15 Dec
2011
15 Dec
'11
4:12 p.m.
>> IIRC mo purely linear system can produce
stable oscillations [...]
> On the one hand, that feels right.
> On the other, I'm considering an AGC circuit
that [...] uses a FET
> as a variable resistor, and trying to figure out where it's got
> anything nonlinear in it (assuming the amplifier is running class
> A).
I was using 'linear' in its mathemtical sense.
So was I.
It is clear form this that any aplifier iwth any form
of AGC is not
linear.
Right. What's puzzling me is where the nonlinearity comes from in the
FET-based version. I'm probably just missing something. (Does a FET,
modeled as a voltage-controlled resistor, count as nonlinear, assuming
it stays in the region where the model is reasonably accurate and
linear? Seems linear to me, but perhaps I'm missing something there
too.)
I am sure we all know the stroy of Fred Terman and a
certain
research student.
Doesn't sound familiar to me, for what that may be worth.
The name of this student was William Hewlett. The
product was the
model 200A audio oscillator.
Hm, I have some very old (steel case with, I think, brown speckle
finish, all-valve construction, land-anchor weight) HP electronics.
I should check model numbers; I might even have a 200A.
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