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
http://w7iuv.com
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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>
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