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Re: Redesigning/tuning a coil
Original poster: "Dr. Resonance" <resonance-at-jvlnet-dot-com>
With your 8.75 inch OD secondary coil keep your primary a flat spiral. This
large dia. will produce overcoupling. Also, a flat test "scrap wire"
primary with 25-30 turns can be quickly set up with some slotted scrap
cardboard for a quick test of your entire tuning range. Keep your sparkgap
setting tight (under 0.100")and your variac below 30% until you find the
best pri resonant point.
With a NST your goal is to add capacitance until you can hit resonance at
10-15 pri turns. Then you can make your "final polish" primary with delrin
blocks 3/4 x 3/4 x 1 inch and nice 1/4 inch refrigeration copper tubing.
After everything is in resonant tune you can also experiment with elevating
the sec in 1/2 inch steps (checking to obtain best coeff. of coupling for
With an 8 inch dia sec. you will probably find best coeff. of coupling with
2-3 inches of sec. elevation above the flat primary plane.