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Re: Another "My First Coil" story.

Subject:  Re: Another "My First Coil" story.
  Date:   Tue, 27 May 1997 09:50:56 -0400 (EDT)
  From:   tesla-at-america-dot-com (Bob Schumann)
    To:   Tesla List <tesla-at-pupman-dot-com>


Phil,
      All the components sound like good choices to me! Getting
sparks at all in the beginning is a momentous accomplishment IMO.
True that the spark gap is not the best as you realize and have
stated. Make one of those Richard Quick cylindrical spark gaps.
I did and it made a world of difference for my system. 

Tuning is a trade off of capactiance and inductance.
In the primary circuit you have small L (primary coil)
and large C (primary capacitor). In the secondary circuit
you have small C (toroid or discharge terminal) and
large L (secondary coil). As the top of the secondary
gets bigger and you experimented with, the capacitance
of the secondary circuit gets larger and the resonant
frequency of the secondary with increase. To compensate
for this you have to tuner further out on the primary
coil which in reality is adding more L to the primary
circuit. There will be a point where your discharge
terminal will be to big for the power applied to
'break out' freely and you may have to force the
breakout using a pointed object like a pin, nail...etc.

If you want to be able to tune out further on your
primary (more L) you will have to give up some
capacitance (less C). Remove a plate or 2 from
your cap and retune. This may be messy since your
cap is already in the motor oil but I was wondering
if you assemble your plates 'under' the oil and are
careful, you virtually eliminate the chances of air
being trapped between plates.

Hope this helps some

Bob Schumann  






>Subject:      Another "My First Coil" story.
>       Date:  Mon, 26 May 1997 22:30:54 +1000
>       From:  Phil Chalk <philoc-at-ozemail-dot-com.au>
>Organization: Secure_Logic
>         To:  tesla-at-pupman-dot-com
>
>
>Greetings all,
>
>I've finally joined the ranks of those that've actually built one,
>throwing sparks !  But........
>
>Here's the details :
>
>(1) 12kV 30mA Neon Tx that's a bit 'sus'  It was given to me by the neon
>sign shop, so I figured it's  not perfect. The secondary measures
>(to CT, case) 8k from one end & 11k from the other.  However it makes an
>OK Jacob's Ladder & seems pretty much OK.
>   Chokes in each leg are about 400 turns #23, in 3 layers, well
>insulated, on a 10mm x 100mm (3/8" x 4") ferrite rod.  This was
>completely arbitrary - how are they ??
>
>(2) Cap is stacked plate;  Plates are 22cm x 17cm x .015mm (~ 8 5/8" x 6
>3/4" x .006") Aluminium 'Catering Foil'.  Dielectric is 20 x 100um
>(~ .004") sheets LDPE, i.e. .080"  26 plates (25 dielectrics) & approx
>8000pF. Drowned in 20W50 motor oil, & I don't have a vacuum pump, but so
>far so good.
>
>(3) Primary is 1/4" copper refrig. tubing in approx 30 degree spiral. 12
>1/2 turns till I ran out of Cu. Inner turn is ~5" dia. linear spacing is
>15mm (~ 5/8") Built on 5mm acrylic sheet base & supports.
>
>(4) Secondary is ~1020 turns of #24 SWG( ~#23AWG .56mm Cu., .63mm with
>insulation) Winding length is 25 1/2" close wound (~230m/250yd) on a
>70mm OD (2 3/4") acrylic tube, 3mm wall, sealed at both ends with
>acrylic disks, & coated with several coats of polyurethane. Brass plate
>as ground terminal, 1/4" bolt thru CB antenna base mount conical
>insulator, on top.
>    I can adjust the (vertical) position of the secondary such that the
>bottom turn can be between about 2" above to 6" below the plane of the
>bottom primary turn.
>
>(5) Spark gap is merely 2 x 3/8" bolts thru 2 bits of threaded 1/4"
>plate steel mounted on some 5mm acrylic sheet.  Wires soldered to
>the steel blocks.
>
>With nothing on the top terminal bolt it tunes at around turn 6, and
>throws several branching, violet, lightning-like sparks from the top of
>the bolt into the air, of maximum length perhaps 9-10". (and LOTS of
>NOISE !) It seems best with the secondary level or lower down inside the
>primary, than above. Seems best with gap = roughly .1"
>
>With a 6" copper sphere (toilet cistern float) on top, it tunes at about
>turn 7, and throws the odd spark from the centre rib - sometimes.  If I
>put a pin on the sphere it throws sparks from there, but no longer -
>perhaps shorter - than without the sphere. A roughly hemispherical spun
>aluminium 'wok lid' about 12" diameter throws many short (<= 1") sparks
>from the rim.
>
>I know the gap is bad - it was my first roughie from when I was dying to
>get it going.  I feel the secondary is probably too long.  I'd like more
>current than my 30mA (actively hunting transformers tomorrow!).  I now
>know that reducing the spacing of my primary turns will help - Thanx
>Gary Weaver.  I felt the coupling was inadequate, and was thinking of
>trying a cylindrical (solenoid) primary when I can, for comparison.  I
>think the cap is OK.
>
>I welcome anyone's comments on all the above, but the thing that puzzles
>me is that it seems to tune at relatively few turns for such a
>relatively long primary.  It is of course a thin primary.  Based purely
>on wire length, the secondary is a quarter wave at about 325kHz 
>I haven't done any maths about it yet, except to choose .008uF as the
>cap value, as its Xc at 50Hz is abot 400k, and I figure the effective
>impedance of a 12kV/30mA neon is about 400k.  Is this an uncommonly
>large value cap to use on this tranny ??
>
>Also why won't the sphere throw sparks into the air - too small ?,
>insufficient drive current ?  A torroid is on the "soon" list.
>
>So thanx for listening.  Any comments most welcome.
>
>Phil Chalk.
>
>
>