[AMPS] Re: New G2DAF amplifier information

[Peter Chadwick]

Rich says:

>My guess is that he is not all that familar with constant current curves.

Constant current curves are not necessary to design amplifiers. They are
only another way to present the transfer characteristic of the active
device. The RCA transmitting tube handbook shows how design from usual Ip/Vp
curves (with Vg as a parameter). I submit Rich, that Pappenfus et al really
do know about the subject - and did so 40 years ago.

	>>Not necessarily so. It depend on the relative ratio of grid
swamping to non
	>>linear grid current loading. 

	>Tossing off the effect of rapidly decreasing grid resistance as
grid 
	>current flows does not wash. .    

So the input impedance gets so low? If I have a 12.5 ohm swamping resistor,
and the grid current is 100mA at 50volts pk, I have 4 amps peak in the
swamping resistor, and 100mA in the grid. Hardly a noticeable change. 


	>>   Additionally, you appear to assume that the
	>>input impedance of grounded cathode AB1 stage is constant and
high.  

> [chortle] 
> 
Does this suggest that you don't assume that?

	>>This is not necessarily so - because of Miller effect.
	>>If the driver has adequte NFB to reduce its output impedance, the
effects
> >>are minimised.
> >
	>I know of no commercial radio that works well with other than a
50-ohm 
	>load.

How about KWM2, 32S1, TR4, T4X, SB101, FT101, FT102, TS850 etc.............
all of which can manage a 2:1 SWR? 

If you were to say that 'In general, in amateur service, operation of a
grounded cathode stage with grid current is undesirable because of
intermodulation difficulties', I'd agree. But your sweeping generalisation
that 'grid current causes splatter' is not always so, and there is a vast
amount of professional literature to prove that point.

73

Peter G3RZP


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