I need advice on sync spark gap

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Original poster: "Robert Hanford" <pomnept-at-comcast-dot-net> 

Hi everybody, I have a problem that I'm sure is a no- brainer for most 
experienced coilers.
My coil has been working fine with a vacuum gap, so I thought I would 
experiment with a SRSG. Worked well at low power, but could not find the 
"sweet spot" at full power, even with quite a bit of monkeying around. I 
pulled the safety gap out a "little" too much, then it worked real well for 
a few seconds, then my MOVs went kaput.I am using a Freau phase controller, 
.011 MMC cap, 15k/60ma NST, and of course a SRSG. And a 4.5 inch secondary.
Well, the damage was done, so it was time to quit. I haven't checked my NST 
yet.
I hope somebody might give me a few ideas about possible errors- what was 
frustrating is that it was working so well at lower power. Do I need a 
larger cap?
As always, any help is most appreciated.
Robert Hanford