Re: transformerless TCs/ would a variometer be useful?

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

Original poster: "Antonio Carlos M. de Queiroz by way of Terry Fritz <twftesla-at-qwest-dot-net>" <acmq-at-compuland-dot-com.br>

Tesla list wrote:
 
> Original poster: "Jolyon Vater Cox by way of Terry Fritz
<twftesla-at-qwest-dot-net>" <jolyon-at-vatercox.freeserve.co.uk>
 
> With regard to transformerless/ capacitive transformer Tesla coils, I cannot
> help but think that where C1 is to be substituted for larger/smaller
> capacitance it would be useful for L1 to be variable to facilitate
re-tuning in
> a similar to adjusting the primary tapping point on a conventional TC.

Certainly, and it would be better if L1 could be adjusted while the coil
is working.

> Does this not sound similar to adjusting the impedance match of an
antenna to a
> radio transmitter using an Antenna Matching Unit- except that with an AMU the
> coils are largely fixed and fine tuning is done by a variable capacitor
whereas
> with a Tesla coil the reverse is usually the case.

Ok, due to the lower operating frequency, the capacitors are too big to
be tuned (except for the terminal capacitance, where a telescopic
antenna
works very well).
 
> In view of this and the fineness of tuning (does tuning on have to be this
> fine?) would not the variometer-type of variable inductor be the best design
> for L1 in a transformerless TC?

Yes. And for use as "off-axis" inductance in series with the primary of
a
Tesla transformer too.
The tuning becomes fine in the low-coupling modes, that correspond to 
higher voltage gain in a directly coupled system, but it's not so 
critical.
 
> If the above is correct, does anyone have a design for a cheap, reliable
> variometer, all the better if it were a small one- given the "miniature"
nature
> of my anticipated design
> -L2 is only 5 5/16" tall and 1 1/8" in diameter and the final TC will
> (hopefully!) be driven by no more than a flyback transformer.

Maybe two coils, one fixed and other that can be rotated, interconnected
in series (or in parallel) by flexible wires. In the simplest design
just
make two coils, place them over a thick insulating plate (as I did in my
setup), and move one of them to tune. 

Antonio Carlos M. de Queiroz