Arcing

[chunkitup]

My 6V6 PP has a problem. I have completed the build 6 months ago and I play the amp every night. It has never given me a problem. Then last night I flip the stand by and CRACK. I see a flash so I flip the S/B off as fast as I can. I take the chassis out and power up once more because I cannot believe that "MY amp which I have been playing for 6 months without a problem", all of a sudden is messed up. So once again when I flip the S/B...crack and a flash of electricity. I take the 6v6's out and flip the SB and nothing happens, yea! The voltages are fine so the PT is ok. I put the tubes back in and try to see where the flash happens. I have included a pic and the flash is coming from very close to pin 5 on the far right tube. I have the screen B+(larger red wire) going to pin 6 of that same tube. So what do you think may be the culprit?

[drewl]

I'll guess bad tube since it doesn't arc with the tubes removed right?
But check for any debris on the socket holes or possibly a bare spot on one of the wires.
I know how ya feel...I have an 18w head I built last year which I haven't played much die at a gig last week.
turns out the power tranny went bad.

[Enzo]

Everything works until it doesn't.

Have you tried different power tubes?

Turn off the room lights when you power this up, it will make it a lot easier to see any arcing.

[chunkitup]

Alright, now I have time to reply. Yes it only arcs when the tubes are in. I only have 6L6's to swap in. Is that ok to swap in just to check? So the most probable culprit would be the tubes, correct? The max voltage for them(EH 6v6's) is 350v and I had 379 with 27mA of current. Would the higher voltage shorten there life? I will order some JJ's which handle up to 400v. Could debris on the socket arc only with the tubes in? Trying to cover all bases.

[Mars Amp Repair]

hello,
I'd try just separating the components & wires, physically, that go to pin 5 from the ones that go to pin 6 as the proximity might be encouraging arching.

Below about 1KV, proximity arching isn't really an issue, but you can still get a flyback voltage from the transformer that will be twice the B+ present.

If this amp is fixed biased, Pin 5 is negative with respect to pin 3, so that makes the voltage difference that much higher than the B+ or whatever flyback voltage that might be created.

Ya never know....does swapping the tubes move the arching to the other socket?

Have you ever wondered what brainiac decided to put the input control grid pin that usually runs negative right next to the screen pin that has a very high positive voltage on it?

Seems a bit crazy to me.

glen

[chunkitup]

Yes the amp is fixed bias. I stepped away from the amp for a day and now when I switched the tubes, like you said, to see if the arc switched sides. It did not. There was no arc at all. What does that mean?

[Konny]

To me, the parts around the socket are too close.

IŽd separate them and perhaps isolate the resistors with heat shrink, that should avoid arcing even if the air is very humid or so.