Dayton?, been there, done that! I arrived late Thursday afternoon,
snuck in and did some early shopping. Scoured the flea market the
entire day Friday and got a nice sunburn. I wore my Tesla badge
prominently and also placed a sign in the window of my van, parked
where my previous post said I'd be. I received no messages left
under my windshield wipers, nor did I run across anyone from our
group at the fest. That was a real disappointment.
I found some Tesla-able components suitable for small coil work
including a 12KV-at-30MA neon (which works!) for $5, and a couple of large
capacity (~20A.) 120 volt variacs which I really need for the bench.
There was a company, Surplus Sales of Nebraska, which had both a
space outside as well as a booth inside the arena. They had a single
sample of a large metal can GE capacitor which they said some guys
were buying for Tesla coils. Value is 0.04 mfd -at- 40 KVDC. The unit
is very big for that value, approximately 12"x10"x10" with a single 6 inch
clear glass bushing on the top. The wire connecting through the
bushing is visible and looks like a #12, maybe a #10 AWG (marginal).
They must be selling these by the pound because they are about 35-40
lbs?, and the asking price is $120 (too much!). Because this looks
like an 'old technology' capacitor, and the unit itself is clearly ancient,
my guess is it is comprised of kraft paper and mineral,
maybe caster oil. If a plastic film also shares the dielectric space
(not required for DC filter or non-reversal DC pulse applications) it
will not likely be the good low loss type desired for Tesla coils,
and even if it was polypropylene, polyethylene, or teflon, the
paper in there would screw up the RF performance.
If anyone out there is really hard up for a capacitor and is a good
bargaineer who might be able to talk these guys down in price (for
$40, I would take a chance) their number is 402-346-4750. I think
they have a dozen or so at the store.
There was one guy who had a bunch of very high voltage plastic
Maxwell capacitors (late model). I remembered looking ito their
Tesla capabilities before and knew that they were designed for low
(1 Hz ) rep rates and no reversal. These are super compact, latest
technology pulse discharge caps that the big government labs use for
laser work and so on. You need the electron microscope version of an
inductance meter to measure their internal series inductance.
Many were large values at 30KV or so but he had a few 75 and 100KV
units at 0.04, 0.06, and 0.08 mfd. Knowing that the dielectric would
run hot in Tesla service I chose not to buy the entire lot but
gambled by picking up his only three of 0.04 mfd -at- 100KV units.
I reasoned that since my AC applied would only be about 10% of their
DC rating, and my AC reversal would only be around 30%, these units
might behave in Tesla service. I'm now back at the lab and have tried these out.
Running from a
7000 volt pole pig type transformer the single 0.04 mfd does indeed
get warm quickly, so coil duty cycle with one of these units would be
very low, but boy, they DO WORK WELL! I tested them at 180 KHz.
At 50 KHz they would heat less. At just $25 each I wish now that I had picked
up many more. Did anyone else out there 'discover' and more
importantly 'buy' any of these Maxwells?????????
1000 miles wearier, rwstephens