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Re: [Amps] GI-7b issues

To: 'Larry' <>, Jim Kennedy <>
Subject: Re: [Amps] GI-7b issues
From: <>
Date: Tue, 9 Sep 2008 18:57:03 -0400
List-post: <">>
 Thanks for all the info on the cooling I do remember the tube running warm but 
it never seemed out of the ordinary. But at the time of destruction my hand was 
not on the amp. And yes the fan was running and I did build the enclosure but 
never paid much attention to the airflow (my fault) I have built 2c39 amps with 
water cooling and even a 1296 amp with a GI-7b that was water cooled so I am 
going to build up a water jacket and cool the amp that way. Thanks again for 
the help I guess I should have thought of cooling being the problem but 
overlooked it since the original conversion artical mentioned the stock fan 
kept the tube cool. 

---- Jim Kennedy <> wrote: 
> 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
> Cc:
> 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
> DN07dg
> 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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