[Boatanchors] Question about testing tubes

[Richard Knoppow]

----- Original Message ----- 
From: "Rick Poole" <wa1rkt at arrl.net>
To: <boatanchors at mailman.qth.net>
Sent: Sunday, January 29, 2012 12:51 PM
Subject: [Boatanchors] Question about testing tubes


>
> Usually when I plug a tube into my TV-7 tube tester, let 
> it warm up,
> and press the designated "Test" button, the meter rises to 
> a certain
> level and there it stays.
>
> Sometimes, the meter will rise to a value and then slowly 
> fall off
> (whereas, for another example of the same type of tube, 
> the reading
> remains steady).  Assuming the reading does not fall below 
> the
> minimum specified in the tube test settings, is the tube 
> OK to use,
> or does the falling off indicate the tube is on its last 
> legs?
>
> Rick WA1RKT
>
     The instructions for the TV-7 say not to keep the test 
button pushed down for longer than it takes to make a 
reading and that doing so may damage the tube.
     A good test for tubes with weak filaments is to lower 
the filament voltage a step and watch the gm, if the tube is 
OK it will go up a bit at first and then fall off. I don't 
know the physics but its a legit test.


--
Richard Knoppow
Los Angeles
WB6KBL
dickburk at ix.netcom.com