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[Amps] Tube Class C operation no Drive power or grid current

To: Amplifiers <>
Subject: [Amps] Tube Class C operation no Drive power or grid current
From: "Fuqua, William L." <>
Date: Sat, 8 Oct 2022 18:37:40 +0000
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    Maybe I have not looked at the data sheets very closely , but I was 
surprised to find a medium power glass Pentode that required zero grid current, 
thus no drive power in class-C operation.  The 4E27, not the A version. 
Pre-Eimac version. Eimac countered with the 4E27A which had greater plate 
dissipation and did require some grid drive power and current.
   Also, looking at suppressor grrid modulation. Efficiency about same with 
control grid or screen grid modulation and class B AM linear operation.
Advantage is that the AF suppressor grid impedance is infinite because it is 
never driven positive. The downside is that high screen ggrid dissipation is 
That is because when suppressor grid is negative, current that would otherwise 
go to the plate is diverted to the screen grid.
   Just can't get something for nothing. Hi Hi Hi

Any other examples of zero control grid current glass tube class-C operation 
any of you have found.

Bill wa4lav

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