Hello All Fellow Amp Builders- I agree that it is best to allow the 8877
adaquate warm-up time ahead of the application of high voltage, even when in
full cut-off (of course). But equally important in my opinion is to have a
filament step-start circuit. Initial application of filament voltage is a big
stress on the filament. That is one reason why it is stated not to have a
filament transformer with more capacity than 10 amps. At cold start-up the
filament resistance is extremely low. It is my opinion that reducing this
initial shock to the filament will add to tube life. The tubes normally have a
long lifetime in continuous commercial service (barring other issues that may
occur) partly because the filament is not stressed from daily turn-ons. I
always incorporate a filament step-start circuit in my builds.Byron W5FH
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