RE: Capacitors

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

Original poster: "Richard Wayne Wall by way of Terry Fritz <twftesla-at-qwest-dot-net>" <rwall-at-ix-dot-netcom-dot-com>

John,

Your idea is very sound.  You could also put multiple tubes of different
radii together coaxially for greater capacitance.  Capacitive tuning really
comes into it's own in situations where there is no real inductive tuning
of the primary -- such as the OLTC where there is only a single primary
turn.  A ball park primary capacitance can be selected with MMCs then fine
tuned with your variable capacitor.

Air, and even better yet oil, dielectrics are self healing and make good
variable capacitors.  About five years ago I obtained a couple of large air
multi plate variable capacitors from old transmitters.  By changing the
spacers between the plates to thinner ones I increased the capacitance
significantly.  I then put the whole thing in oil which increased
capacitance even more.  It worked fine for tuning a small TC.  I believe I
posted on it to this list.

Keep up the original thoughts and let us know how it works out.

RWW

  
> Two brass or copper tubes, one slightly smaller than the other, so that
one has
> the ability to slide in and out of the larger one.  Over the smaller of
the
> tubes, a dielectric of some type, maybe super thin walled lexan(?)  One
of the
> tubes would remain stationary, and plastic all-thread would be attached
to the
> mobile portion via an end cap with corresponding threads, so that as the
rod is
> turned the one "plate" is allowed to move within the other.  The whole
assembly
> could be oil immersed, with the "crank" coming out of the top of the
container
> to eliminate sealing problems (as opposed to exiting on the container
side). 
> What would the efficiency of a design such as this be?  What are the
> possibilities of finding a decent dielectric, and how thick would it need
to