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[AMPS] 3-500Z amplifiers and grid current

To: <>
Subject: [AMPS] 3-500Z amplifiers and grid current
From: (km1h @
Date: Mon, 16 Mar 1998 20:13:55 EST
On Mon, 16 Mar 98 16:14:43 -0800 Rich Measures <> writes:

>>I am glad you stress that it is only an opinion Rich.
>What is your opinion as to why a virtually new Eimac 3-500Z would 
>generate a big bang and sustain a grid-fil. short?

>>BTW, what was the date code on that tube and did it come from the 
>date code 8939, NY was where it was shipped from, Carl, although I do 
>from which dealer the "new" TL-922 came from.

With that date code it does not suprise  we.....YOU, I and others have
mentioned many times that Eimac had definite problems with 3-500Z's in
'89. I can only relate a few of the hooror stories of the hams that
bought '89 tubes for spares only to have them go bang when used several
years later. 
Actually I commend your honesty about the date code Rich...others would
have tried to hide it.

I was buying 3-500Z's at 100 a time from Eimac then and even right out of
the box I had a high failure rate. It was around 1992 or so that I really
got feedback from those ...many good friends...that had decided to use
their "spares". and having big bangs.  
It was also at that time that I started a serious evaluation of all the
Chinese versions. Today...1998 I only buy Chinese.   Failures are
virtually zero..

Rich..and others is my "opinion only"...that a huge majority of
Eimac 3-500Z failures are due ONLY to poor quality tubes...NOTHING ELSE. 
I fail to see any failures with Amperex (1968 and later) or good Chinese
(1994 and later) versions that even approximate the Eimac experiences. I
stress the word ANY.

I suspect that I know the source of those tubes and amp which is why I

Bang..yes...parasitic..highly doubtful.

73   Carl   KM1H

 At the time of the 
>the 1A-rated grid choke opened.  
>R. L. Measures, 805-386-3734, AG6K   
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