Tube spark question

[Randall]

Gentleman, I have a 65 Deluxe Reverb in with a blown mains fuse. I replaced the fuse, and have been monitoring it and watching current draw. So far, it has not risen above 0.65 amps at idle, so I suspect there is no problem other than the old fuse just blew as they sometimes do.

But, during testing a curious thing happened. I tapped the rectifier tube and one single blue spark happened with a crackle in the speaker. I have tapped many times since then, and it remains stable. Then later I tapped one of the power tubes several times, and the same thing happened, one single smallish blue spark with a crackle in the speaker. THEN, the same thing with the other 6V6. Each time, one single smallish blue spark and then nothing after that. I have been tapping for two days now, and no more sparks. It bears mentioning all three tubes are vintage RCA.

So I wonder, what's up with that? Seems like the tubes are good. Did I jar some space dust loose that burned up by tapping? I am inclined to return the amp without replacing these RCA tubes, but I'd like to have a grip on why they each sparked one time only. The amp idles hours on end at just over 0.6 amps.

[xtian]

Did I jar some space dust loose that burned up by tapping?

That would be my guess.

[The Dude]

That would be my guess too, if you can no longer replicate the problem. Are there any signs of vacuum loss (i.e white gunk forming inside the tubes)?

[loudthud]

Were the tubes hanging upside down like they normally do when the amp is being played ? Just w0ndering if that has any bearing on the problem,

[Helmholtz]

Was the blue spark always happening in the rectifier tube?

It is extremely unlikely that all 3 tubes contain conductive particles.
Are power tube screen resistors good?

[Chuck H]

Was the blue spark always happening in the rectifier tube?

It is extremely unlikely that all 3 tubes contain conductive particles.
Are power tube screen resistors good?

I was thinking the same thing. Seems odd each would do this once and then never again. I'm thinking that one tube is doing it and tapping the others instigated the problem anyway. I'm thinking maybe a less than ideal pin contact on one of the 6v6's.

[The Dude]

At any rate, I would clean and re-tension the octal sockets just to be sure it's not a socket problem.

[Randall]

All three tubes (rectifier, both 6V6s) did it once each, and then not again. Cleaned all sockets. Idle current good on both 6V6s, adjusted to about 20 -22 mA. Not a vacuum issue. Tubes still in cab in normal hanging position.

I'm sending it out.

[Mars Amp Repair]

I don't see where it was mentioned if the tubes are old or new or if the getter spot on the side of the tubes is still bright silver or beginning to turn brown.
The Getter material doesn't always grab all the impurities on a new tube & sometimes you will get an initial spark as they get wedged between elements, but typically if that is the case, they burn off and you're good to go,
On older tubes I would typically replace them if there were any sparking going on considering their age.
Just a thought....glen