Re: New coil

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

Original poster: "Dr. Resonance" <resonance-at-jvlnet-dot-com> 


Always start with a "scrap wire" primary --- usually some old 12 AWG house
wiring works fine.  Use 20 to 26 turns max so you can find your exact tuning
point before putting the copper tubing in place.  This scrap wire pri has a
bare turn scraped every turn and staggered slightly so they don't arc over.

Keep your total pri spark gap at 0.120 inch maximum while doing initial
tuning.  Also, never increase your variac beyond 35-40% max until all tuning
is finished.

This tuning should also include raising your sec coil in 1/2 inch increments
to find the best coeff. of coupling match.  This is easy to do.  Use a small
piece of brass attached to the underside of your upper sub-base.  This brass
is drilled and tapped 1/4-20 NC.  Make a long 5 inch 1/4 brass stud coming
out of the bottom of your sec coil.  Then you can just screw the sec up and
down until you find the sweet spot.  Later, cut off the excess brass stud on
your sec coil.

After all this is done you can bring your variac up to full power --- never
before.

It sounds like your NST and pri cap might be resonating --- in which case it
can build up a resonance equal to 2.22 x Erms of the NST.  Be careful as
this can blow xmfr and caps.

A good value for cap would be equal to 1.6 x resonant value for your xmfr.
See the Geek Group charts to find the resonant value for your particular NST
and then use 1.6 x that value.  This insures your xmfr will not be in
resonance with your cap.

Resonant value does assure max power transfer, but NSTs are not made to
withstand the resonance and will blow.  This also applies to MMC type caps.
Set your MMC for approx 2.5 x Erms of the NSTs potential and you will not
have overvoltage problems.

Dr. Resonance

 >
 > Well, last night I fired up my new 4.5" coil, and
 > performance was great for a first fire, but I do have a few questions and
 > comments for the list.  Here's the specs:
 >
 > Secondary:  4.5" OD PVC with 36" of heavy build #24.  Set 1" above
primary,
 > last winding 3" from top of form.  Total pvc length 42".
 >
 > Primary:  14 1/4 turns of .25 Cu tubing.
 >
 > Toroid:  Quick lash up of 4" dryer duct.  24" by 4".
 >
 > Gap and cap bank:  8 942 CD's in series mounted next to a five segment
 > copper pipe gap blown with a small muffin fan.  Everything mounted on two
 > sandwiched 8 by 11 cutting boards.
 >
 > Transformer: Transco 12/60.
 >
 > Upon first fire up, I tapped at turn 14 1/4, as I usually start from the
 > outside in when first firing.  This happens to be the number of turns I
 > wound up with before running out of a full roll of tubing.  Instant
multiple
 > streamers, maybe four or five at a time, with the longest consistently
 > hitting the 36" mark.  Within a minute or so, a capacitor lead arced to
the
 > muffin fan, killing it.  I set up another fan, and proceeded.  Within
 > another minute, I heard a sound like a rifle shot every 15 seconds or so.
 > Turns out the last capacitor in the bank was arcing to a bolt which joins
 > this same cap to a lead to the primary.  The arc had to jump over an inch,
 > and I figured that since both the last capacitor and the wire going to the
 > primary SHOULD be at the same potential, I wouldn't have a problem.  Why
did
 > this happen?  Even though there is a hole in this cap, there was no loss
in
 > performance.  I am obviously going to need a larger topload, and was
 > thinking of going to a 6x30 for the final configuration, judging from the
 > length and amount of streamers I presently have.  Do you guys think I
should
 > add a few more turns to the primary, taking into consideration the larger
 > topload and future dedicated 15/60 NST?
 >
 > A few comments on the physical design of this unit.  The whole primary
base,
 > including the primary supports, are made out of plywood, so to those who
 > feel that HDPE or similar is required, don't be afraid to work with wood
if
 > that's all you have.
 > Remember to keep lots of spacing between components, or you will have
arcing
 > problems like I had above.  Also, don't bend the tubing unnecessarily, or
it
 > becomes very hard, and you will set new records for profanity.  For those
 > who are wondering how to anchor threaded rods for screwing on the topload
 > and the bottom to your base, try what I do:  Cut two wooden discs that
will
 > fit snugly into your form.  Epoxy the first one in about two and a half
 > inches below the end of the form.  Drill a centered hole in your other
disc,
 > and four or five random holes along its perimeter.  Mix up a batch of
 > fiberglass resin, and pour it over the first disc.  Place a length of
 > threaded rod thru the center hole of the last disc, and anchor with nuts
on
 > both sides.  Slowly push it down into the form until the resin starts to
 > squeeze up thru the outer holes.  The disc should now be about a half inch
 > from the end of the form.  Thread the winding thru a small hole in the
form,
 > and anchor with another nut.  Finish off by filling the remainder of the
 > space with more resin, submerging the wire and last nut.  Both ends
 > shouldn't take more than fifteen minutes total, excluding resin drying
time.
 >
 >
 >