[sdiy] tubes, MOVs, etc.

[Grant Richter]

> While we're on this "off" topic, here's a website where the guy writes about
> several related topics, including what he calls "solid state tube" amps of
> his own design. He has tube amp circuits and more.

I have been going through old electronics books in the library looking for
fresh ideas. There are a lot of good ideas that were proposed but never
acted on.

Anyway, the early British books refer to transistors as "crystal valves".
Quite charming.

Found a real interesting book on using "voltage dependent resistors" (MOVs)
for non-linear function generation. Never saw that before. Basically, you
use an MOV for the input resistor to an op-amp, because it is non-linear, it
gives a non-linear output function. Then if you put another one in the
feedback loop, you get all kinds of wacky functions.

The soft response curve of the MOV is used to replace multiple breakpoint
diodes with hard thresholds for a continuous smooth function with low parts
count.

I'm sorry, the book doesn't call it an op-amp, it's a "two port voltage
amplifier with feedback".