Re: Air Caps

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: "Ed Phillips by way of Terry Fritz <twftesla-at-qwest-dot-net>" <evp-at-pacbell-dot-net>

Tesla list wrote:
> 
> Original poster: "Terry Fritz" <twftesla-at-qwest-dot-net>
> 
> Hi Cory,
> 
> Usually the capacitance value of air caps (few hundred pF)is too small to
> be useful.  Some people put them in oil to increase the value and add
> dielectric stength.
> 
> Cheers,
> 
>         Terry

	I have a capacitor using a multitude of regular air variables ganged
and driven in parallel, and stuck in an oil-filled lucite tank about 15"
square.  Maximum capacitance is about 0.02 ufd.  Haven't had any luck
with use in even a small TC because the breakdown voltage seems to be a
couple of kV.  The thing should be self-healing, but it isn't.  When
there's an arc the oil gets carbonized at some point between the thin
plates and can only be cleaned out by rotating the capacitors several
time and hoping the carbon will work its way out from between the
plates.  I can't complain, as someone gave it to me!  Heavy monster and
is holding down the floor in my attic.

	No doubt that a properly designed and built oil-filled parallel plate
capacitor would work just fine, and these were indeed used in "the early
days of wireless".  Expensive and difficult to build, and with MMC's so
cheap, why bother???

Ed

Ed