Tube tests bad, then good 4 months later????

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In July I had one channel in my pre-amp go "weak and dull" sounding. A check of the tubes (Tele 12AX7's) with a B&K 747 found a weak linestage tube. One triode tested in the ? white area and the other just barely in the green. Popped in a new pair (Ei's) and the sound was back to normal.
Today, while testing some new tubes and needing to make some room, I tested the "bad" tubes before I tossed them. When you're talking $60 tubes it's hard enough to toss them when they go bad as it is. Well, this tube tested just fine. I let it warm up, stressed it, the whole nine yards - tests strong. I have yet to "listen" to it in anything (my pre-amp has too many screws!!!) but my guess is it'll sound okay - I just don't know for how long.
Never had this happen before, so I don't think it's the tester. I also tested the other one that was in the unit at the time thinking maybe I'd got them mixed up - that one tested as I'd written on the box.
I purchased these as NOS from a very reliable source, so I was a little surprised by what would be considered an early failure in the Tele 12AX7 world. So, should I rejoice that I have my $120 pair of smooth plate Tele's back, or should I toss it????

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Topic - Tube tests bad, then good 4 months later???? - vrogers3 20:01:28 11/27/05 (5)

Re: Tube tests bad, then good 4 months later???? - David Anderson 15:43:34 11/28/05 (0)

Jimmy is probably right, but the best tube tester.... - JimL 05:47:11 11/28/05 (0)

I've NEVER had a Tele 12AX7 go bad - Dave Pogue 04:11:19 11/28/05 (0)

Re: Tube tests bad, then good 4 months later???? - MIchael Samra 23:32:02 11/27/05 (0)

Re: Tube tests bad, then good 4 months later???? - Jimmy 20:28:54 11/27/05 (0)

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