EL84 arcing?

[pezed]

I was trying out a bunch of old EL84's earlier.. one of them was shooting blue arcs inside the tube. Didn't seem to damage the amp at all but i was just wondering what causes this? Obviously it must be a bad tube, but is arcing caused by air in the tube?

[Bacchus]

Hey Pezed, I had the same issue with NOS Japanese Toshiba's, they would arc whenever I'd hit a chord!!! Fortunatly the reseller took them back without a fuss...

Too bad because I had high hopes for these tubes... The guy exchanged them for Canadian made Rogers tubes for the inconvenience and they are AWESOME!!!