[AMPS] Bypassing Screen of 4cx800a for 50 MHz

Steve Thompson g8gsq@qsl.net
Tue, 18 Dec 2001 18:51:27 -0000

-----Original Message-----
From: Lamb <k7fm@teleport.com>
To: Steve Thompson <g8gsq@qsl.net>; amps@contesting.com
Date: 18 December 2001 12:47
Subject: Re: [AMPS] Bypassing Screen of 4cx800a for 50 MHz

>Steve asked:
>"This is an honest question, not a carping comment. Is bypassing the
>to ground at -350V easier or less critical than bypassing the screen at
>You were probably always causing problems for your teachers - asking
>difficult questions just to see if you could stump them.

Only when I wanted to understand something better. Interestingly, sometimes
my questions elicit no response at all.

>The 4CX250 has 4 cathode pins.  So, if you are cheap and do not want to buy
>the proven, but expensive, socket with the built in screen bypassing, then
>it should be easier to bypass the cathode - since you have 4 shots at it -
>to get a low inductance bypass.

Indeed, Rich and Mike made much the same comment. The view appears to be
that it's not as critical as screen decoupling. That's what I had thought,
but imperfect cathode decoupling puts a reactance rather than a resistance
in the way. The volts across the reactance will reduce the gain, but it also
offers a point where signals can get fed back to the grid. I wondered if the
phase element might be troublesome - in practice, I guess it isn't.


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