TESTING THE 12AU7 ON VARIOUS TUBE TESTERS
INTRODUCTION
Take a batch of tube testers, all in good working order and carefully calibrated following
the manufacturer’s instructions. Separate them by type— mutual conductance testers in
one group, emissions testers in another. Wouldn’t you think that if you ran the same tube
through all of them, you’d get comparable readings from all of the testers within their
respective groups? That would be logical— and wrong. As it happens, each individual
tester applies unique conditions to a tube under test, so readings from tester to tester, even
on the same model, will not necessarily be comparable. Not only that: readings obtained
on mutual conductance testers other than laboratory models usually won’t match those
published in standard tube manuals. Why? Because manuals assume a set of operating
conditions that most testers simply cannot duplicate.