2. amps-preamps
  3. 192272-98100

Right channel phono stage tube goes noisy

I have a certain phono preamp, which shall remain nameless, that has exhibited a strange issue on the right channel. Of any brand new tested 6922 tube pair that I insert into the moving coil stage, the right channel plays quietly for about three hours, after which time I start hearing soft popping or crackling sounds that are audible from my listening chair. When I swap the left and right channel tubes, the noise goes to the left channel. Four good tubes have done this. The original MC tube played fine for about six months. I believe something in the circuitry is defective or has gone out of spec or otherwise has sort of failed and is maybe overdriving that tube. I sent the preamp to the dealer for repair. Some sort of modification was made but the problem was not fixed. They tested the first three tubes and they claim that they are fine. Has anyone 1) encountered such a problem, and 2) what was the fix? Was it simply a resistor or capacitor that had gone bad? 

earthtones
mulveling's avatar
mulveling
1,917 posts
 

That’s a tough one, and I don’t have any ideas beyond what’s been posited by others. Just wanted to say I’ve encountered more gremlin-y issues with 6922 / 6DJ8 tubes (and sometimes the components that use them) than any other tube type. F that tube type lol. 6H30 is better anyways for line stages, 6SN7 for drivers (or perhaps even better 5687 / 6BL7 / 6BX7), and 12AX7 for RIAA phono stages.

Of the 6922 tube variants, I’ve had relatively better luck with Siemens E88CC and Japanese Matsushita 7DJ8 / PCC88.

You want to drive yourself crazy, get a DIY T2 (extremely complex EL34 hybrid electrostatic headphone amp with +/- 500 Volt rails) with its 6922 quad on the input stage.

earthtones OP
110 posts
 

Thanks everyone, for the advice. The dealer is sending me a new replacement phono preamp, so I didn’t have time to try that left to right tube swap. But I will if it happens again. I was not aware of all the troubles with the 6922. I used to have a PS Audio BHK preamp that had them, which gave me no problems. I substituted a set of NOS Amperex 7308s, which were fine and that I would buy again, but in that unit, I had to flip a switch to change the bias voltage. I’ll have to find out if there’s any such compatibility issues with this unit, which doesn’t have that switch.

earthtones OP
110 posts
 

“That’s Odd??? Self healing tubes? What happened when you tried the tubes they tested back in the phono preamp?”

They said the tubes tested fine. But I’m quite sure they didn’t listen to them in my preamp, which I had sent to them. So, yeah, I’m confused about that. So I’m stuck with four pairs with one in each pair that’s of course still noisy.

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