Re: VTTC Operation and Filament Warm-up

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: "Ed Phillips by way of Terry Fritz <teslalist-at-qwest-dot-net>" <evp-at-pacbell-dot-net>

Tesla list wrote:
 >
 > Original poster: "David Speck by way of Terry Fritz 
<teslalist-at-qwest-dot-net>" <dave-at-davidspeckmd-dot-org>
 >
 > Ray,
 >
 > My high school physics teacher (with whom I did a lot of Tesla projects
 > about 35 years ago) previously worked for Sylvania, making picture tubes.
 >
 > He said that applying HV before the filaments were fully warmed up would
 > tend to strip the emissive coating from the filaments, causing internal
 > shorts in the tube and limiting the life of the tube.  I agree that 833
 > filaments, being direct heated, would not require a very long preheating
 > time.  OTOH, some tubes, like my CX1159 thyratron, specify a 10 minute
 > warm-up before operation.
 >
 > HTH,
 > Dave

	The application of plate voltage before the cathode (filament or
indirectly heated) comes up to temperature can indeed cause significant
damage, as can turning the filament voltage off with HV on.  In the days
when we build airborne military radars using tubes there was a
one-minute warmup delay between application of heater and plate power.
Those were small tubes, none larger than a 6L6, but the USAF thought it
used to have a significant improvement in reliability.

	In the "good old days" when tube type equipment was used in
air-to-ground communications the FAA ground stations left heater power
on continuously, although it was later discovered that in some tubes
that caused damage to the cathodes.

Ed