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[AMPS] More Plus: Drive derived screen voltage

To: <amps@contesting.com>
Subject: [AMPS] More Plus: Drive derived screen voltage
From: measures@vcnet.com (measures)
Date: Tue, 21 Dec 1999 03:11:14 -0700
>..........
>
>........ The Care and Feeding of Power Grid Tubes that the screen
>voltage was constant. (Rich might say that they never thought anyone would
>be so stupid as to vary the screen voltage - making the test pointless).

?  "shit happens"  --  Forrest Gump.  

>However, they do have an interesting comment in 4.4.4  (Effects of Screen
>Voltage)  "... Usually, the lowest value of d.c. screen voltage compatible
>with a given power output will produce the lowest intermodulation
>distortion."  

?  As I see it, this means something different.  To wit:  when the screen 
voltage is adjusted too high for the available drive available in AB1, 
ZSAC increases unnecessarily.  .  To put the ZSAC right, one then needs 
to increase grid bias beyond normal.  This results in moving the 
amplifier even farther away from the AB1 target of peak grid potential = 
0v.  In other words, the best way to adjust a class AB1 amplifier is to 
adjust the grid-bias for virtually zero grid current - and then keep your 
paws off.    Screen potential is used to set ZSAC.  However, the max. 
screen potential rating should not be exceeded.  .  
>........

-  Rich..., 805.386.3734, www.vcnet.com/measures.  


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