[Amps] 8877 Warm-Up Period

Byron Tatum bjtatum1 at att.net
Mon Jan 23 17:01:43 EST 2023

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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