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Hi Doug, I would urge you to consider using a static gap until you are an experienced coil builder. There are many pitfalls to successfully designing a coil using a rotary gap that are not evident to beginners. Advice is often given recommending that NST powered coils use only a sync RSG. I don't think there is anything inherently wrong with using an async RSG with an NST. The real danger is using a variable speed motor and running at too low an RPM that the cap doesn't discharge every half cycle. The voltage builds on successive cycles until either the cap or NST insulation breaks down from over-voltage. A properly set safety gap would protect against that, but the discipline to correctly set that is uncommon. 13,000 RPM? The speed for a sync RSG is only 1800 or 3600 RPM, so you'd have to throttle that way down, and risk going too slow. Regards, Gary Lau MA, USA On Mon, Sep 17, 2018 at 7:52 PM doug <doug11642@xxxxxxxxxxx> wrote: > I am building a rather small TC for [Ross Reynolds] a physics prof. at > GVSU here in Allendale Mi. I have a sewing machine motor that turns at 13K > – plus, under no load and would like some design ideas for using it to > build a rotary spark gap for the little {demo} coil please. > To give you some idea on the coil/ NST = 7.5/30, MMC = 18K X 5.2 nf, top > load = 1.5” X 6” toroid. > Any help you give me will help to inspire some students {maybe}! > This coil, by the way, is a gift to my friend Ross! > Doug J. > _______________________________________________ > Tesla mailing list > Tesla@xxxxxxxxxxxxxxxxxx > https://www.pupman.com/mailman/listinfo/tesla > _______________________________________________ Tesla mailing list Tesla@xxxxxxxxxxxxxxxxxx https://www.pupman.com/mailman/listinfo/tesla