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Humming sound in SOME tube amplifiers

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Posted on May 29, 2016 at 23:11:02
howardyu
Audiophile

Posts: 61
Joined: August 9, 2006
 From time to time, I find special humming sound in SOME tube amplifiers. It appears in few seconds after turning on the tube amp, and disappear few seconds later.

1. May I know the cause of this humming sound?
2. How can I eliminate it?

Thank you!

 

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RE: Humming sound in SOME tube amplifiers, posted on May 30, 2016 at 12:25:33
Michael Samra
Dealer

Posts: 36118
Location: saginaw michigan
Joined: January 30, 2005
 If it appears for a few seconds after initial turn-on,that would indicate a power transformer buzzing most likely..You may need to tighten the screws on the bell covers...The reason it's hum may be so prevalent on startup is because the amp draws more current on startup and that puts a bigger load on the power transformer,especially if the transformer lams and core are loose.

If the hum comes thru the speakers,I would look for a rectifier tube or a small tube with heater to cathode leakage.It could also be a filter cap but that would be rare in this case.
"For every complex problem there is an answer that is clear, simple, and wrong" H. L. Mencken

 

RE: Humming sound in SOME tube amplifiers, posted on May 30, 2016 at 18:28:57
howardyu
Audiophile

Posts: 61
Joined: August 9, 2006
 Let me try tighten the screws firstly.

Thank you, Michael.

 

RE: Humming sound in SOME tube amplifiers, posted on June 7, 2016 at 01:20:54
howardyu
Audiophile

Posts: 61
Joined: August 9, 2006
 I find that the hum comes thru the speakers.

Could someone teach me how "a rectifier tube or a small tube with heater to cathode leakage" cause this problem?

Thank you!

 

RE: Humming sound in SOME tube amplifiers, posted on June 7, 2016 at 06:21:55
rogerh113
Audiophile

Posts: 507
Location: San Francisco South Bay
Joined: October 20, 2014
 I have the same thing on my SET. I always assumed that it was that brief transient time when the caps were stabilizing to voltage and the signal tubes were warming up. Now I would be concerned if I did not hear it. Previously I had a Primaluna power amp, and that had a timed relay (I think) that prevented signal through the amp until it warmed up - you could not hear anything until the relay tripped. My guess is that the noise artifact is there inside the amp as it warms up, and they are protecting the speakers (and your ears) from having to listen to that buzz. They might get the amps returned for service if people heard that and got concerned .....

Regards -- Roger

 

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