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Re: [Amps]  negative screen current

Subject: Re: [Amps]  negative screen current
Date: Mon, 30 Dec 2013 09:59:55 -0800
List-post: <">>
Peter asked...

> Question: Why do these modern ceramic tubes show negative screen
> grid current under some conditions? What is the mechanism that
> causes it? Straight thermionic emission from the screen seems
> unlikely, especially as a gold sputter would effectively prevent
> it.

It is caused by 'secondary emission' of electrons from the anode.  Under some 
conditions, more electrons are being gathered (by the screen grid) from the 
than from the cathode.  For a bit more detail without going into the physics 
mathematics of the phenomenon, see

for example.

I had remembered that this was covered in Eimac's 'Care and Feeding...', but I 
find it there now.  That shows the state of my memory, I reckon.


George T Daughters, K6GT
CU in the California QSO Party (CQP)
October 4-5, 2014

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