FW: 15/120 NST Coil Static Gap Performance Problems

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Original poster: "Ian McLean" <ianmm-at-optusnet-dot-com.au> 

Hi all,

I having a difficult time trying to understand this problem, so it's going
to take a bit to explain, so sorry all in advance for the long post :) :)

Tuned my 6" coil last Saturday afternoon with the help of Claude.  I don't
have a decent static gap, so Claude kindly brought along his sucker gap,
control box which has a current meter, and an extra variac to help tune the
SRSG and to control the suction to the suction gap - BTW: thanks for
Saturday Claude :-)

Firstly, we got some good streamers on Saturday :)  Especially with my SRSG
and the 62.5nF tank cap.  Some nice bright power arcs to the colourbond
roofing and overhead metal pipe.  Some out to 5 foot.  One power arc to
ground, through a vice mounted on my workbench.  The 5 footers at the end of
the day, when both Claude and I think we just about got it right, wanted to
go further.  A couple of streamers arced through a metal jerry can on a
shelf, through the half inch thick wooden shelf above it (directly through,
it was no barrier at all) and upwards to the furthest point on the corner of
the ceiling 5 foot away - so I am getting very close now to predicted
output.  It was definately limited by the roofing.  I am now getting
prepared for an early evening full power outdoor test.

I learnt a few things on the day.  Don't use GTO-15 for tank cable -
dramatic drop in output.  This was the first thing changed, for some thick
multi-strand copper cable, and the output instantly improved.  This was
unshielded - so I am going to get some even thicker copper multi-strand and
shield it myself.  I learnt not to let this unshielded copper touch the
varnished wood of the primary base (it caught on fire :-0).

And now the mystery.  My coil didn't respond too well to the sucker gap.
Streamers about 4 foot max.  But that's not the mystery.  No matter the
tuning, tweaking, adjusting of coil coupling, gap size,  cap size (LTR
static -at- 37.5nF or LTR rotary -at- 62.5nF, or sucker suction velocity, the
output did not improve beyond this, and the gap seemed to sputter, and
seemed to be at a low break rate (slower than SRSG at 100bps, you could
easily tell the difference between the two).  Now neither Claude nor I could
understand the reason for this, so if anyone can shed some light as to why
????  Is my 15/120 NST bank not getting the caps charged enough ?  Current
draw with sucker gap was 15A average, tuned, from 240VAC mains (Australian
supply).  With SRSG, tuned, that dropped to about 10A average.  This sucker
gap performs much better on it's owner's (Claude's) coil.  On his coil, it
roars like a chainsaw on heat, and the gap spark is much brighter.  On my
coil, it is loud, but not as loud, and the spark brightness is sputtery and
not quite as intense (although still very very bright).

My coil instantly performed well on the SRSG, once tuning and SRSG alignment
had been tweaked.  5 footers wanting to be longer.  Nice bright power arcs.
Clean 100bps break rate.  Very loud but even sounding.  Very smooth.  I like
the way the streamers seem to "snake out" of the toroid, and fork more, on
the SRSG.  Noticed this on Claudes coil as well.  Even breakout over the top
toroid, with some arcs and streamers moving around the toroid.

Wish I could have taken pictures.  My sister will be at my place on
Wednesday, with her digital camera, so I'll do an outdoor SRSG run in the
early evening and get her to take some pictures of it all for me :)  Hoping
for 6 footers.  Wish me luck :-)  I'll get some photo's up on a Web page
somewhere.

Any help with the sucker gap performance problems would be greatly
appreciated.  I want to build one.  I like the more random and thicker,
brushier output (albiet shorter) it gives as well.

Rgs
Ian