tube testing oddity

Tung-Sol

Which brand?

Thanks for the advice but these are not NOS. I can buy new ones for $30 each. Just curious why a matched quad would exhibit such a pattern. I could see it if one of them was doing it, but all four at the same time? Very odd indeed.

88

I understand that Vintage Tube Services will put your tubes through a battery of tests for $15 each,Might be worth the time and money.

I personally have had situations where my tube tester has failed me. I've had tubes test well and than blow a fuse in my amplifier and I would have to locate the bad tube by trial and error and replace it. I never had your situation, but just guessing, there is a possibility that once the tube filament becomes heated, the tube is leaking emissions. I am very curious about this anomaly, I hope someone out there can provide a definitive answer.