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Re: [Amps] ALPHAs and momentary power outages

To: "Paul Cassel" <>, <>
Subject: Re: [Amps] ALPHAs and momentary power outages
From: "Tom W8JI" <>
Date: Mon, 16 Jul 2007 09:33:01 -0400
List-post: <>
>> Has anyone hacked the Alpha circuit that would sense the 
>> duration of
> filament voltage loss and change the timer accordingly?

I ran into the same thing so many times I changed my timer 
in a homebrew amp to a ramped reset. I use a different 
current in the reset path of my timer, so the capacitor 
slowly discharges.

To be safe with my tube, I have a full warm-up reset after 
1/3 of the time Eimac requires for the warm-up time.

To be more exact, I use an op-amp comparator. The warm-up 
time is 5 minutes as a capacitor charges from zero to 66% of 
supply voltage. The pull down circuit is constant current 
discharge and takes the capacitor down to zero volts in 100 
seconds. In 50 seconds it takes about 2-1/2 minutes for  a 
reset. In 25 seconds only about one minute or so. In 5 
seconds off it takes 10-15 seconds.

You might do something like that. The key is to be sure the 
tube is at rated CATHODE temperature before reset, and you 
can't measure that externally. You have to time safely.

73 Tom

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