> 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.
> 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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