Re: Coil ratio; width versus length.

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

Original poster: "Barton B. Anderson by way of Terry Fritz <twftesla-at-qwest-dot-net>" <tesla123-at-pacbell-dot-net>

Hi Edwin,

A smaller aspect ratio might help, but I personally haven't gone beyond
4.8. JavaTC showed 36" for
your coil. This is an optimum value. It also showed tuning at 12.6 turns.
You mentioned being tuned
at "3.5 turns in". I assume this is equivalent to 12.5 turns. Also shows
coupling K at 0.15. To be
accurate, we would need to know the OD at the tap point, not the far end of
the full primary. Have
you adjusted coupling ? Because the coil has a high number of turns
(~1,460), the volts/turn will
be low. You might be able to benefit from a higher coupling which will
induce more current into the
secondary. You want to try to get the highest couling with the least
trouble. You may have already
gone through this, but thought I should mention it. Typically, the
secondary is lowered in
increments until problems like racing arcs start and then raised up in
small increments until they
stop (everyone has their favorite method, but thats the basic idea).

Take care,
Bart

Tesla list wrote:

> Original poster: "Edwin G. Buttell by way of Terry Fritz
<twftesla-at-qwest-dot-net>" <edd.b-at-snet-dot-net>
>
> Edd.B Writes
>
>    I have a question for the list;
>
>    I converted my old tube coil to a spark gap coil
>    and the secondary does not conform to the "standard"
>    1:4 or 1:5 rule.
>
>    Perhaps some info on the coil will help.
>
>    Primary: inverted cone, 6.25"I.D. by 26"O.D.
>    at a 45 deg angle, 16 turns of 3/8" copper tubing.
>    Tapped at 3.5 turns in.
>
>    Secondary: 4.5" dia 43" high, winding length is
>    approximately 36.5" using 23ga enamel wire with
>    the last several turns spiraling up to a 3"
>    porcelain standoff terminal. No toroid is used.
>    ( yet )
>
>    NST. 15kv 30ma with 122mfd pf correction.
>    secondary protection, safety gap, choke coils,
>    two 250pf caps to gnd (case).
>
>    Spark gap. 7 segment 3/4" copper couplings end
>    to end with forced air cooling. A 5" blower at
>    3450 rpm forces the air through the couplings.
>
>    Primary cap. Geek caps, .01uf (longest discharge)
>
>    The streamer length is around 20" or so from the
>    top of the standoff. The streamers are very steady
>    and bright and quite loud.
>
>    Getting back to the question,,, The coil L x W ratio
>    is around 1:8.5. Should I cut the coil down to the
>    preferred ratio of 1:4 or so ?????????
>
>    I think the coil should produce 30" to 36" streamers
>    when it finally completed, is that possible with a
>    secondary that is too long ?????.
>
>    Thanks for the help.
>    73's de Edd.B.