Original poster: Daniel Hess <dhess1@xxxxxxxxxx>
Terry;
Re; your comment,
"But it suggests that "very low" coupling may be a good thing.... Like a
coupling of 0.03!!!"
I noticed something just this past weekend which seems to support the idea
that lower coupling might be better. About a year ago I built a SRSG for
my coil and designed the motor to fit in to a cradle so that it could be
rotated to provide a means to advance or retard the firing angle. I used a
stepper motor assembly to rotate the motor in its cradle but never got
around to building the stepper motor controller. So in the meantime I just
adjusted the motor manually in a trial-and-error fashion until I got (what
I believed was) the best output. This past weekend I finally completed the
controller and for the first time was able to adjust the SRSG on the fly
and some things became readily apparent.
For one thing it turns out that my original static setting was too
advanced and as I began to retard the setting and it came in to tune, the
sparks got longer, brighter, it got louder (goodness) but I also began to
develop racing sparks along the secondary and for the first time, the cap
safety gap started to fire. I tried to gently push it a few times and the
racing sparks and cap S-G firing were consistent and proportional to the
degree that I retarded the SRSG. Even at lower power settings on the
variac where I wasn't getting the racing sparks the cap safety gap went
ballistic! Could the firing angle of the RSG have any bearing on resonance
between C1 and the NST secondary? (my C1 is an mmc @ .049 uf and the NST
is a 15,000 x .120) Or put another way; perhaps the angle of the RSG has
no bearing on the resonance between C1 and the NST but running it so far
advanced attenuated any naturally occurring resonance?
Years ago, I set the coupling of this coil to one of the magic K values of
.18 using the suicide cord method. (applying 120 VAC to the secondary and
measuring the induced voltage in the primary, then computing the value of
K and adjusting the coil height to the desired value. .18 was as tight as
I could go since any setting higher introduced severe racing sparks in
this coil. I was disappointed that I could not achieve a higher coupling
but wrote it off to the physical dimensions/parameters of the secondary,
that had provided a ceiling which prevented me from going to a tighter
coupling. But it never occurred to me that perhaps a LOWER K value might
allow me to retard the SRSG to a close-to-max position sans the racing sparks!
I'll whup out my suicide cord later this week and readjust to the next
lower magic K value (or maybe several steps down) and post the results
soon. BTW, I attached a scale and pointer to the body of the gap motor so
I can reference how far I've rotated it and in which direction. The scale
is really handy because, if I ever get totally out of tune the scale
allows me to quickly return to my starting point.
Daniel Hess