Nikola Teslas magnifying transmitter, a huge Tesla coil, in operation at his Colorado Springs laboratory in 1899-1900. The source says it generated around 12 million volts at a frequency of 100 kHz with an input power of 300 kilowatts. The "Century Magazine" article says: :"The ball shown in the photograph, covered with a polished metallic coating of twenty square feet of surface, represents a large reservoir of electricity, and the inverted tin pan underneath, with a sharp rim, a big opening through which the electricity can escape before filling the reservoir. The quantity of electricity set in movement is so great that, although most of it escapes through the rim of the pan or opening provided, the ball or reservoir is nevertheless alternately emptied and filled to over-flowing (as is evident from the discharge escaping on the top of the ball) one hundred and fifty thousand times per second."