Christmas Coil Saga
A Christmas Story for Coilers
by Fr. Tom McGahee
The story begins innocently enough...
Meanwhile, out in the garage,Bill the ********** was
busily lashing together his latest concoction: In
keeping with the Christmas Spirit, Bill was building
a rather large Christmas Decoration for the front
yard. To the uninitiated it looked simply like a large
aluminum Christmas tree mounted on a pedestal of some
sort. In reality, the aluminum Christmas tree was
merely the Topload on Bill's latest Tesla Coil. Bill
knew full well that the geometry of the tree did not
really lend itself well to being an EFFICICIENT
topload. But that was all-right. Bill was more
interested in shock value than he was in efficiency.
Actually, the pedestal was the "extra" coil of Bill's
experimental Magnifier Tesla Coil. According to his
calculations the "extra" coil should be capable
of throwing arcs at least 6 feet long.
He chuckled to himself as he struggled to move the
"extra" coil and Christmas tree topload out of the
garage and onto the front lawn. His wife was currently
curled up in front of the fireplace with a book and two
cats. Bill hated cats, but for the sake of his wife
he tolerated their presence in his home. Bill strapped
the coil/tree assembly to the top of the little
American Flyer sled, and wrestled it into position on
the front lawn. The final position was about 7 feet
away from the shoveled walkway that led from the
street to his front door. Bill always used the side
door, but he had In-Laws coming over tonight, and
*they* always used the Front Door. He figured the
6 foot arcs would be hurled mostly upward, and there
would be no chance of the arcs actually coming any
where near the In-Laws as they came down the little
shoveled path that he had prepared.
He carefully positioned a couple of dozen old
polyethylene buckets to hold the transmission
line, which was a couple of lengths of 1/2 inch
copper tubing that he had brazed together. He
giggled to himself as he fastened the transmission
line in place and attached it to the base of the
"extra" coil. Then he attached the other end of the
transmission line to the anti-corona ring of his
The secondary coil consisted of a single layer of
high voltage wire wrapped in a solonoid fashion
around a fair-sized plastic garbage can. This in turn
was nestled inside a piece of slightly damp cardboard
sonotube that was several inches larger in diameter
than the garbage can. The primary was several turns of
heavy battery cable that Bill had "borrowed" from work.
The high voltage capacitors were homebrew poly caps
in sections of PVC pipe and under mineral oil
(actually an off-brand of cattle laxative that he
had seen mentioned by Gary Weaver on the Tesla List.)
Not being able to find any decent clear poly, Bill
had managed to scrape up a mixture of "construction"
grade poly (that had lots of interesting things
imbedded in it), and some smooth and shiny BLACK
poly that he thought might work well, despite his
fleeting concern that it might contain large
quantities of carbon in the form of lampblack. What
the heck, what did he have to lose by trying???
Dozens of these capacitors were wired in series -
parallel to achieve the required voltage and
capacitance rating. Just a few days before, he had
discovered a mistake in his calculations and had
realized that he still needed more capacitance.
Not wanting to spend any more money and time on poly
caps, he decided to revert to making Beer Bottle
Caps. He had tried making Soda Bottle Caps once, but
they were not nearly so much fun to make as Beer
Bill had invited a couple dozen of his closest friends
over for a Bring Your Own Booze - Beer Bash. His wife
finally busted up the party at 4 AM Sunday morning.
Bill emptied out whatever beer still remained
in the bottles (I leave it to your own imagination
to figure out just how he did this). After many many
trips to the bathroom he finally had all the
empty beer bottles he needed. There were a fair
number of aluminum cans as well. These he put
in the plastic garbage bag in the kitchen.
While his wife wasn't looking he stole all the
aluminum foil and corn oil and salt that he could
find and proceeded to build a couple of tub-fulls
of beer bottle caps, which he then wired into the
existing capacitor grid using hundreds of little
Radio Shack clip leads.
The spark gap was an old circular saw blade that
was missing a couple of teeth. Why bother to pay
big bucks to that Wingate guy for a precision
built and properly balanced tungsten gapped rotary
spark gap with G-10 fiberglass wheel when you
could make your own for next to nothing?
Bill's own idea of a rotary spark gap was powered
by an ancient single phase AC motor that Bill had
scrounged from the local dump for a few bucks. The
motor and circular saw blade were connected
via a belt and pulley arrangement
since the shaft of the AC motor was somewhat bent,
and could not reliably direct-drive the saw blade.
As it was, when the spark gap motor was powered on,
the wooden base to which the entire Spark Gap
assembly was bolted would shake all over the place
and make an awful racket. Bill had jerry-rigged a
device that allowed him to vary the phasing on the
spark gap by rotating the motor by pulling on a
four foot long two-by-four. Bill had wanted to use
a ten-foot-pole, but I told him that nobody would
want to come near it with a ten-foot pole. That
seems to have convinced him.
Looking through the archives, Bill
had found a posting by John Freau on how to convert
small AC motors into fully synchronous motors.
Oblivious to the fact that the conversion pertained
only to SMALL AC motors, Bill modified his motor
anyhow, and found that after filing away large
chunks of his rotor that the modification only made
his motor lopsided. Now it REALLY jumped around when
he turned on the power. So he held the rotary spark
gap assembly wooden base plate as still as he could
by temporarily holding it down with a couple of old
lawn mower engines that he had hanging around.
He made a mental note to drop John a nasty note
telling him how useless his modification had been.
Back a few feet from the Spark Gap was the One Eared
Pole Pig. Thick high voltage cables snaked across
the floor from the Pig to the Spark Gap and the rest
of the Tesla Coil. Not wanting to cut the cables,
(which he had borrowed from work without asking)
Bill had left each cable its original length of
The Pig was fed a diet of 220 VAC from a 100 amp
Service Line. Now, the Pole Piggie was only
rated at 10KVA, but Bill had read somewhere on
the List that you could actually push a Pig to
two or three times its rated power capacity if
you kept the run short, (so that you didn't boil
off all the oil). Bill planned to test this theory
Now, Bill SHOULD have had a number of things that
he didn't. Such as common sense and an ON/OFF switch.
Being something of a cheapskate, he had decided not
to bother with installing a silly little thing like
an ON/OFF switch, because the guy at the dump wanted
more than two bucks for the ones he had in the big
box marked "Electrical Stuff". He knew that he
needed something to limit the current to the Pole
Pig, so he decided to wire a couple of toaster
ovens and a string of Christmas tree bulbs in
*parallel* with the primary of the Pole Pig. He
could have SWORN that he had read a post somewhere
(maybe on the Tesla-2 List) about putting some sort
of a load in series or parallel or something with
the transformer primary.
Bill knew that a variac was really a "must", but
he didn't have one. But he had read a post that
seemed to imply that you could modify a three phase
AC motor to act as some kind of a variable
transformer. Sneaking into the dump under cover of
darkness, he liberated a 400 pound three phase
AC motor that had once seen service in an office
building as the elevator motor. A few whacks with
an axe in just the right places and he had
de-commisioned one set of windings. He knew he
only needed two. But which two? He hoped it was the
two that still remained. He welded two metal stubs
to the casing and then welded a three foot length
of one inch diameter solid steel rod to the rotor
shaft. Now the motor shaft could only turn 90
It was still a minute or two before the In-Laws were
scheduled to arrive. One last check and Bill was
ready for an operational test. He turned on the
spark gap motor. Whump! Whump! Whump!
Whump! Whump WhumpWHUMPwhumpawhumpawumpawupa...
Yes, the spark gap assembly was a bit, uh,
Vibrational, but seemed to be holding together OK.
Bill lined the plug up with the socket (remember,
he had no ON/OFF switch), and rammed the plug into
the socket. BZZZZSHHHT! The spark gap lit up with
bright actinic light and would have fried Bill's
eyeballs in no time at all if not for the fact that
Bill (always safety conscious) had quickly put on
a pair of welding goggles. Now he could look at
the spark gap arc with impunity. Which he did.
Unfortunately, the goggles were so dark that that
is ALL that Bill could see.
Carefully shielding his eyes with his
left hand, he used his right hand to gingerly
lift the goggles and look at the Christmas tree
on the front lawn.
Outside, the Christmas tree came to life with a
pale glow of pink and blue corona that fuzzed out
for about two feet. But no arcs. No streamers.
What a bummer! He stuffed another wad of cotton
in each ear so that he could think again,
and taking a deep breath of the ozone-soaked air,
he groped his way over towards the modified
three phase motor. Grabbing a hold of the metal
rod, he strained to change the angle of the rotor.
Suddenly a forest of fierce white arcs as thick as
his arm broke out between the primary and the
He released the control rod. TWANG!!!! The rod
slammed itself into the short stub that acted as a
stop. Bill yanked the plug out of the socket.
The only sound was the whappawhappawhapa of the
rotary gap assembly, and the insistent
buzzing that was only in Bill's ears. DARN! The
secondary was arcing to the primary. Maybe if
he added a capacitive load to the secondary he
could get this sucker to stop arcing. He looked
around for something... anything... to use
as a capacitive load. His eyes came to rest on
the leering sharp-toothed smile of his butane
tank work of art, the Halloween Tank-O-Lantern.
To amuse the neighbors and anyone else foolish
enough to approach his house at Halloween, he
had fashioned a gruesome Tank-O-Lantern by using
a cutting torch to fashion leering eyes and
drooling teeth from the once-smooth surface of
the butane tank. The various burn marks from
the cutting torch operations made the tank look
even more sinister when the light played on
it just right.
Grabbing the Tank-O-Lantern, he managed to get
it to sit on top of the existing anti-corona
ring. It wobbled a bit, but what the heck.
For the second time that evening, Bill rammed the
plug into the socket. Again the spark gap burst into
life. The horrendous roar of the spark gap beat
against his ears as he grabbed the control rod and
pulled. A fierce blue corona outlined the eyes and
teeth of the leering Tank-O-Lantern, and as he
gleefully peeked out from under the welding
goggles, Bill could plainly see that beautiful two
to three foot arcs were issuing forth from the
branches of the aluminum Christmas tree. Not
bad. The system was obviously a little out of tune,
and he didn't have much more time before the
In-Laws would arrive, so he would just have to run
it the way it was. But he wanted the tree to look
a bit more Christmas-sy so he made a quick trip
to the attic and got some really awful Christmas
ornaments, (the kind his In-Laws liked), to
decorate the tree.
Unknown to Bill, while he was out decorating
the tree, his wife came out to the garage with a
bag full of garbage that she didn't want in her
kitchen for her parents to see. Looking
around in the garage she spied what she knew was
a plastic garbage can sitting inside what
looked like a cardboard container of some kind.
Seeing no other garbage container around,
she decided to dump the load of trash into the
plastic garbage can. So she did. And with
Bill was totally unaware that the coupling and
inductance of his coil had been changed slightly
by the addition of various beer cans and tuna
fish containers that had been dumped into the
core of his beloved experimental Magnifier Coil.
The addition of the glass Christmas tree ornaments
had little effect on the capacitance of the
Christmas Tree Topload, but Bill's last-minute
addition of a large copper toilet ball to the very
*top* of the tree had changed the isotropic
capacitance of the total topload just enough that
the "extra" coil and topload were in perfect tune.
When Bill saw his In-Laws exit their car and begin
their trip down the shoveled walkway that led
within a few feet of the Christmas Coil, he
stationed himself next to the power outlet and
waited until they were at just the right spot.
He jammed the plug into the socket and ran over
to the control rod. Little beads of sweat broke
out on his forehead as he pulled back on the
control rod. Meanwhile, inside the garbage can
secondary, RF induction heating was taking place
on the cat food tin cans. The heat caused the
garbage to shift suddenly, and in that instant
a wonderful serendipity took place. For a few
fleeting cycles, PERFECT resonance was achieved!
Megawatts of energy happily surged back and forth
in the slipshod tank circuit of the amazing
Christmas Coil. Phase angles slipped past one
another invisibly and fell in-synch. Due to a
couple of missing teeth on the makeshift rotary
spark gap's circular saw blade the caps ceased
to fire for a moment, and the capacitor bank
experienced an Anomalous Resonant Rise. An
instant later the excessive voltage caused a
particularly massive dump of energy into the
primary circuit at precisely the right phase
angle, and the resulting surge in energy passed
from the base of the wildly glowing Tank-O-
Lantern down the copper tubing transmission
line, which looked as though it were ringed
with fire. The transmission line was just
exactly the right length to allow the electrical
wave travelling down it to slam into the base
of the "extra" coil precisely at a zero voltage,
MAX current node. The "extra" coil and the
Christmas Tree Topload with round copper toilet
ball were exactly matched to the impedance
required, and the massive driving force of
Megawatts of resonant energy caused the
"extra" coil to react like a spring that had
been hit hard with a hammer. The resulting
jump in energy caused the voltage at the
Christmas Tree to exceed the breakdown voltage
of the winter air. With a mad, screeching
KaBOOOM the air broke down and a single
solitary streamer launched itself into the
cold dark night. Up, UP, *UP* it climbed,
and then, seeking the path of least
resistance, it curved over. Escaping the
intense electrostatic forces that existed at the
surface of the aluminum tree, the mighty bolt
of lightning swerved around and headed for the
nearest conductive object it could find.
The In-Laws would have been toasted alive were
it not for the one object that caught the Arc's
attention. Beyond the In-Laws, a good twenty
feet from where the Lightning Bolt had launched
itself from the infamous Copper Toilet Ball was
an old fashioned lamp post. It put out a dim
but cheery quantity of light that seemed
to beckon to the Wayward Lightning Bolt. Like a
giant white arm, the lightning bolt swerved around
and slammed into the cheery lamp post.
PHHHHHHHT! KABLAMMMMM! Like a gigantic flash lamp
the lightning bolt lit up the night with an
instant of blinding whiteness and a deafening
BLAM that reverberated in the In-Law's ears long
after their knees had stopped shaking.
A flash of light. A moment of raw, awesome beauty,
and then DARKNESS as all the electricity for blocks
around ceased to flow.
It is a Christmas that Bill will always remember.
It is a Christmas that his wife and In-Laws will
never let him forget.
This is just a story. Any resemblance to any persons
living or dead named Bill is merely coincidental.
As the author of this tale I want to say that the
story is not meant to be a plan for how to build
your own Arcstarter -er- I mean, Magnifier Coil.
The theory contained herein is only partially
believeable, and is not meant to be a factual
accounting of what actually happens in a Tesla
I hope you enjoy this little romp in the spirit
in which it was written.
I wrote it especially for my good friend (at least
he WAS my good friend), Bill the Arcstarter Pollack.
But, as the disclaimer said, it is not actually
ABOUT him. Even though he does hate cats and
build Tank-O-Lanterns, and dabbles in Tesla Coils.
This story is just about a Bill who happens to
be an awful lot LIKE Bill Pollack. The real Bill
would *never* borrow anything from work without
asking. He is beyond reproach. He is my friend.
Fr. Tom McGahee
Tesla List and Tesla-2 List Member