> reduced voltage during the hours the transmitter was dark. I think it
> was something like 80% of normal voltage. They claimed it improved
> filament life by both avoiding the startup stresses as well as the wear
> of full power on the filament when not needed. (not to mention less
> power consumption) I don't know if this was ever put in to common
> practice, but I know it was used in some circles.
As I recall, a filament reduction to 80% is useful as "black heat" and some
high-power commercial transmitters have the ability to go into a black heat
mode during extended standby periods. This may be what Joe is referring to
with television transmitter experiencess. It makes perfect sense during
events like "Superbowl Sunday" with so much at stake, but in the AM/FM
broadcast side of the world, I think you would be hard-pressed to find many
stations that run their auxiliary transmitters in a hot-standby mode on a
regular basis.
Reducing filament E on a directly-heated cathode to below ~ 70% of the
normal operating value is like turning the filament off as phase transitions
in the filament structure reduce tube life as filament E drops below this
value.
Paul, W9AC
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