I've built various Tesla coils over the years. The prospect of there being
an overlooked aspect to the arrangement and tuning of the circuit is quite
interesting.
Up to the time of experimenting with his high frequency spark gap
oscillators, Tesla had only ever witnessed high output voltages in the low
kilohertz frequency range, as produced by his high frequency alternators.
He would have been amazed, as anyone, at the initial unexpected
characteristic of high voltage at high and very high frequencies. As we all
know, a spark gap oscillator can be driven with either a DC or AC supply.
Either method results in an AC oscillation in the final stage of the
amplifier. The suggestion that Tesla was capable of effectively creating a
pulsed (or impulsed) DC output on his secondaries is intriguing.
We know that Tesla used various means to quench the spark gap, all directed
towards creating short duration impuses which increase the efficiency of
the oscillator. An early method was to employ a powerful magnet at the
spark gap, as mentioned. The rotary spark gap is the most commonly used
method for large coils at relatively high power levels.