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Re: Small Coil Questions

Tesla List wrote:
> 
> Subscriber: Esondrmn-at-aol-dot-com Fri Jan  3 21:54:09 1997
> Date: Fri, 3 Jan 1997 13:48:23 -0500
> From: Esondrmn-at-aol-dot-com
> To: tesla-at-pupman-dot-com
> Subject: Small Coil Questions
> 
> I have a couple of questions about my new small coil.  Again, it is 3.0" dia
> x 13.0" winding length - about 917 turns of #28 wire wound on acrylic form.
>  Primary is flat, 14 turns of #10 solid copper wire.  Spark gap is the
> standard cylindrical with 6 gaps of .028.  Power is one 12 kv 30 ma neon.
> 
> I am only getting about 11.0" of spark to a grounded wire.  Is this less than
> it should be?
> 
> On the safety gaps, I have them set to .34" on each side with a grounded
> contact in the center.  They fire very regularly at this distance.  I would
> like to open them up some more so they only fire infrequently.  Am I likely
> to damage the transformer?  I have a 3,000 ohm resistor and a 1 mh choke in
> series with each H.V. lead from the transformer.  On my larger 6.0" coil
> fired with a 14.4 kv pole pig, I have the safety gaps set at .50" on each
> side and they seldom fire.
> 
> Another question is tuning and Q.  This is a very clean construction with all
> acrylic materials, rolled poly cap, etc.  I expected the tune to be very
> sharp but in actuality it doesn't seem to be.  The best tune is 13 turns,
> which is about what I calculate.  Turn 13 is defintlely better than turn 12
> or 14  but I can't really tell much difference between say turn 12.5 and
> 13.5.  Is this normal??  I have the same problem with the 6.0" dia coil.
> 
> Thanks,  Ed Sonderman

Ed,

The Q of this smaller coil is dominated by your secondary - the fine
wire size is adding substantial DC and AC resistance. The impact is
reduced Q, and wider tuning "bandwidth". The same holds, to a lesser
extent, for the primary, since the relatively small wire diameter adds
significant AC resistance. Re: your safety gap - there's only one sure
way to tell. :^)
At some point your safety gap will no longer behave as one. You may want
to increase the choke inductance though, 1mH is a little low. 10 mH
would be better, and 100 mH would be great!

Safe coilin' to you, Ed!

-- Bert --