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Old 18th January 2008, 11:50 AM   #1
Klimon is offline Klimon  Belgium
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Join Date: Apr 2005
Location: Leuven
Default 6j4 oscillating?

Hi,

I'm having some trouble with my double dc darling; it makes a quite loud very low buzz, regardless of volume setting; other than that the signal comes through cleanly. Sometimes the loud buzz stops after a few minutes.... I've had the same problem a few months back, then it misteriously disappeared. I just swapped the 1000 1626 cathode bypasses for a more sensible value (22) and when starting up (first time after some months) the buzz is back. I checked heater / signal / B+ wiring but don't think that's the culprit. The 6j4 tubes are only connected through one grid pin (it has three) using a grid stopper, dunno if I should connect all grid connections? Any suggestions are most welcome.

Simon
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Old 18th January 2008, 04:09 PM   #2
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Join Date: Jul 2003
Location: Ann Arbor, MI
hey-Hey!!!,
One of the high-gm signle triodes from WE has 4 grid pins. Suggestion to keep it from oscillating is to use a 1k carbon comp on each one( though you'll probably wish you could put the R inside the bottle ), and connect the signal to the pointy end of the 'Tee-Pee'. Same thing goes for the russian 6S45 too.
cheers,
Douglas
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Old 18th January 2008, 09:32 PM   #3
Klimon is offline Klimon  Belgium
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Join Date: Apr 2005
Location: Leuven
I'll insert some grid stoppers but there's still quite a difference in transconductance between a 6c45 and 6j4, I wouldn't think the latter that difficult (but we'll see). What's odd is that the buzz is always heard or stops through both channels at once. Unless one oscillating driver tube would trigger the other one the problem might be elsewhere.

Simon
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