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RE: Question on testing 12AX7s - gm vs. mA

Well, gm minimum for 12AX7 is very clear at 875, but very few read that low. As a (related) aside, I once got a boxful of used, rejected tubes (mostly Russian of various guitar amp brands) from a local amp repair guy. All the tubes tested at 0.6mA or lower, though gm was still "acceptable". Most were disposed of, but there were a few good ones above .9 in the box. My original question remains, how important is mA draw if the 12AX7 pulls half of new mA at these standard 539C settings? "Half of new" sounds like "bad", regardless of gm over 1100. :)


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