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October 7th 03, 01:41 AM

In article , (Scott Dorsey)
writes:

Actually, some of the cheap Hickok units are real transconductance testers,
and some of them do show up for next to nothing now and then. They aren't
any TV7, but they sure beat out the drugstore testers.

Some of the emission testers are no better than drugstore testers, and they
have a tendency to indicate perfectly good tubes are bad, or vice-versa.
This can be extremely frustrating if you ask me. They'll find open filaments
and poor emission, but other problems (especially on beam power tubes) do
not show up on them.

Can someone explain how a tube can show good cathode emission, but not be up to
snuff in transconductance? A tube's performance depends on teh geometry and
structure of its grids and plate and their spacing. If hte tube hasn't been
physically knocked around, the geometry hasn't changed. So if the cathode is
putting out the electroncs, how can the tube not be up to snuff?

I know about grid emission and cathode interface.
BTW, I have a vintage 1928 Hickok that is indeed a mutual conductance tester.
It "does the math" with a two-coil meter movement.
--Mike K.

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