[Boatanchors] tube testers

[Morris Dillingham]

I have a mutual conductance checker that has a rheostat adjustment to zero
the meter according the line voltage.  The individual elements are lumped
together versus the cathode to determine cathode emission.  By flipping the
element switches you can check the integrity of the individual elements
relative to shorts. It's not a very accurate method of checking the tube and
usually service manuals of tested products will tell you to substitute known
good tubes to be sure of the tube in question.  I would think that if you
can adjust the meter for zero, your meter is good and your rectifier is not
open, your checker would be as good or bad as any other of its type.  If you
want more serious checking, go for a transconductance checker.  I'm sure
that there are some tube checker experts that can give better advice.  We'll
see.  One late thought, if it is old enough it could possibly have a
selenium rectifier, often affectionately called a "seldom rectifier".  Could
have high resistance.

         73 de KI4IUA 
         Morris   


-----Original Message-----
From: boatanchors-bounces at mailman.qth.net
[mailto:boatanchors-bounces at mailman.qth.net] On Behalf Of John King
Sent: Thursday, July 14, 2005 2:36 PM
To: boatanchors at mailman.qth.net
Subject: [Boatanchors] tube testers

There has been a recent thread on capacitor checkers
and the need to recap the instrument to get the power
supply of the instrument up to specs, voltage wise, to
give correct test results.

I am curious if the need to rework the power supply of
vintage tube testers is appropriate as well.

I have a nice "old" B&K tube tester that is supposed
to be a mutual conductance tube tester. The test
results are questionable and most of the tubes that
test weak work as well as the ones with very good
meter reading. Very few tubes test as "very good".

This makes me wonder what is in the tube tester as a
power supply to test the tubes with. Seems to me if
the correct voltages are not provided to the tube
under test, that the reading would be inaccurate.

Has anyone checked their tube tester power supplies?
What did you find? Did you find the need to recap the
power supply, change resistors or bring the power
supply up to specs?

I would like the benefit of your EXPERIENCE with the
subject. Please don't ask me "is it plugged in".

I have more than one hundred tube receivers and
transmitters and believe me, a good tube tester is a
great help and a bad one is a liability. No one wants
to throw away good tubes. While substitution may be
the best test, a tester can give a fast test, if
reliable. Thanks for your input. You may email direct
or share your information with the group. All will be
appreciated. 73, John, K5PGW (since 1958)    

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