>In regards to key down time on amplifiers:
>I believe any amplifier can run keyed down indefinitely given:
>1.) Proper cooling of the tube to keep it within temp limits
>2.) Heavy duty enough power supply (the tube isn't the only thing getting
3) If an oxide-cathode tube is used, the key-down cathode current rating is
not exceeded. For example, a 3cx800a7 can handle 800mA intermittently in SSB,
but it is rated at 600mA in N-Ø-N/key-down service.
4. Provided that one does not do it into an antenna.
>If these two things are done, then there is really no reason why the amp
>can't be run continuously.
>If you doubt me, realize that a lot of
>broadcast stations use tube amps even today. These ARE keyed
>continously. They also have massive cooling and power supplies.
>While my tube amplifier experience is limited (eg: my 4-1000A), I have
>many years of solid state amp design experience. There is nothing in
>the RF design of an amplifier that would preclude it from running
>Just my thoughts.
R. L. Measures, 805-386-3734, AG6K
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