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Ok the plate orientation theory didn't work out.
However ---- drum role please!
This is going to be like a minimal information brain teaser.
I have three matched new TungSols.
Two were used for about 200-300 hours.
One was not used.
I have Three matched Genelex.
One has 300+ hours and the other two are new.
When I put in the 200-300+ hour used tubes the hum is VERY low. The more hours the lower the hum. When I put the same brand tube in with NO hours it hums like a bastard.
Well getting closer.
Thanks for all the fun input.
charles
Follow Ups:
I'm sorry but I couldn't help but to ask - what song do they hum?
You could be dealing with an oscillation situation, the newer tubes might have a slightly stronger transconductance...
I have had oscillations cleverly disguised as Hum :> )
Stuben
Do you have a local station that goes off air at midnight and puts out the old test pattern, like they once did for TV, before paid advertising acts like an program?
Steve
Come to think of it I CAN see something that looks like an old Indian glowing inside that tube? Hummmmm!
Glorious new production tubes from Russia!
Have you tried any descent OS tubes in that spot?
The Genalex and Tung-Sol tubes he has are excellent tubes. The situation he's working with is a real weird one, and there are multiple threads about it where you can catch up on what has occurred and what has been observed if you want to. If you just want to be a bomb thrower you won't need to bother, but that's up to you.
Hi Jim.
You are right. In an earlier thread the OP states that the unit only hums with new production tubes, not vintage OS tubes.
Any ideas why that would be?
Honestly - no, I don't. I think the next step is to temporarily hook up that tube to a different heater supply and see if that changes anything.
The fact that the Genalex with the spiral wound heater hums (and now appears to be humming less as the tube gets time on it!) makes the step above a necessity IMHO.
This is a real brain teaser!
That's very interesting. Maybe with a bit more use the hum will disappear. Finger's crossed.
Are you adjusting the bias between tube swaps?
Thanks!
No, they are preamp tubes in an integrated amp.
charles
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