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[Amps] 8877 Warm-Up Period

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Subject: [Amps] 8877 Warm-Up Period
From: Byron Tatum <>
Date: Mon, 23 Jan 2023 22:01:43 +0000 (UTC)
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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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