Data sheets for most indirectly heated cathode tubes tell us that a
warmup time of 3 minutes minimum is required for the cathode to reach
operating temperature. Yet, I believe I was told that Collins did some
work to speed this up to allow PTT of the filament of this type tube. I
think it was in reference to the 4CX600J used in an airborne KW linear
amp. Possibly, this was actually part of the design of this amplifier.
If this is true, it sure seems like the life would be shortened by this
type of operation.I believe the guy who told me this mentioned some sort
of programmed current ramp up to protect the tube. Is my memory playing
tricks on me or does anyone have knowledge of work in this area? I do
not like to think of how many times I have waited on my 8877 to warm up
while a rare DX station was calling CQ or getting ready to QRT. 73,
Dan N5AR
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