Re: [Amps] g-g amps

[R.Measures <r@somis.org>]

On Jan 9, 2005, at 4:28 PM, carl seyersdahl wrote:

>  Is there anything to be gained or lost when it comes to grounding the
> grid(s) directly as opposed to using chokes or (fuse) resistors.?? The 
> SB220
> measures grid current thru a .82 ohm resistor from cathode (fil) to 
> gnd , as
> opposed to the SB200 which measures grid current via the voltage drop 
> across
> a 1.5 ohm resistor in series with the bias supply/relay supply.!!!
>  I've often wondered about the reason for the different 
> approaches.(the 220
> uses chokes to gnd , vs the 200's 33 ohm resistors and capacitors to 
> gnd for
> RF.
>  Is one inherently better or safer than the other??

To find out which is better, try grounding only one of the three grid 
pins on a 3-500Z though a Cu strap, measure the grid-resonance freq., 
and repeat with one grid pin grounded through a 200pF capacitor.  When 
I did this test, the grid-resonance was pretty close to the same freq. 
either way, and roughly 20MHz lower in freq. than where 3-500Zs are 
known to be able to occasionally oscillate.   Thus, my guess is that 
there will not be much difference in VHF stability either way.  (note-- 
grounding more than one grid pin at a time will produce additional 
resonances between the pins that confuse the issue)
-  The safest way to DC-ground a grid is through an instrument-fuse or 
a frangible-R.

cheers, Carl

>     carl / kz5ca
>
>
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Richard L. Measures, AG6K, 805.386.3734.  www.somis.org

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