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Re: [Amps] GI-7b issues

To: Robert Perdue <>
Subject: Re: [Amps] GI-7b issues
From: Larry <>
Date: Tue, 09 Sep 2008 12:24:55 -0700
List-post: <">>
The cooling in those conversions is nowhere near enough.

The GI-7B anode cooler is not very efficient. It cannot be properly 
cooled with a fan blowing at it. In order to realize any decent 
reliability you MUST use a pressurized chassis with proper air flow 
around the base and through the cooler and the blower MUST be a 3 inch 
or larger squirrel cage turning at 3000 RPM or more.

I've done extensive testing of the GI-7B in a static test setup and 
compared seal temperature against actual anode dissipation and air flow. 
  I did this after having some of the same problems in my 432 amp that 
you have experienced. See the 432 GI-7B amp on my web page. The result 
of the testing was a rebuild of the air system so that the tubes didn't 
run away and self destruct.

Good luck.

Larry - W7IUV

Robert Perdue wrote:
> Looking for any info on the GLA-1000 conversion to the GI-7b tube. I have 
> done the w4emf conversion but I am having problems with the tubes self 
> destructing. has anyone else had issues with this tube? The amp runs fine and 
> then boom the tube melts down without any indications I have watched current 
> draw very close and that seemed fine but the tube just fails with a pop it 
> melts the solder out of the tube around the Anode cap. Could it go into 
> oscillation causing this? And for some background I ran the filaments for 48 
> hours before use. I have got 4 more tubes ready to go again but would like to 
> find the problem before proceeding. Anyone else having failures?
> 73, Bob kc0hfl  
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