First light and problems
From: Esondrmn-at-aol-dot-com [SMTP:Esondrmn-at-aol-dot-com]
Sent: Wednesday, June 24, 1998 10:27 AM
Subject: Re: First light and problems
In a message dated 98-06-23 03:21:30 EDT, you write:
<< From: Marco Denicolai [SMTP:marco-at-vistacom.fi]
Sent: Monday, June 22, 1998 12:43 AM
Subject: First light and problems
Last weekend I got my ground and my first TC ready: I had no variac and I
it up at full power. I had before measure primary and secondary to resonate
both at 240 KHz so the primary tap should have been about in the correct
IT WORKED! I had about 1 meter long sparks running from the toroid into free
air, almost perfectly horizontal. After the first minute I run into
1. I got 1-2 sparks from the strike rail hitting the middle of the secondary.
I suppose my strike rail was too much near the secondary (the sparks made a
10" travel from strike rail to the secondary body).
2. Then I got some sparks from the inner primary turns to the secondary base
and primary to secondary about 3" height from its base. Because it was day
and I was (safely) far from the coil, I couldn't notice any corona or aurea
effects near the primary base, but I suppose the problem was the well known
3. One diode from my MOT doubler blow up twice (always the same one).
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.
Primary turns and secondary first turns almost on the same horizontal plane.
Tank supply made of two MOTs and two voltage doublers, output 8 KVAC,
almost 0.5A (I believe). A third MOT primary (with shorted secondary)
was 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 3 of 0.275" gaps
connected in parallel.
About the following solutions I would like very much some comments:
Problem 1: I plan to rework my strike rail as an open ring about 3" high
from the secondary base, about 8" horizontal clearance from the secondary
Problem 2: rework the primary, increase the clearance between inner turn and
secondary to 1", make it a 15 degree upside-down saucer to distribute better
it magnetic field and decrease coupling.
Problem 3: the two MOT employed were a 900W and a huge 1500W. The diode of
the doubler of the last one keeps on blowing. I replaced the 1500W with
900W and I hope this will stress less the diode.
Your opinion is really welcome...
I would definitely reposition the strike rail so it is slightly outside of the
last turn on the primary and up about 2.0" above the primary (2.0" clearance).
I would open up the primary and allow about 1.0" clearance between the
secondary and the inner turn of the primary. I would leave it as a flat
pancake. Space the secondary up about 1.0 or 2.0". Now put something in
series with the line power to the MOTs to reduce the current, preferably an
inductor like a variac or welder or even resistive ballast. You need to do
some tuning at lower power to make sure things are tuned properly and to check
the coupling (in the dark) before again applying full power -- or of course
get a variac to control the beast.