> Since most commercial broadcast transmitters use directly-heated
> cathodes, warm-up time is not much of an issue. Many transmitters
> use time-delays that far exceed what is required in order to apply
> excitation to the PA and IPA. That said, glass tubes used at HF
> may fare better than the example described above, but the cost v.
> benefit cannot be justified even in the most intensely competitive
> major markets.
Most of the TV transmitters used indirectly heated filaments that
had significant warm-up time. Timers were typically 10 to 15
minutes although manufacturers often specified the filament time
at 5 to 7 minutes.
When spots in an NCAA "Final Four," Super Bowl, "local" university
football game, World Series, etc. were going for enough that the
loss of revenue from one 2 minute local break may have represented
the salary of the most highly compensated staff person, "hot
stand-by" was not even a question.
Now that most UHF transmitters use paralleled amplifiers to make
the necessary power levels and most of the new VHF transmitters
are solid state a "hot standby" isn't as common but I know a few
places that still run them.
... Joe, W4TV
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