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In Reply to: RE: Tube strength and readings posted by Maddnotez@gmail.com on September 07, 2014 at 16:59:56
Hmmm may be an arbitrary meter?
Most Ebay tube guys use emission testers -but if the results represent GM (transconductance), then 1250 is not NOS (unless someone tested the tubes on a 100 V tester - but that would be strange).
1600+ is the number (GM) you want for 12AX7, 1200 for 5751 assuming 250V testers like the TV7 types and most Hickok testers etc.
Paul
Follow Ups:
That assumption on Hickoks is not quite correct. The plate voltages used varied widely between models as did the minimum acceptable values. NOS/NIB tube values also vary considerably out of the box...not all will hit that magical 100% mark. The manu's (RCA, Syl, GE, Tele, etc) listed numbers in their respective Tube Manuals were avg's based on typical used voltages. The number of variables preclude assigning a "correct" number.
jstrm
True...although a bit contrarian of you. My statement included the operative word "most".
Not every single mutual conductance Hickok tester utilized 250 V.
Within stated parameters, a NOS tube will hit the magic number - whatever number that may be for the given tester and tube. A magic number exists - it just is not the same number for all testers...but for most testers - ah, I digress :)
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