Re: Herrick's Transformerless Tesla Coil

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

Original poster: "K. C. Herrick" <kchdlh-at-juno-dot-com> 

If anyone (other than Dave Leddon) is interested...

My design of the
http://hot-streamer-dot-com/temp/tspk17s1.pdf>http://hot-streamer-dot-com/temp/ts
pk17s1.pdf concept proceeds nicely:

1.  I've ordered a motor for the RSG/commutator (the
http://www.surpluscenter-dot-com/item.asp?UID=2004021916545907&item=10-1526&c
atname=electric one), which seems just right.  It's an industrial
sewing-machine motor, 0-90Vdc, 0-7000 rpm, face-mounted, 1/2" shaft.

2.  I'll use, for the gap's rotating element, a single 7" x 5/32"
tungsten rod (not the balls I show on the dwg), McMaster-Carr #8000A72.
My thanks to a List-poster or two for steering me to such rods.  For the
stationary gap elements, I'll use a pair of very nice 1/2"-dia. tungsten
balls that I find I've had squirreled away (for decades).  Complete with
3/16" shaft-holes & set screws!

3.  For the rotating "brushes", I'll attempt to use two paired wiper
contacts from P&B KU-4928 relays.  I have them in the junk box & they
look sturdy enough, at least for intermittent use.  I'll dismount them
from their armatures & remount them on the rotating assembly.

4.  I plan to mount the motor unconventionally: concentric with the
secondary coil.  The motor is face-mounted & not very deep so it would
not raise the primary assembly up very much from whatever "earth" the
whole thing is to sit close to.  With the commutator/gap at the center,
all conductors to it are kept to minimum lengths; most importantly, those
leading to the gap.

5.  I plan to mount the rotating components on a rectangular
linen-phenolic substrate fastened to the face of a 1/2" steel
shaft-collar.  The tungsten rod is to stick out at each end and the
relay-wipers are to be suitably mounted, tangentially, so as to press
against an adjacent phenolic disk assembly that will hold the stator
contacts.  For those, I'll use copper sheet-stock.  I have yet to figure
out how to mount those contacts; perhaps a good epoxy.  Earth-grounding
of the gap rod will be through the shaft of the motor & via an axial
brush at the bottom end of that shaft; very convenient--and with the same
thing at the top end of the shaft, I could ground the low end of the
secondary at the same time.

6.  Kindly do not snicker...but I intend to mount the RSG/commutator
assembly, the "coil" and the capacitors on a large plastic commercial
salad-bowl.  I have a 24"-diameter one that's a little too big, so will
find a somewhat smaller one.  They're very sturdy, will accomodate the
motor on the flat bottom, and will offer an ideal substrate for mounting
the "coil" & capacitors around the periphery.

7.  For the "coil", I'll use McMaster-Carr #5174K8 3/4" soft Cu tubing.
I'd like the 7/8" size but the price goes 'way up.  It will not so much
be a coil since six 120-degree arcs of it, in two rings of 3, will
constitute primarily the mounting means for the capacitors.  Most, or at
least a good part, of the 1-turn inductance will reside within the
capacitors.  I'll separate one of the segments into 2 pieces for
connection to the gap electrodes.

8.  For the capacitors, I'll use the CDE 942C8W2K 2 uF/850 V ones.  I
haven't summoned the courage to get a quote yet on them; I suspect
they're pretty dear.

Ken Herrick