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Spark-Gap Oscillator:
Tesla was central in establishing the 60 cycle alternating current power system still in use today. Yet he suspected that the more striking phenomena resided in the higher frequencies of electric vibration. To reach these heights, he first tried dynamos spun at higher speeds and having a greater number of poles than any that had existed before. One having as an armature a flat, radially grooved copper disk achieved 30,000 cycles, but Tesla wanted to go into the millions of cycles.
It occurred to him that this vibratory capability was to be found in the capacitor. With a capacitor circuit, the spark-gap oscillator, he did indeed achieve the higher frequencies, and he did so by non mechanical means. The circuit was promising enough for him to patent it as A Method of and Apparatus for Electrical Conversion and Distribution, for Tesla saw in it the possibility of a whole new system of electric lighting by means of high frequencies. Though it was quickly succeeded by the Tesla coil and is not numbered among the more famous of the lost inventions, the spark-gap oscillator is pivotal for Tesla as the invention that launched him into his career in high frequencies.
How it works:
The capacitor. There are only a few basic building blocks of electrical circuitry. The capacitor is one of them. Tesla didn't invent it, it had been around for some time, arguably for millennia, but he did improve upon it in three of his patents. Also called condenser, the common capacitor is just a sandwich of conductive and nonconductive layers that serves the purpose of storing electrical charge. The simplest capacitor has just two conductive sheets separated by a single sheet of insulation. In the capacitor shown, the conductive elements are two metal plates.
The insulation between them is oil. In the official vocabulary, the plates are indeed called plates and the insulative layer (oil, glass, mica, or whatever) is called the dielectric. Connect the two terminals of a capacitor into a circuit where there is plus-minus electrical potential, and charge builds on the plates, positive on one, negative on the other. Let this charge build for a while, and then connect the two plates through some resistance, a coil, say, and the capacitor discharges very suddenly. Tesla said, The explosion of dynamite is only the breath of a consumptive compared with its discharge. He went on to say that the capacitor is the means of producing the strongest current, the highest electrical pressure, the greatest commotion in the medium.
The capacitor's discharge is not necessarily a single event. If it discharges into a suitable resistance, there is a rush of current outward, then back again, as if it were bouncing off the resistance, then out, and back and so forth until it peters out. The discharge is oscillatory, a vibration. The vibration can be sustained by recharging the capacitor at appropriate intervals. When Tesla talks of the capacitor's discharge causing commotion in the medium, he means a vibration or mix of vibrations. The character of this vibration is determined in part by the capacity of the capacitor, that is, how much charge it will hold. This is a function of it size, the distance between plates, and the composition of the dielectric. Upon discharge there would be, typically, a fundamental vibration, some harmonics, and perhaps other commotion, maybe musical, maybe not. Additional circuitry can tame the vibration to a pure tone.
Source: https://altered-states.net/barry/tesla/ https://altered-states.net/barry/tesla/