one at a time using a cheater plug on the source PC and see if that helps. It did for me.
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