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Tube Question--Slight Ringing coming from one side

I am running a pair of Klimo Monoblock amps, EL34 based. I baised them about 2 months ago, pretty much everything has remained the same except I had to move them closer together and closer to my turntable. Within the past 2 weeks, I have noticed out of the left monoblock a slight ringing (not really a ringing, but kind of like the sound of a refrigerator at idle) not at idle, but when the volume is turned up to a conversational listening level. it increases as the volume is raised

I have never experienced this before in this amp or any tube amp I've owned in 20 years. I thought of using a tube damper on the el34, but this is not addressing what may be a problem. Could it be the tubes are ageing? I was able to bias them exactly at factory specs 2 months ago.
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newbee
4,767 posts
 
I think Dc007 is correct, although I'm not sure I'd want to be tapping on a amp driver tube unless you are an experienced tapper. :-)

What I would recommend is doing a normal process of elimination. Just switch the driver tubes from one mono to the other and see if the noise follows the tube(s). If you have more than one small tube then reverse the process one tube at a time until the noise switches back. In so doing you would also be reseating all of the driver tubes and by doing so cleaning off any accumulated corrosion.

But, what ever works......
dogpile
118 posts
 

Try swapping tubes to isolate the culprit...left > right / right > left channels on both amp and/or pre amp. Eventually, you will find the microphonic tube.

Good luck!
muzcal
66 posts
 
I'm not familiar with these amps either but, unless they are integrateds, and the noise varies with volume level, I'd suspect the preamp. If it's the preamp then it would be a tube prior to the volume control. Again, as Newbee suggested,try switching tubes from one channel to the other in the preamp one at a time until the noise switches to the other channel.
dgarretson
2,594 posts
 
Persistent ringing is more common in small preamp & amp input tubes than in large power tubes. Flicking your fingernail (even somewhat sharply) against the tube, will usually reveal the culprit and eliminate the ringing for awhile. The juggling vibration of removing and rotating the tubes will probably also eliminate the ringing for a time. This kind of ringing is different from microphonics, and probably cannot be eliminated with damping rings.

Dave
atmasphere's avatar
atmasphere
11,753 posts
 
The complaint is a description of a microphonic preamplier tube, occuring before the volume control in the signal path. The amp has nothing to do with it.
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