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A down and dirty coil
Today was fun!
I wanted to see, if I could make a coil in a day, so I hauled out a
secondary that was really intended for a tube coil, 4" by 16" 25 gauge
wire for 820 turns, 15 mH and 7 pF. With one of John Freau`s small 1.5
by 6 toroids on top, the extra 6.6 pF lowered the res freq. to 345 KHz.
The primary was made from 1" wide, 0.03" thich phosphor bronze strap,
which I wound into a spiral, with 1/4" thich wire inbetween, to keep the
strap spaced, and taped outside to keep the coil in shape. Then I
smeared some Plastic Padding Cemical Metal on a sheet og G10, and sat
the coil in it. 10 Minutes later I could remove the wire, and the tape,
and woila: a nice, flat strap primary.
Mounted the secondary with 3 nylon screws trough the G10, the coil form
is HDPE pressure tubing, so it is thick enough to take a 4 mm thread.
The primary coil is on the other side as the secondary.
Capacitor is a MMC type, 4 atrings with 4 each 56 nF , 1600VDC Phillips
386 pulse caps. 33Mohm resistors in parallel of each cap.
The spark-gap is 2pcs. 1" by 4" copper tubes screwed to a piece of
tufnol, in the one end. They are not parallel, they taper away from each
other in the other end. The middle electrode is a similar copper tube,
standing on end, inbetween the other 2. This way, due to the taper
between the 2 fixed electrodes, adjusting the gap is very easy, just
push the center tube further out from the narrow end. The center tube
heats really quick, so it is good to have some extra to set aside for
cooling.
The transformer is 2 MOT`s in series, with a ballasting inductor in
series. I think it is 63 mH.
My registered copy of Wintesla (hint, hint!) told me that I should tap
at 3.8 turns, so without further adoo, I did that, and cranked up the
variac.
The cutest little streamers shot out in the air! With a bit of tweaking,
I managed a nice 12" to a grounded rod, invited my Wife and Daughter
down into the basement to see this cute little coil in action, and
decided to call it a day.
The lesson that I wanted to learn today was, how will just 2 MOT`s
perform in tesla service?. I`d venture to say, not bad at all.
This was a really satisfying Tesla experience, because this is only my
second coil, and it is small, but it doesn`t really matter because small
streamers are loveable too.
Cheers, Finn Hammer