Re: I want 2-footers, and I want 'em now! (fwd)
---------- Forwarded message ----------
Date: Wed, 13 Oct 1999 09:48:58 EDT
Subject: Re: I want 2-footers, and I want 'em now!
Apologies for the long-winded text that follows, I figured the more detail I
gave, the better your advice will be.
I'm a newbie. I'm using a 15,000 V -at- 30 ma NST for my first TC and what I
have been reading here indicates with a good design I should get 2 foot
streamers. I can''t seem to break the 6" barrier.
Heres' what I started with:
The TC is loosely built around plans in the current Nuts&Volts, so I've
followed their schematic.
Primary: 8 turns of 14 awg copper on a 9" diameter circle, spaced 1/2" apart
Secondary: 800 turns of 28 awg on a 3.5" diameter by 14" PVC form. Coil is
Capacitor: flat plate type just like in the article, 4 pieces of 10x10
aluminum flashing with .030 polystyrene separators (I had it laying around, I
think it's polystyrene - white, flexible, opaque, and dirt cheep). The DOS
software I downloaded indicates this is .0054 uf.
RF coils: just like the article, 21 turns of 18 awg on 1.5" PVC pipe (which
is really closer to 2" dia), one coil in series with each secondary of the NST
Input xfmr: 15,000 volts at 30 ma NST
Regular spark gap with 1/4" cap nuts.
Toroid made from two 1 1/4" plumbing "J" traps, cut and soldered together -
"Ground" rod from one side of primary to a point about 5" above center of
I sent the above info to Nick off-line and he suggested doubling primary
turns and quadrupling # of plates in the cap. Here's what I did:
I doubled the primary turns by halving the spacing (16 turns at 1/4" spacing)
and finally experienced "tuning" at 11 turns. Now I have a feel for the
difference between resonance or not.
This gave me 5-6" streamers but still required a 3/8" gap, and I started
getting secondary-to-secondary strikes between points about an inch or two
apart on the coil. I also saw the capacitor arcing between the connection
points and the opposite plates (sneaking through the gap between the
separators), even though there's a good 1" overlap on the separators.
So, I took the cap apart and found I mis-measured the thickness, it's .047
not .030. I siliconed between the separators near the terminals and added 4
more plates. The DOS software I have indicates this should be 1.2nf per pair
of plates. I assume that means 8.4 nf for a 8-plate cap (1.2 x 7).
Now it tunes at 6.5 turns with a gap of 1/4" but I still can't get more than
6" streamers. The cap no longer arcs, but I still get some sec-to-sec
strikes even after spraying with high-dielectric conformal coating. Help! I
want 2-footers by Halloween. I can build caps and/or wind a new secondary or
primary between now and then but I'm stuck with the NST I have. I could
maybe build a more complex spark gap, but not enough time for a rotary or
I also have these questions:
1. The DOS software suggests 5.3 nf is perfect for my NST, but it seems like
you guys go by the "bigger is better" principal. What's up?
2. I see a lot of talk of refrigeration tubing for primaries. Why? We're
only talking about low currents, right? What's the advantage of refer tubing
over 14 awg wire?
3. I see discussion of primaries, secondaries, caps and spark gaps, but no
mention of RF coils like the Nuts&Volts article uses. Should they be used or
are they just insignificant enough to not warrent discussion?
4. The N&V article did not mention any particular grounding other than
connecting the bottom of the secondary to the NST ground (which is connected
to electrical ground). This is what I have. Good? Bad? Ugly?
I would love to see someone elses work, and a working TC, but it sounds like
you guys are scattered everywhere. I'm in Atlanta. Anybody close?