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My riddle of the humming V5 socket Sherwood has lead to some interesting findings.
In the V5 socket this happens.
If I put in an OLD tube - any old tube - there is NO hum.
If I put in a NEW tube - any new tube - it hums.
If I put in a NEW tube: the MORE hours it has on it - the LESS it hums.
There is a direct relationship to the number of hours on the tube to the loudness of the hum.
I've been burning in several GoldLion B759 tubes. It seems that at about 200-300 hours - that seems to be the NO hum point.
Any scientific reasons?
charles
Follow Ups:
Yes or no hum? Could be stronger testing 12AX7 types are amplifying the hum. Lower testing ones, not as much.
Just a WAG.
These are all new tubes tested by a reputable vendor.
I have several brand names and they all do the same thing. Diminish hum ONLY in the one V5 preamp socket of a Sherwood S-5000 with increased usage hours.
The hum output is directly related to the hours on the tube. I have several name brands and several of each brand tube with various recorded hours on them. All showing this phenomena. I could actual graph it!
charles
You haven't tried a new, lower mu tube, just to see if this is the issue?
But I don't have many new production, small triodes.
For old tubes that have been sitting around for decades they tend to be a little noisy for the first 48 hrs. I beleive this is due to the getter outgassing some impurities and when the tube gets hot they are reabsorbed by the getter. Usually a 24 to 48 hrs Burn-In will resolve this issue.
Groundhog Phil
I have seen many times where a tube that hasn't been used in years or decades needs 10 minutes to a couple of hours on the tube tester with just the heater energized to "wake up" and become a perfectly good tube. Low emission/transconductance before, perfectly good tube after. I have no explanation.
I you haven't cleaned the sockets do that. If you have, consider replacing it or adjusting it. Might be that the tube has pins that have a smaller diameter than the others you use. Hard to tell from here. ;-)
I think that your Gold Lion tubes are bad or at the very least not compatible with this piece of gear.
If I had to guess, I would say it's heater to cathode leakage.
It is possible for this to decrease over time as impurities boil off the cathode.
Some people actually measure heater to cathode leakage. I see no point. Either the hum is objectionable or it isn't. How many uA of leakage is required to hear the hum will vary from amp to amp.
Some amps use a hum balance pot to null this hum out.
This is also measurable. A lot of new Russian tubes will increase their emission over the first 50 or so hours you use them.
Are you in an anti-corrosion treated room?
(lol)
"I can't compete with the dead" (Buck W. 2010)
"It would take me forever. I don't think I have forever" (Byrd 2015)
No but I have been lining my room with thicker layers of tin foil to keep out the governments brain rays. It's a cover up because they're in it with the aliens!
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