OK, first off I know that tube testers are limited as to usefulness, especially simpler ones. That being said, I picked up a Mercury 990 for not too much money, which just does basic shorts test and cathode emissions. It seems to work fine for 6L6 and 12AX7 tubes, but the meter doesn't register anything when using 6550 type tubes. I have tried it with GT 6550s and JJ KT88s.
Thoughts?
Thoughts?
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