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[AMPS] Heater potential

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Subject: [AMPS] Heater potential
From: (Rich Measures)
Date: Sun, 8 Mar 98 11:18:08 -0800
>Hi i have'nt. 
Thanks, Stan
>I have had no reson to "poke" around inside my
>2500E. And with all the fast,friendly help that I get from Command
>Tech.(not to mention that my amp is still under warranty) I would just
>ship it back for any repairs that might be needed.
Two owners reported to me that they experienced primary grid emission 
problems after theirs were several years old.  .  .  {Primary grid 
emission is due to barium oxide being deposited on the gold plated grid, 
due to barium oxide evaporation from the cathode coating.  The condition 
is indicated by a steady decrease in power out when the amplifier is 
keyed down.  As the grid heats during keydown, the barium contamination 
emits wrong-way electrons}  .  The condition was traced to excessive 
heater potential being applied to the 3cx800a7s.  .  The Dentron DTR-2000 
suffered from the same malady.  >5.9v was applied to the 4.75v to 5.25v 
rated heater.  The fix for barium contamination of the grid is tube 
replacement, and to lower the heater potential to within Eimac ratings.  
-  When one of the owners of the Command amps. told the factory that the 
measured heater potential measured close to 15v, the service dept. 
allegedly told him it was perfectly normal and not to worry about it.  
-  Maybe Command Tech. corrected the problem, or maybe they have not.  It 
would be nice to know the answer.  As I understand it, measuring the 
heater potential in one is not easy.  
-  later, Stan  -


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

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