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Question on testing 12AX7s - gm vs. mA

I acquired a Hickok 539c tester a while ago, calibrated by local expert. It has current measuring capability. I test a LOT of tubes but the common 12AX7 is sometimes a mystery. I get tubes that will read high in gm, say 1300 but only pull 0.5 mA current. Others might test 1100 gm but pull 0.9-1.0mA. The 1.3 grid volt setting is sensitive.

Anything below 0.6 mA, I usually toss. But they still sound decent in amp circuits. Which reading is more important for 12AX7, gm or mA?

Thanks for advice.

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Topic - Question on testing 12AX7s - gm vs. mA - PeterI 09:32:39 04/05/17 (6)


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