bad preamp tube creating open ground?

[Tele-Cat]

I built a 5f4 clone three years ago and up until about three months ago, it had been trouble-free.

Three months ago, it developed an open ground, and the only sound out of it, was 60-hertz, as if a cord was plugged into the input and not plugged into a guitar. Didn't matter if it was attached to ANYTHING, it was LOUD 60-hertz.

I did everything I could think of to do, swapped tubes (which at the time didn't seem to help but I swapped them all at once - still it should have fixed it) and it didn't. I cleaned the little switch legs on the shorting part of the jacks and eventually replaced the input jacks. No dice.

Finally I admitted I was in over my head, and took the amp to a tech. He diddled with the input jacks and it was ok. For a week. Then it was back.

I replaced the jacks. No dice. I sent the amp to another tech who cleaned up some of my soldering and when I got it back, I got a nice, quiet amp - for about a minute. Then it was back to the usual only this time the volume controls had no effect on lowering the volume.

I called a third tech and he said I could bring it in but I should pull the phase inverter and see if it stopped. (it did). I then pulled v2 (by itself) and it also stopped. So I dug out some different tubes (mostly ANOS Phillips AX7s) and put them in.

The amp was quiet.

THe 2 AX7s I pulled were the long-plate JJS. Is it possible for those tubes to develop an open ground? I know some of you don't like JJs, and I'm not here to debate the merits, I just want to know if a preamp tube, JJ or not, can develop an internal open ground? Because while the problem appears to be fixed for now, I want to be sure the fix is permanent and not just a band aid.

Thanks in advance.

[MWJB]

Some JJECC83s seem to have had slightly thinner pins, leading to intermittance, do you think that the issue is an internal one, or simply intermittant contact between pin & socket?

Turn the amp up full, all controls fully CW, and gently rock the preamp tubes and see if you get any unwanted noise.

I have only seen a handful wth this problem, the vast majority are OK. But if the tubes in question are noisy, then replace them.

[Chuck H]

I've had some noisy tubes from both Sovtek and JJ. But I would think it a really rare thing to have several in a row. I think it's like MWJB said, an intermittant pin connection. Has anyone tried cleaning and retensioning the tube sockets?