5-gallon mini coil! (LONG POST)

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

Original poster: "by way of Terry Fritz <twftesla-at-uswest-dot-net>" <jduva-at-baytechnologies-dot-net>

Greetings, TCML!
	Well, I've been on the downsizing kick for a few months now and
finally decided to do something about it.  No more 15/60 4" coils in the
apartment for me, thanks.  I scrounged up a very used-looking 4/60 NST and
decided to see if I could do anything with it.  I'm nearing the end of my
project, but I have a few design questions that I'd like to throw out to the
list.  First......a little background info!

	At first, I had some concern about the firing voltage being a bit on
the low side, but I knew that I could start an arc between lead coming from
the HV terminals of this NST at a distance of about 1/8"-1/4", depending, so
it wasn't completely impossible.  A few minutes digging for the static gap
from my first coil and adjusting a few copper tubes, and all was looking
good.  I wired up a 30nF maxwell pulse cap for further testing, threw in a
very tight safety gap, and tried it out a bit more.  All was loking good,
but I could really only get reliable performance using 3 gaps in the static
setup.
	Next came the secondary wound on 1.5" PVC pipe with 8" of 33-guage
magnet wire, and a John Freau (tm) 1.75"x6" spun aluminum toroid was slapped
on the top for a topload.  No baffles were installed.  The primary was wound
with 12-gauge solid copper  wire on the bottom of a white 5-gallon plastic
bucket with 10 turns.  The inner turn diameter was 3".
	I got no corona from this setup, and only was able to pull a maximum
of 3" from the toroid at 10 turns on the primary.  Before I could get around
to winding a new flat primary, I burned out the secondary with experiments
with a vertical helix.  I should add that the static gap also gave up.  As
Mr. Sundog had pointed out to me (I hadn't thought about this), the high
current and low voltage combination through the static gap could cause
problems with quenching and heating.  It did.  I burned notches into copper
pipes and the arcs between them changed from bright whitish-blue that
traveled up and down the pipes, to yellow-white power-arcs that stayed put
right where the notches had been burned into the copper pipes.

	Currently, the secondary has been replaced with a 2" PVC form, wound
12" with 33-gauge wire for approximately 1550 turns.  Same toroid, same flat
primary wound with the 12-gauge solid conductor stuff, but the spark ap got
replaced by the bulky sync rotary gap that I use for larger coils.  With the
Maxwell cap, I was able to get 4-5 simultaneous streamers up to 6" in length
with no breakout point, and with a little help, I could get a single 10"
streamer.  A small 40W appliance bulb on top of the toroid also allowed good
performance, and allowed the streamer to shoot straight up.  I got to see
what all the fuss was about with the telsa tornados, too!  Very, very cool.
The light bulb seemed to helped my tuning a hair and gave a noticable
increase in spark length, but I'd say it was only an inch on average and
maybe 2" max length into the air. (I used insulated wire on the primary
since it was all I had at the time and my tap points are limited to the
spots were I've stripped the insulation).
	The thought struck me a while ago to try and fit everything needed
to run the coil inside of the 5-gallon bucket that's got the primary wound
on the bottom.  The small 4/60 NST, Terry's protection filter, and the tank
cap could all fit easily enough, leaving plenty of room for a sleeve to tuck
the secondary into when not in use (and right-side up), but there was not
way that I could fit the big sync rotary in there.  I started toying around
with a very small 3600rpm laser printer sync motor, but had some immediate
trouble with the 3/16" shaft on the motor.  Two nights ago, I finally
decided to press my luck and took out the dye set.  I was able to thread the
end of the motor, but only down to where a certain shaft collar had managed
to get itself stuck (which I guess isn't too bad, since it can't be moved
around).  The disk is 5.5" in diameer, cut from 1/8" poly-carbonate sheet
with a hot knife repeatedly heated over the gas stove burner, then trimmed,
filed down, a smaller circle scribed around it with a compass, then drilled
to fit over the motor shaft and to accept #6 brass machine bolts.  I opted
for the next size up and tapped out threads in the disk for #8 bolts
instead.  The electrodes were made from 2" long #8 brass bolts with the
heads cut off.  Stationary electrodes were mounted on a 4"x6" project box
from Radio Shack, and the motor and disk were mounted on the metal cover to
the box.  The inside of the project box now houses an MMC bank with 4
strings of 6 of Terry's Panasonic caps (56nF 1600V DC), with every strong
selectable from the outside of the box. .5" holes are drilled around the box
for air flow as well.

	Here are my questions....    (I will post pictures tonight or
tomorrow night with Terry)
	Apparently, I don't have much precision with my hand-held drill on a
carpeted floor for doing	work on rotary disks, because my electrodes
are off by almost 1/8" from the center of the disk, causing a slight bit of
vibration at 3600 rpms, and causing major problems with adjusting the
stationary electrode on the side to be close enough to let 5kV arc from it.
If the motor is off, and one of the flying electrodes is placed across the
stationary electrodes, the gap MOSTLY fires reliably.  But if the motor is
up to speed, and phased correctly, the gap fires intermittently at best.  
	I'm thinking about starting easy with this and going with a static
gap, but I don't havea great deal of confidence in bolting a bunch of copper
tubing sections perfectly parallel to each other and only as far apart as a
business card.  The whole gap also has to mount inside of a plastic bucket,
or be built in the bucket wall itself (which seems like trouble to me).
	Also, before this 4x6 MMC bank, I was using a 2x4 bank with the same
Panasonic caps, and twice, the second cap in from the primary coil side on a
string 4 would short out internally, blow out, and catch on fire.  I'm
guessing my safety gap wasn't set very well for the things to blow in the
first place, but why that position both times?  Here's a short ASCII
diagram.  The capitalized caps are the ones that blew out (first the bottom
one, then replaced, run again, then the top one blew out).

		MMC cap bank

primary coil -> 	cap+CAP+cap+cap ->	spark gap
		cap+CAP+cap+cap

Thanks for reading this far!  :)
Thanks for help, in advance, also!
To keep things small, I only ask that the parts of the original message that
are bing replied to get included in any reply messages.  I can't remember
for sure, but I think something was said about growing thread messages
filling inboxes.

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-Joe