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Re: [Amps] GI-7b issues

To: "'Larry'" <>, "'Robert Perdue'" <>
Subject: Re: [Amps] GI-7b issues
From: "Jim Kennedy" <>
Date: Tue, 9 Sep 2008 21:55:34 -0000
List-post: <">>
Hi Bob, I can only echo what Larry and the rest have said about cooling
GI-7B's. I converted my Henry 6&2 amp from the almost not existent
8874's to GI-7B's and dedicated 2 meter amp and found that the original
cooling was not near enough. The original blower just couldn't provide
enough air to prevent thermal drift. I replaced the original blower with
one that provided more volume and also additional cooling on top of the
chassis which resolved the problem. I have been running the amp now for
over a year on WSJT meteor scatter and EME without any further issues at
700+ out. There just isn't any substitute for lots of air. 

Jim W6OUU DN22  

-----Original Message-----
From: []
On Behalf Of Larry
Sent: Tuesday, September 09, 2008 7:25 PM
To: Robert Perdue
Subject: Re: [Amps] GI-7b issues

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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