RE: Questions.

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

Original poster: "Lau, Gary by way of Terry Fritz <twftesla-at-uswest-dot-net>" <Gary.Lau-at-compaq-dot-com>

Comments interspersed:

>Original poster: "Joshua H Ball by way of Terry Fritz
<twftesla-at-uswest-dot-net>" <jhmball-at-juno-dot-com>
>
>Hello list.
>I've been on the list for a while and am looking to build a my first coil
> in the near future. I have a few questions:

>1.  What should be a good target frequency for a coil?  What are the
>pro's and con's of a higher or lower frequency?  What effect does the
>input ac's frequency have?

A lower resonant frequency is generally believed to be better as some of the
loss mechanisms (i.e. skin effect in conductors) are less at lower
frequencies.  But it's difficult to say for sure since it's impossible to
change only the frequency but keep everything else constant.  The AC line
frequency is not really significant.

>2.  I have found some caps I can get for a relatively good price and
>would like to use them for my coil.  Are these in the right ballpark for
>tesla coils?
>	  .001 UF 10 KV AXIAL CERAMIC DISC CAPACITOR   $ 1.00 each

Ceramic caps are not very good for a tank capacitor.  Their dielectric
losses are high and their capacitance will change significantly with
temperature, detuning the resonant tank circuit as they heat up.  The caps
you describe would be good for use in an R-C NST protection circuit (if
seriesed 2 or 3 to get a high enough voltage).

>3.  When demonstrating a coil indoors what do you use for a ground?  Do
>you simply run a wire to outside?

It depends on the size of the coil.  It it's a truly small one (like you can
lift it with one hand), you can get away with a much less robust ground,
maybe even tie it to the AC 3rd wire ground.  But for anything else, yes,
run a wire to a real independent ground.  The reasons are more to do with
minimizing potential damage to household appliances than with increasing
spark length.

>4.  Wouldn't a conical secondary be more efficient than a cylindrical
>one?  One reason being that the magnetic force from the lower wider part
>of the secondary coil would create a higher voltage on the smaller higher
>part.  Know what i'm saying?

Efficiency really doesn't enter into it, as the losses in the secondary are
not all that significant.  A conical secondary may give a higher coupling
coefficient k, but the same k could also be achieved by lowering a
conventional cylindrical secondary just a bit further towards the primary.
And the problems associated with finding a suitable conical form and winding
it just don't seem worth the trouble, since there's no evidence that a
conical form is in any way superior.

Regards, Gary Lau
Waltham, MA USA