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TESTING THE 12AU7 ON VARIOUS TUBE TESTERSINTRODUCTIONTake a batch of tube testers, all in good working order and carefully calibrated followingthe manufacturer’s instrucTIons. Separate them by type— mutual conductance testers inone group, emissions testers in another. Wouldn’t you think that if you ran the same tubethrough all of them, you’d get comparable readings from all of the testers within theirrespecTIve groups? That would be logical— and wrong. As it happens, each individualtester applies unique conditions to a tube under test, so readings from tester to tester, evenon the same model, will not necessarily be comparable. Not only that: readings obtainedon mutual conductance testers other than laboratory models usually won’t match thosepublished in standard tube manuals. Why? Because manuals assume a set of operatingconditions that most testers simply cannot duplicate.
