SV: SV: [AMPS] Final..

[George T. Daughters]

Rich wrote...

> > I do not agree.  In AB1, the grid looks like a capacitor.  
> > 

To which John replied...

> Now you got me!!!!!   How the hell can one develop power into a pure reactance?????
> Surely the grid of a tube biased for AB1 is resistive?

My understanding is that one DOES NOT deliver power to the grid of an 
AB1 amplifier.  The driving voltage is always such that the grid 
is never driven into the region where grid current flows.  All one 
does is charge and discharge the "input capacitance" of the tube.  
If one refers to one of the ARRL handbooks, in the tube 
charactersitics section, one finds "driving power = 0".  

So the grid of a tube biased for AB1 is NOT resistive.  A good way to 
make the input of such an amplifier appear as a constant resistive 
load to the exciter (a good thing!) is to put a fixed non-inductive 
resistor from the grid to (RF) ground.  The resistor dissipates 
(wastes!) the drive power.  Another benefit of such a resistor is 
that it enhances the stability of the amplifier.

73,
 
George T. Daughters, K6GT

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