[AMPS] PA Recommendation Wanted

[Joe Subich, W8IK]

At 11:28 AM 6/8/97 -0700, you wrote:
>>Rich Measures wrote:

>Trying another door.........OK, I don't touch the screen V adjust.  
>However, what can can go wrong if one uses the grid bias V adjust to 
>adjust ZSAC in Class AB1? 
> The benefits of using the screen V adjust to set ZSAC are:
>1.  You wind up with the highest screen V--i.e., more RF output. (the 
>Esc^3/2 power law)
>2.  You don't run the nasty IMD risk of drawing grid current.  

However, by adjusting the screen voltage one changes the gain of the tube 
and risks excessive screen dissipation.  That is, screen voltage too low 
and stage ouptut is low with attendant overdrive and IBM ... screen voltage 
too high and the screen begins to act like the plate and show excessive 
dissipation.  

Design the grid circuit properly, including the PROPER input impedence 
matching, low Z (regulated) bias supply, and the proper drive level ... 
then the screen can operate at its design point. 

   ... Joe Subich, W8IK ex-AD8I
       <w8ik@ibm.net>



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