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[AMPS] G2DAF Circuit

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Subject: [AMPS] G2DAF Circuit
From: (Tom Rauch)
Date: Thu, 26 Oct 2000 20:02:24 -0400
> Hi Tom,
>    The 4-125 exhibits about 2.5K of grid impedance at 100V peak
> (positive) drive.  The pair will be about 1.25K.  This is a reasonable
> fraction of the input loading compared to the 300 ohm swamping R.
> 73,
>    Marv  WC6W

Hi Marv,

Can you tell me how you got that number, for a zero bias 4-125A 
with a voltage doubler hanging off the grid driving the screen at 
some unknown voltage?

According to tables, at 20 volts positive voltage grid current of a 
single tube is 10mA. At 80 volts, around 30 mA....but that's with 
350 volts on the screen. 

With less screen voltage, control grid current is much higher in a 

Are we assuming the doubler draws no current, and does not load 
the grid system? Are we assuming the control grid resistance with 
somewhere near zero volts on the screen (since the doubler draws 
no current) is the same as it is with 350 volts of screen voltage?


73, Tom W8JI

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