Original poster: "Dr. Resonance" <resonance@xxxxxxxxxx> Mike --- the easiest way is to take some "scrap" 12 AWG solid wire ---enough for approx 24 turns to make a "test primary". Eight cardboard strips are cut 1 inch wide x 12 inches long and a razor knife is used to cut small slits in the edge of the cardboard. The cardboard is tacked to a scrap plywood base using hot glue (very fast). The wire is pushed into the strips forming a 24 turn test primary. Every turn scrape a bare spot in the insulation to attach your primary tap. Stagger these bare spots approx 3/4 inch so they don't all line up in a straight line.
Start at approx 3 turns and keep your variac around 30-40% and set your total primary sparkgap distance to 0.120 inches (120 mils). Move outward on the taps until you the the primary resonance point.
In this manner you can "test tune" with a "scrap wire" primary which you can assemble in approx 30 minutes. It doesn't have to look fancy at all --- just provides for a quick and fast tuning method until you find the best point. Later, wind your 1/4 inch copper tubing (or Home Depot #6 AWG bare ground wire) primary adding appox 2 turns beyond your "test primary" findings to add for any additional adjustment in tuning.
It's fast, easy, and a good way to test tune any coil system. When in tune move the sec coil up and down in 1/2 inch increments to adjust for the best coeff. of coupling --- sometimes the sec will produce best sparks elevated 2-3 inches above the horizontal plane of the primary coil.
After all these test tuning is finished, then open up your spark gap to 0.250 inches total and bring your variac up to full power. With the larger sparks and larger ion cloud you might need to adjust the primary tap out 1/2 turn or less to adjust for the additional topload capacitance produced by the longer sparks which will lower the resonant freq slightly.
Dr. Resonance
Original poster: "Mike Tucknott" <michael.tucknott@xxxxxxxxxx> Hi Guys It`s been some time since I had to work this stuff out and I`m stumped I know most of the coil paramiters but not the primary inductance OK The coil is:-12 1/2" by 61" using 18AWG wire with a 6" by 28" top load the frequency is 64.73 KHzI`m using 0.02 uF of primary cap. So how much inductance do I need on the primary to get the system to tune. I`v used a few PC programs but the figures are out of there range. HELP Cheers Mike Tucknott Smokin in south Oxfordshire UK <http://freespace.virgin.net/michael.tucknott/tesla.htm>http://freespace.virgin.net/michael.tucknott/tesla.htm