What next for longer sparks?

From:  Adam Parker [SMTP:park_e_r-at-hiwaay-dot-net]
Sent:  Thursday, July 02, 1998 1:30 PM
To:  Tesla List
Subject:  Re: What next for longer sparks?

<<<-----Original Message-----
From: Marco Denicolai <marco-at-vistacom.fi>
To: tesla-at-pupman-dot-com <tesla-at-pupman-dot-com>
Date: Wednesday, July 01, 1998 12:29 AM
Subject: What next for longer sparks?

After 3 hours of running my TC I got a strike from toroid to the primary
killed one of my doubler diodes. I had no strike rail that time. I replaced
now the single diodes with two diode pairs (two diode in series). In
parallel with each of the 9000KV 350mA diodes a 33Mohm 3.5KV resistor
and a series of two 1.5nF 3KV capacitors. Guys, that was the best I could
get from the local store! I also grounded back my strike rail.
In a few days I'll be testing this new setup.

Anyway, after initial excitement, I was able to precisely measure strike
length to a grounded rod and that was 20" (not 1 meter as I wrote same time
ago). That means that the primary-secondary rises my tank HV roughly by a
factor of 60 (from 6.5 KV to 400 KV).

The voltage drop in my tank (from 8KV to 6.5KV) is due to the third MOT
works as a reactor in series with the MOT primary windings. Without that I
always blow my 10A fuse.

My questions are:

- is 20" the best I can get for my tank and my secondary size?
- what should I do to increase the streamer length?

I ask this because I feel (primary capacitor size, MOT max current, etc.) I
have got plenty of power to get longer strikes. What is the best way to go:

- bigger toroid?
- bigger secondary?
- more coupling (I didn't go lower than 1.5", I didn't reach overcoupling
- different spark gap?

My coil data:

Secondary 4.33" diameter, 19.7" wind with AWG 26 enamel wire, 7 layers of
epoxy paint. Toroid 3.15" diameter tube, 11.4" outer diameter, 12.7 pF.
Mounted 1.6" over the secondary top. The pair resonates at 240 KHz.

Primary 7 turns of 3/16" copper tube, inner diameter 5.3", turn spacing
0.3". Flat pancake. Clearance from inner turn to secondary 0.5".
Secondary capacitor 0.05uF 50KV. Set to resonate also at 240 KHz.
Secondary first turns 1.5" higher than primary first turn.

Tank supply made of two MOTs and two voltage doublers, output 6.5 KVAC,
almost 0.5A (I believe). A third MOT primary (with shorted secondary)
is in series with the 2 MOT primaries on the 220V side to work as a shunt.

Spark gap is a RQ static gap with blower and two series of 2 of 0.275" gaps
connected in parallel.>>>

This is probably the blind leading the blind, but here i go.


I don't think many serious coilers would ever reccommend building a
secondary less than 6 or 8" in diameter. Also try using larger wire (22 AWG
or bigger). Don't buy Schedule forty PVC unless you have to. Try to find
the kind with the thinnest wall possible. Coat your form with heavy coats
of epoxy or polyurethane BEFORE and AFTER winding. This helps to negotiate
PVC's poor RF qualities. You can try more turns on the primary (I like to
aim for about fifteen!) There's probably another you could keep your neons
from blowing the fuse without compromising power, but its still too early
in the morning for me...