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Re: non-linear capacitance (was doorknob caps)
[snip]
> A
> friend and I had a pile of such caps and they seemed to work
> just fine for a couple of minutes and then the system they
> were in started to behave like a high value resistor had been
> introduced in the transmission line from the cap to the primary.
> The secondary behaved as though it were oscillating in several
> different modes and arcing to itself all the way up and down
> its' length.
> It turned out that several of the caps were changing
> capacitance under load, by as much as 40%. When they cooled
> down they recovered the original value.
> Perhaps they were leaking? Developing high resistance
> paths internally that faded when they cooled. I don't know.
> I haven't seen anything like it before or since.
[more snip]
>
> John
Most doorknob caps are barium titanate, sometimes alloyed with strontium and
other dielectric materials. These materials are non-linear dielectrics,
i.e., their capacitance can change value drastically with temperature and
even with voltage. For coiling purposes, this change in capacitance value
is a real nuisance. In the 1950's the Navy used this non-linear effect to
design and build the world's first dielectric amplifiers! Solid state,
impervious to electrostatic voltages, dielectric amplifiers were an
excellent alternative to vacuum tubes which would implode in submarine
application. I think it would be a fascinating project to design and build
a dielectric amplifier driven Tesla coil - rather like a vacuum tube driven
coil, sans the vacuum tube. Very efficient and probably impossible to blow
up. I will put copies of some old 1950's vintage articles up on my web page
tonight on dielectric amplifiers, if anyone is interested, check out my
Tesla coil section at http://users.ticnet-dot-com/bertpool
Bert Pool