• WARNING: Tube/Valve amplifiers use potentially LETHAL HIGH VOLTAGES.
    Building, troubleshooting and testing of these amplifiers should only be
    performed by someone who is thoroughly familiar with
    the safety precautions around high voltages.

6j4 oscillating?

Status
This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.
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 1000µ 1626 cathode bypasses for a more sensible value (22µ) 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
 
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
 
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
 
Status
This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.