On Sun, 03 Oct 1999 14:42:46 -0600 Tesla List <tesla-at-pupman-dot-com> writes:
> Original Poster: Norman Hockler <norsan-at-bright-dot-net> 
> Hi Gang...
> Would like to build a coil and I have a few questions.
> 1.  I have a cap rated at 1 uf  -at- 25kv.  cap says its DC but there 
> is no 
> polarity marking on the cap.  can I use it ???

1uF is really too high for a tesla tank cap. Normal values range around a
few hundreths of a microfarad. For instance, my coil uses .014uF at
resonance with a 12Kv 60ma NST.

> 2. I have seen pictures of the primary coil wound  vertical, 
> horizontal  and conical...what are the differences in results.

generally, but not always true, flat spiral primaries provide minimal
coupling for a coil and help avoid pri-sec strikes, vertical (helical)
spiral primaries will give the most coupling, but may induce pri-sec
corona or strikes and so is usually only used at lower power levels, and
the conical primaries are a compromise between the two. There seems to be
little convention in choosing what style to build, aside from helical
coils being favored for small systems (ease of construction), and flat
coils helping to reduce the possibility of pri-sec strikes from large
systems giving discharges longer than the sec. length. 

But as I said, the advantages/disadvantages of each design a really not
that much different from each other, so the choice is really up to the
coiler. I've used helical coils on my small systems since they are easy
to build, and am using a big 17 5/6 turn flat spiral coil for my current

> 3. I have a small dc motor that I can control the speed ....I am 
> thinking 
> of using it to power a Rotary spark gap.  Cant I tune the primary by 
> changing the speed of the motor??

No, if you mean the frequency the whole thing will oscillate at. You can
vary the rate at which the gap breaks down, but not the actual resonant
frequency, which is determined by the capacitance and pri inductance (to
put it simply, and within my ken ;). The oscillations of the primary
system occur when the gap is in conduction, that is, during the time
after the spark has been struck and and when the energy either "dies out"
or the spark is extinguished by other means. (like the moving electrodes
of a rotary gap)

Remember that non AC-synchronous rotary gaps will generally kill NSTs,
though AC synchronous ones will work great. If you would like info on how
to convert a normal induction  motor to a salient-pole induction motor,
and thus AC synchronous, reply on or off list, and I (and lots of other
people, probably) would be glad to tell you how. All you really need is a
file, patience, and ambition.

> Appreciate your responses.
> Norm

Hope I was of some help,

Grayson Dietrich,
"The Electrophile"

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