Rich said:
"The bottom-line with with the DAF design, is that it is possible to have
virtually any screen potential at the grid v peak. . . The grid v varies
at an RF rate but the screen v does not - and none of the DAF enthusiasts
appear to have even given it a thought."
Rich, you are wrong. This point has been discussed numerous times, but you
have ignored it. You keep citing the results of your friend Norm, who stuck
a 1 mf cap on the screen.
The screen must follow the grid voltage, more or less. Note that the
original design used a minimum capacitance - which removes the rf from the
screen - but no more. Screen voltage must follow the control grid. The
control grid will not follow the input perfectly, as there will always be
some delay in signals arriving at the control grid. Ideally, the screen
voltage must follow the control grid voltage precisely. But, there is no
perfect amplifier. None of your amplifiers are perfect. The real question,
for the G2DAF amplifier, or any derivative, is how linear is it in practice.
More particularly, how much does it splatter? The bastard amplifier built
by Norm does not count. And, the fact that you have heard bad examples
does not prove that good examples do not or cannot exist.
My testing of varying screen voltage and grid voltage on an rf amplifier at
varying rates indicates that it may be sufficient for the screen voltage to
be able to follow the grid voltage at an audio rate, rather than an rf rate.
Finally, you keep citing the 3/2 power law as proof that the G2DAF amplifier
must distort badly. A few months ago I cited the definition from Eimac.
Under their definition, there is no violation of the 3/2 power law. But, I
have never heard your definition. Please define your version of the 3/2
power law and what is violated by the G2DAF amplifier and how that causes
distortion.
Colin K7FM
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