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[AMPS] RE: 3-500z cooling

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Subject: [AMPS] RE: 3-500z cooling
From: (Phil (VA3UX))
Date: Sat, 29 Sep 2001 10:51:39 -0400
At 05:44 AM 9/29/2001 -0400, Tom Rauch wrote:

> > No, it was the technically correct way to do it.  The tubes could be
> > put into continuous service in some application (drivers for an AM
> > broadcast transmitter for example) at 100% duty cycle, hence proper
> > cooling was absolutely required to provide reasonable life.  Hence
> > Eimac's recommendations.
>respectfully Phil, the correct way to do it is any way that maintains
>the envelope and seals below rated temperature.
>How you do it does not matter.

Understood Tom.  I really didn't express my point very well with my first 
post.  There's no question that as long as air flow maintains proper 
envelope and seal temperatures, it doesn't matter how the air is 
propelled.  What I meant to express was that as a manufacturer Eimac is 
expected to provide recommendations for a proper method of cooling that is 
tried, tested and proven.  Their centrifugal blower/chimney set-up was 
their method that met those requirements.  And it appears to be a pretty 
good method (although more expensive than the fan with horizontal air flow 
method).  That provided an off-the-shelf solution so that manufacturers 
wouldn't have to engineer their own cooling system.  Of Course that method 
doesn't exclude the possibility of other and different cooling methods 
producing the same result. And of course (and as you pointed out) there are 
plenty of examples of simple fan cooling that have proven perfectly 

There !  That's what I was thinking the first time but didn't say until the 
second time.  The difference between a Friday night and a Saturday morning.



> > The fan aimed across the envelope and filament pins work fine in
> > amateur service where the duty cycle is generally low, low, low.  If
> > you ran RTTY for an hour or so at full output with the fan method, you
> > might find the limitations of that cooling method quickly.
>Not so. Air flow is air flow.
>It takes a much larger volume of airflow to cool a 3-500Z with no air
>confinement, but you can do so at much lower static pressure and
>the air coming out is not nearly as hot even though it carries the
>same amount of heat. That is because it is more air volume.
>Any system can be done improperly. The right way to cool a tube
>is the way that keeps the temperatures below the ratings.
>Many broadcast transmitters do not use chimneys, and many do.
>73, Tom W8JI
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