RE: Newbie with questions...

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

Original poster: "Lau, Gary" <gary.lau-at-hp-dot-com> 

My comments:

1) As you noted, the 0.75" diameter secondary is on the narrow side.
2) If and when you upgrade to a wider secondary, you may find that the 
coupling with your helical primary is too high, and a flat spiral primary 
may be a better idea.
3) Your tank cap is too small, you'll get better performance with something 
in the .01-.02uF range.  Five 0.1uF/2kV geek group caps in series would 
work nicely.
4) A single static gap is good, but using two screw tips is not.  Since the 
arcing occurs at a single point, it gets hot, which generates a lot of 
metal ions, which lowers the gap breakdown voltage and degrades 
quenching.  Instead, use two parallel copper pipes, any diameter over 1/2", 
a couple inches long.  This spreads the arcing area out so no one spot gets 
hot.  Blowing air across the gap has ALWAYS, in my experience, helped 
performance.
5) A 0.125" gap may be pushing it, a half inch is suicide!  Always set the 
gap by disconnecting the cap and adjust the gap until it just fires when 
wired across the NST.

Your experiment with removing the top load doesn't sound right.  You didn't 
say what your top load was, but the choice of top load will profoundly 
affect the secondary frequency, and since that has to match the primary 
frequency, it doesn't make sense that you can change it and not the primary 
with no effect.  The size and shape of the top load is extremely 
critical.  Up to a point, increasing the top load size and retuning the 
primary to compensate will improve performance.  Beyond that (generally 
when the top load "looks way too large"), you'll not be able to get the top 
load to break out.

Hope this helps, Gary Lau
MA, USA

=========================================================

Original poster: The MCP <ejkeever-at-comcast-dot-net>

Hello, everyone. I just signed up and have some questions to ask about some
aspects of coiling.

I've built a small (tabletop-size) tesla coil for fun, and I am observing some
very odd behavior from it. But first, I should provide some basic info.

The secondary is a .75" PVC pipe (I got excited and built it before doing
enough research), with about 10.5 inches of 32 gauge magnet wire on it, about
1000 turns. The helical primary is 5 inches in diameter, ~3.5 inches tall,
with 5 turns.

The main tank circuit has a smallish 5000/20 NST and currently a single
40KV/2nF cap from TDK that I picked up for $30.

The spark gap is a simple static gap, currently separated by about .125
inches, using the tips of a pair of screws. When these wear out, I can just
replace them with fresh ones. The gap can be set for up to 1/2 or so inch
separation.

Currently, the whole thing is in a highly experimental state. By that I mean
that very little is set in stone; Almost all the major connections are either
twisted together or clipped. So you've got a lot of latitude to change
things.

Anyway, on to my questions. First of all, I'm wondering if I've got any of the
components grossly off-key. Comment away.

Second, I've found something odd( to me at least). One day, just for the heck
of it, I took off the topload and stretched the wire straight out. Nothing
much happened. But when I took the 6 inches or so of wire and wound them into
a small spiral (about 7 turns, 3/8 inch diameter, 1 inch long), the coil
worked almost as well as with the big copper topload so I abandoned it. Can
someone tell me why?

Thanks for taking the time to slog through all this and answer my probably
silly questions!