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Re: [Amps] Direct-grounding SB-220 grids

To: Vic K2VCO <>
Subject: Re: [Amps] Direct-grounding SB-220 grids
From: R L Measures <>
Date: Wed, 7 Jun 2006 02:59:48 -0700
List-post: <>
On Jun 6, 2006, at 1:07 PM, Vic K2VCO wrote:

> Pete Smith wrote:
>> I'm thinking about following several people's advice and
>> direct-grounding the grids on my SB-220.  I'm told that this can
>> result in a bit more gain and enhanced stability.  Merits of the
>> procedure aside, if I do so, should I use copper strap of some sort,
>> or will large diameter copper wire be sufficient?  Should I ground
>> each grid pin directly to the adjacent chassis ground lug, or somehow
>> connect them to each other?  It appears that each ground connection
>> will only be about an inch long.
> Copper strap would have lower inductance and is what I've used in my
> homebrew amplifiers.  If you're going to bother changing it, might as
> well do it the best possible way.  I don't see what the benefit  
> would be
> from connecting them together; I'd just connect each pin to the  
> chassis
> with the shortest possible strap.

The shortest possible Cu strap has c. 15nH of L.  At the 3-500Z's  
grid resonace (c. 88MHz) this represents roughly pos. 9-ohms of X.   
The original 200pF cap used to ground the grid has c. neg. 8-ohms of  
X.  Will the resonant frequency by increased by the use the cap or  
the strap?

> -- 
> 73,
> Vic, K2VCO
> Fresno CA
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