Rich said:
" With any tetrode, to obtain linear suds, one can vary the grid v. Or one
can vary the screen v. -- but Not at the same time. In other words, When
the grid potential varies, the screen potential must be fixed, and vice
versa. "
WHY NOT?
For a linear amplifier to result, the plate current simply must be linear to
grid drive. We know from the Eimac curves of the 8171 that gain changes
with screen voltage. Logic tells us that for any particular grid drive,
there must be a certain screen voltage that will yield the desired plate
current (to achieve linearity). That necessary screen voltage will vary
with drive, but can be plotted and will be a curve. If the G2DAF design
achieves the desired curve, then that condition of linearity will result.
Your statement is simply wrong.
There are a number of other factors that would remain, even if the original
G2DAF design satisfies this requirment of linearity. As has been brought up
before, the fluctuation of load on the driver may increase distortion and
could vary from exciter to exciter. But, that is what experimentation and
testing is all about. In fact, the grounded grid amplifier suffered from
the same problem - because the load is non-existent during 1/2 the cycle.
That problem was solved by using an input network to act as a flywheel. In
scientific investigation, it helps to understand the problem.
If any amplifier is to be rejected, it ought to be rejected for the right
reasons. This is called science.
Colin K7FM
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