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Re: Newbie Question- what toroid size?

Original poster: Steve Conner <steve@xxxxxxxxxxxx>

What!!  Are you saying that the resonant frequency is dependent only
on the wire length and the top load size has no effect???

Jared's Tesla coil design method consists of choosing a topload of the right capacitance to make the resonant frequency equal to the quarter wave resonance of the length of wire in your secondary. If you do that, then that is indeed also the right frequency to tune the primary circuit to.

However, most of us believe that there is absolutely nothing special about the quarter wave resonance frequency. You can use more topload than Jared's design method recommends, and if anything the performance is improved. Provided of course your power supply and capacitors can deliver enough energy to charge the bigger topload to its breakout voltage. If not, the performance may be unchanged or even get worse.

These days I like to choose the topload capacitance such as to make the characteristic impedance: sqrt(L/C) equal to about 50,000 to 100,000 ohms. If Terry's "220k+1pf/foot" thing is correct, then this gives the resonator a loaded "Q" of about 5 to 10, once you allow for the series to shunt transformation. (Terry's model uses a series R-C circuit, but the resistance that determines the Q is the equivalent shunt resistance.)

Matt: Alan Sharp and I have been running a mini Teslathon up here in Scotland recently. We call it R.F. Burns Night ;-)

Steve Conner