[AMPS] Is screen potential important?

[measures]

>Rich says:
>
>>The basic problem is that there was no way to keep the screen bypass
>>capacitor adequately charged during voice modulation
>
>I don't understand. It appears to me that when there is a signal, there are
>screen volts. 

Not until the screen bypass C becomes sufficiently charged.  Another 
problem is keeping the screen bypass C from mostly discharging on soft 
syllables.  The semi-obvious solution is to Not Allow the screen bypass C 
to discharge as long as the amplifier is in operation.  This is where 
Thornley seemingly derailed

> If it's a big signal, there's lots of screen volts, which you
>need because you wants lots of plate current. If it's a small signal, the
>peak plate current is less, so you don't need as many screen volts. 

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.  

> So it
>appears that screen time constant should be short enough to follow the
>envelope of the signal - which in the original, it was.
>
The result will undoubtedly be varying gain.  
>
later, Peter

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


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