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Re: spark gap

Original poster: "resonance" <resonance@xxxxxxxxxxxx>

The number of tubes in the gap depends on the xmfr current not the xmfr voltage. For a 20 to 30 mA nst, a typical stationary type spark gap would have 3 gaps so you end up using 4 tubes x 3 inches long each --- usually inside of a 6 inch long x 3 inch ID PVC tube. The extra room on one end allows for the 90 degree metal mounting tabs on the tube.

During initial tuning, set your TOTAL spark gap to 0.150 inches (150 mils). Keep the variac setting to 30-40% max while finding the resonant point. After it's in tune then you can go to a max gap value of 0.220 to 0.240 inches (220 to 240 mils) and bring the variac up to 100% power level.

I'm sending you some photos off-list of a typical copper pipe gap. This is a larger element gap for a 60 mA xmfr but you will get the idea for your 3 inch ID PVC tube. We use brass fasteners that so thru slightly slitted (don't overdo it here) holes to allow parallel adjust of all the pipes. The holes thru the PVC tube are just slightly larger than the fasteners. The copper pipe is tapped for a standard 1/4-20 NC brass machine screw.

Have fun with your coil.

Dr. Resonance

Original poster: mark@xxxxxxxxxxxxxxxx
Can someone point me in the right direction for working out the gap for my spark
gap ???

I'm using a 15Kv 20ma NST with a cap of about 0.0042uF, I'm planning on using a
piece of off cut 3" acyrlic pipe with 3/4" copper pipes bolted around the
inside, however am at a loss on how to check this is feasible and what sort of
gap I should leave between each pipe.