2. amps-preamps
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Tube Hum?

Hi Folks.
I just got a NOS pair of RCA Red Base 5692 (for 6SN7 type) tubes and installed them into my Blue Circle BC2 Hybrid monoblocks (they use a single 6SN7 type tube per monoblock). The tubes replaced standard Synvalia 6SN7s and the improvement in quality of sound was readily apparent - great upgrade.

However, there is a significant hum coming from one of the channels - I switched the tubes around to try and isolate the problem and it's definitely because of one of the tubes. The noise is not classic 'noise' like an intermittent hiss or static noise. Rather it is a deep hum. The tubes are NOS and supposed to be matched within 8%. Will this hum disappear as the tubes burn in a bit, is there anything else I can do to get rid of the hum, or am I stuck with it. Also, do you think such a hum is the luck of the draw or should the seller be responsible for providing a tube without such a flaw. Let me know what you think. Thanks!
John.
128x128outlier
yu11375
137 posts
 
By my experiences with 6SN7 tubes, sometimes (especially VT-231) loose bases generate annoying mircophonic hum. I tried to put some glue around the base to eliminate the problem. Also, the noisy hum won't fade away.

Hope this help.
elevick
2,636 posts
 
I agree, you have a noisy tube. Return it if you can. Don't try to glue it unless you have high heat glue? Last resort, I have an NOS pair of Sylvanias, interested?
fletchj
91 posts
 
Sometimes tubes, will act up, hum, hiss, spit, etc., in a certain circuit, and will be dead quiet, in another. Although the 5692, is an excellent sounding tube, and should be very quiet, some circuits, will stress it, that is why the GTA, and WGTA versions, were made. Any reputable tube vender, should extend a warranty, for a tube, that developes problems, in their initial use. I'd advise you, to contact the vender, and see what arrangements, can be made. Regardless, of the reason, you should expect that tube, to be noisefree.
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