[AMPS] Is screen potential important?

[measures]

>
>Rich said:
>
>"In order to achieve linear amplification, current gain must be constant
>at All signal levels.  Screen potential has a large effect on current
>gain.  At 33% of normal screen volts, an 8171 exhibits 1/4 of normal
>current gain."
>
>Rich, you keep ignoring the fact that as the screen voltage varies in the
>G2DAF amplifier, the grid also varies.  

ok

>If they varied in proportion to each
>other, then I agree that the circuit would not be linear.  

indeed

>But the ratio of
>grid to screen voltage varies throughout the change in drive from 0 to
>maximum drive (because of the unique voltage doubler circuit).  

double trouble


>So, using your 8171 tube, if the screen voltage did not increase in 
proportion to the
>screen voltage, results could be linear.  That is what the debate is about.

 With any tetrode,  to obtain linear suds, one can vary the grid v. Or 
one can vary the screen v. -- but Not at the same time.    .  In other 
words, When the grid potential varies, the screen potential must be 
fixed, and vice versa.  
>
>The probem is that you keep hedging your bet by defining the rules so that
>your favored circuit will win by definition. ......
>to effectively ban them.
>
  What rule did I change?.   The reason I picked the 8171 is because 
Eimac published cc curves for E-screen = 33% of normal screen potential 
And E-screen =100% of normal.  This was ideal for showing the 4 to 1 
variation in anode current.    .  

later, Colin

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


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