The principle used in the K4IPV power tube tester is very simple.
Testing the tube involved providing it with proper DC potentials, and
inserting a small and known AC voltage in series with the control grid bias.
The corresponding AC current in the plate circuit was sensed with a
series resistor or current transformer and the transconductance
was calculated as gm = AC plate current/AC grid voltage.
If the AC voltage was wisely chosen, the AC current indicator could
be calibrated directly in gm.
When a tube reaches the end of its lifespan, the gm decreases, which is a
sensitive indicator
for the tube condition.
At SK6AB in the early 80's I was involved in constructing a makeshift tester
for i..a. 4-1000A's
along these principles. It required some careful attention to high-voltage
precautions.
73/
Karl-Arne
SM0AOM
----- Original Message -----
From: "Jorge Gomes" <jorge-gomes@mail.telepac.pt>
To: "Karl-Arne Markstrom" <sm0aom@telia.com>
Sent: Saturday, March 04, 2006 7:34 PM
Subject: A request from Portugal (Was: RE: [Amps] testing 572 B tubes)
> Hello Karl-Anne,
>
> Well, you definitely got my attention with your comment to the list! I've
> been pondering this very same problem (testing transmitting tubes) for some
> time, in the process of "reawakening" some of my linear amplifiers, after a
> long inactivity period.
>
> Checking and eventually restoring their power supplies is fairly simple but
> I've been trying to identify an effective and reliable, preferably
> out-of-the-amp, testing method for the power tubes (3-500Z, 4CX-1000A, 811A,
> 572B, 8122, 4CX-800A).
>
> Could you kindly suggest a source, where I might buy a copy (paper or
> electronic) of the article you mention?
>
> Thanks in advance and best 73 from sunny Portugal (actually, quite rainy
> today, for a change...),
>
> Jorge
> (soon to regain the "active amateur" status, after a loooong QRT period...)
>
> -----Mensagem original-----
> De: amps-bounces@contesting.com [mailto:amps-bounces@contesting.com]Em nome
> de Karl-Arne Markstrom
> Enviada: sabado, 4 de Marco de 2006 11:16
> Para: alan.kaul@att.net; amps@contesting.com
> Assunto: Re: [Amps] testing 572 B tubes
>
> In "Ham Radio Magazine"April 1978 there was an article titled "Testing
> Power Tubes"
> by Joe Carr K4IPV (SK). It covered the basics in transmitting tube testing
> and evaluation.
> Recommended reading.
>
> 73/
>
> Karl-Arne
> SM0AOM
>
>
>
> --
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>
>
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