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Re: [Amps] A request from Portugal (Was: RE: testing 572 B tubes)

To: "Jorge Gomes" <jorge-gomes@mail.telepac.pt>,<amps@contesting.com>
Subject: Re: [Amps] A request from Portugal (Was: RE: testing 572 B tubes)
From: Karl-Arne Markström <sm0aom@telia.com>
Reply-to: Karl-Arne Markström <sm0aom@telia.com>
Date: Sat, 4 Mar 2006 21:03:14 +0100
List-post: <mailto:amps@contesting.com>
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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