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[Amps] setting the grid adrift

To: Tom W8JI <w8ji@w8ji.com>
Subject: [Amps] setting the grid adrift
From: Chris Howard <chris@yipyap.com>
Date: Tue, 25 Jul 2006 09:26:53 -0600
List-post: <mailto:amps@contesting.com>
> If you read the actual TEXT from Terman, he states the grid 
> will become positive.
> 
> Linky for you to tread:
> 
> http://www.w8ji.com/images/Amplifier/Bias%20and%20grid%20fuse/Terman.jpg
> 


Now that's an interesting piece of information, (And I note that
Will posted the same passage recently).

I have to object slightly to your assertion that the grid "will"
become positive.  The paragraph in question seems to assume a certain
condition of gas/ions/etc. to make it happen this way.

Thanks very much for scanning the text of Terman's and Giocoletto's!

Here's my latest newbie thoughts... just so you all can ride along
with me on my educational trip...

>From what I gather, loosing the grid from ground is not something
you want to do in the course of normal operation.  As a fault condition
it may or may not cause other things to happen.  And that makes
sense... the grid is your method of control, cut it loose and you
no longer have control.  It could float around near ground potential.
It could head straight for plate potential.  

Here is the conclusion I'm coming too:

Setting the grid adrift, if done in a system where there are other
controls on plate overcurrent, doesn't mean certain doom.
And there are some conditions where it might make sense, it seems to
have a higher sensitivity to certain kinds of faults that otherwise 
require more sophisticated detection methods (speculation).
And to me there is some engineering beauty to the idea of cutting off
the element that is suffering... everything everyone has quoted so far
seems to agree that loosing the grid will stop grid overcurrent.
But you then no longer have a working system so you might as well
shutdown HV and do a complete reset.

It's just another fault-control tool in the toolbox.
So whether or not you want to kill faults using that tool or some
combination of other tools is a design issue, not a moral one.

Am I getting there?

Chris


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