The essential difference between a Tesla coil and all the others, such as
ignition coils, is that the Tesla coil is designed to makes full use of a
high coil Q.

Coil Q = Coil Reactance / resistance.

i.e., it makes use of the resonant rise in volts across a tuned circuit with
high inductance, low (self) capacitance and low resistance.

It has to be physically large to obtain a low wire resistance combined with
a high inductance of many turns. In addition, of course, the large physical
size enables very high voltages without flash-over.

Optimum resonant frequencies (very non-critical) for home constructors are
between 50 and 150 KHz. The lower the frequency the higher the voltage. Use
a ball or a thick ring on the top to minimise corona discharge.

It's as simple as that. I hope this description will enable you to make
your own Tesla coils. But in this day and age they are mainly of educational
and entertainment value. Perhaps they always were. Tesla was a
flashing-light with bangs, circus showman without knowing exactly what he
was doing.

Ingenious nevertheless. But perhaps not quite in the same class as Edison.
Even Edison and people like Marconi did not know exactly what they were
about.

But we should be very grateful to the few workers, the willing slaves of
technology, between 1880 and 1905 who dragged the human race, often at great
personal disadvantage and expense to themselves, away from the feudal age
into the present age of electronics.

The $64,000 question : what is the human race, you stupid set of succeeding
genocidal suckers, to do with your rich inheritance?

Too late to ask Tesla.
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Reg, G4FGQ