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[AMPS] Re: Drive Level in amplifiers

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Subject: [AMPS] Re: Drive Level in amplifiers
From: (Phil Clements)
Date: Tue, 24 Mar 1998 21:09:32 -0600
At 12:29 AM 3/25/98 -0000, you wrote:

>[Richard W. Ehrhorn]

>In class AB, B, and C power amps such as discussed here THE TUBES (or 
>transistors) ARE NOT LINEAR DEVICES. Plate current flows over much less 
>than 360 degrees of the rf cycle and is OFF the rest. The tube is as much a 
>switch as a linear device.

>IMHO the most fundamental way to define the function of the input matching 
>network of a class AB2 or B amp is that it (plus all the circuitry 
>intervening between it and the plate/collector/drain of the driver devices) 
>must transform the input impedance of the power tube(s) into whatever load 
>impedance those driver devices must see to deliver their desired output. 
>Alternately, since nearly all transceivers are designed to work best into a 
>nominal 50 ohm resistive load, the power amplifier input network should 
>present a 50 ohm resistive input.

And this is a trade-off between the need for a Rs that will allow the maximum
transfer of power over an entire band while providing the needed fly wheel
(Trading a little Q for a little bandwidth and a fly wheel)
The RL is complex and  ever changing with the input waveform. I think a
lot of folks are trying to equate the tube RL to an antenna or constant
resistive load. Bad assumption...

>During preparation of the amps chapter of the 1995 ARRL Handbook I included 
>this argument, but the issue apparently had been so controversial that 
>League diplomats thought it best to forgo that discussion. Probably I'll do 
>the same hereafter!

You are lucky, Dick! You could have been impaled upon the Woof Hong stick,
or burned at the stake for suggesting such far-out witchcraft!

Your presence and expertise are very much appreciated here on the Reflector
Dick. Please stick around! At least freedom of the press still prevails here.


Phil, K5PC

"To do is to be".....Sartre
"To be is to do".....Aristotle
"To be or not to be".Shakespeare
"Do be do be do".....Sinatra

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