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[AMPS] 3-500Z amplifiers and grid current

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Subject: [AMPS] 3-500Z amplifiers and grid current
From: (Rich Measures)
Date: Tue, 17 Mar 98 03:18:37 -0800
>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

Only in relation to defective anode cooler welds, not to bent filament 

>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.
By what mechanism does an allegedly defective tube damage the parasitic 
suppressor R and blow the grid choke?
>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 have tested Amperex and Chinese [Penta] tubes that failed from a bent 
filament helix.  

>I suspect that I know the source of those tubes and amp which is why I
The two, new tubes came with the new TL-922.  
>Bang..yes...parasitic..highly doubtful.
Only if you can explain a plausible alternative scenario based on the 
circumstantial evidence.  .  Your serve, Carl.  


R. L. Measures, 805-386-3734, AG6K   

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