Re: [TCML] Tuning a new coil

["DC Cox" <resonance@xxxxxxxxxxxx>]

For optimum performance with a 12 kV 60 mA nst you might consider rewinding
your sec coil with 28 AWG wire.  Mine, wound with #28 heavy build,  puts out
36" long sparks on a 12/60.  4.3" od sec x 22" winding length.  12 x 3 "
toroid.

Send me an email off-list and I will email you some photos of it in
operation.

Dr. Resonance

On Sat, May 17, 2008 at 7:51 AM, b alex pettit jr <a_pettit_jr@xxxxxxxxx>
wrote:

> Sorry !
>  Without Attachments ...
>
>
>
> Hi All,
>
> Thanks for the details.
>
>
>
> I agree, the ResFreq should  be closer to 295. The coil dia is 4.5",
>
> and wire resistance is a total of 29.7 ohms. I did a quick turn count
>
> and it is right at 44 TPI.
>
>
>
> I will check this HP 5315B counter agains the scope today. It would
>
> be ideal to have the JAVATC model match the hardware.
>
>
>
> As I said, I built many TCs over the decades-  most not
>
> too impressive in their performance. My last venture was
>
> in the 1980s in duplicating one from a book of the 1915 era.
>
> With stained and varnished wooden cases for the   transformer,
>
> glass plate cap, rotary spark gap and coil base, it looks
>
> quite authentic for that time.
>
> It is not an optimal design, but I'd rather leave it for its
>
> antique appearance and build another.
>
> The referenced coil has an 8" dia tube, 16" long and wound with
>
> string spaced enameled wire. It gives ~ 12" sparks.
>
>
>
>
>
> SO, I am excited about this coil performing a bit more impressively !
>
>
>
> Bart, from your JAVATC 'demo' it appears you overdrive your
>
> NST to 140 volts. I was considering this - is that ok ?
>
> Will it gain me anything if I do not increase   the pri cap
>
> from 0.0188 to 0.0199 uF as specified ? A wider spark gap
>
> would be easy.
>
>
>
> Thanks again for the guidance,
>
> Alex P
>
>
>
> PS:
>
> I just retired from industry and began teaching a senior
>
> college level mechanical eng course and lab in mechanical
>
> dynamics, vibration and modal analysis.
>
> The parallel between that and these electrical systems is AMAZING !
>
> ********************************************************
>
>
>
>
>
>
>
> Hi Alex,
> I'm showing your coil should be nearer to 295 kHz. Your 323 kHz seems a
> little high to me. I know it's a small amount, but in this configuration,
> Javatc is always much closer. Usually in situations like this, the inputs to
> Javatc are not exact. For example, secondary is slightly smaller than stated
> (like 4.25") or things of that nature. Turns affect this also, but your 920
> turn count seems about right and the secondary diameter would affect this
> frequency quite a bit (20 kHz just for a 1/4" difference in diameter).
>
> On the primary side, cap tolerance will affect how much primary is needed
> as well as the primary itself. Good to measure the cap to be sure of it's
> total C. In any case, 1 full turn will affect about 44 kHz on the primary
> side for your coil. Thus, if the tuning is close to begin with, the ideal
> tap will be within inches. I suspect your coil will perform well at about
> turn 6.
>
> When you tune the coil in at low power, you also get small sparks. As you
> increase power, spark lengths increase. Those sparks add a small amount of
> loading changing the frequency of the secondary slightly. So, a small amount
> of increased inductance is often added to match streamer loading. Say your
> coil tunes in at low power at 5.6 turns. When full power is applied (and if
> good streamers are forming), you may want to increase the inductance a few
> inches (but that is something you have to play with).
> Take care,  Bart
>
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>
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