Sync RSG instability

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

Original poster: "Lau, Gary by way of Terry Fritz <twftesla-at-qwest-dot-net>" <Gary.Lau-at-compaq-dot-com>

I'm slowly working on getting my sync RSG ready.  I've hooked it up to
my coil with a 15/60 NST, a .02uF/45kV Maxwell cap, and in place of the
primary (and secondary) I've substituted a series-pair of 120V/500W
halogen light bulbs to dump the cap's charge into until I'm sure I've
got everything right.

I'm scoping the voltage coming off of the protection network with a
fiber optic probe set and digital storage scope.  My RSG is built in
such a way that I'm able to rotate the motor housing in it's cradle
while it's running to vary the phase.  The motor is a 3600 RPM teletype
motor, and the rotor has two electrodes for 120BPS.

What I see is largely what I expected.  I can vary the motor phase and
the bulb brightness varies in the way I would expect.  The peak
brightness comes when the gap fires at or perhaps just after the peak
charging voltage is reached.  Since my cap is LTR by a factor of about
2X, in theory the greatest power should be delivered when the gap fires
somewhat AFTER the peak charging voltage of about 25KV.  This is not at
all intuitive but has been demonstrated by both simulations and the
experience of others.

BUT, when I advance my RSG timing to fire any later than slightly after
the peak charging voltage, the gap stops firing, the charging voltage
waveform changes to a full 35KV (!!!!) sinusoid, and the phase of the
waveform shifts by 90 degrees, such that the zero-crossings are now
occurring at the gap presentations, which is why the gap doesn't fire.
If I retard the timing, it will again resume normal firings.

The two RSG Gaps are very close, not more than perhaps 40 mils total.  I
can't see how my dummy load could be causing or affecting this, though I
can't be certain. I would try the RSG with my normal primary and
secondary, but my house is not yet ready for live coiling.  Has anyone
else seen this behavior?

Gary Lau
MA, USA