16 Dec
2011
16 Dec
'11
2:22 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.) 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.