Tesla Colorado Springs lab-12 million volts
Nikola Teslas magnifying transmitter, a huge Tesla coil, in operation at his Colorado Springs laboratory in 1899-1900. Part of a photo shoot by photographer Dickenson V. Alley to accompany Tesla's June 1900 article in Century Magazine, "The Problem of Increasing Human Energy".
The apparatus consisted of a 60 foot diameter Tesla transformer around the periphery of the room consisting of a one-turn primary winding and a 50 turn secondary wound on a 8 ft high wooden "fence" around the room (visible dimly in the background). The primary was connected to a bank of 13 oil capacitors and excited by current from a 20 to 40 kV step-up transformer from the power line through a rotary spark-gap interrupter. One end of the secondary winding was grounded and the other end was connected to the 20 ft diameter 100 turn coil in the center of the picture, called the "extra" or "resonator" coil. This third coil is not magnetically coupled with the others and produced the high voltage output by resonance with its own parasitic capacitance. The high voltage terminal at the top of the coil is attached to a vertical telescoping boom with a 30 inch metal sphere at the top which could be raised into the sky through a hatch in the roof. Note the luminous corona discharge visible along the wire connecting the secondary winding with the resonator coil, left. The accompanying text in the Cohen article said:
In Fig. 1 we see the Tesla oscillator in full operation at 12 million volts and a frequency of one hundred thousand (Hz). The flame-like discharge measures 65 feet across. This experiment was made to show how the nitrogen of the atmosphere could be made to combine with the oxygen. The wire cage (coil) measured 20 feet in diameter and 30 feet in height. This is not the actual coil which is excited by the primary of the Tesla transformer, but a separate coil which is attuned to a certain frequency of the secondary. This is apparent by noting the large circular fence-like wall in the rear, which measures 60 feet in diameter and is wound with heavy copper wire. The primary is embedded in the ground and connected to the oscillating circuit, comprising the high tension oil condensers and the inductance in the primary, and the spark discharger. In all these experiments the primary of the low-tension transformer was excited with 300 kilowatts of electrical energy.