English: Schematic diagram of the circuit of the "magnifying transmitter", a Tesla coil circuit invented by Serbian-American engineer Nikola Tesla in the 1890s. It differs from ordinary two-coil Tesla coil circuits in that Tesla has added a third coil (L3) attached to the high voltage end of the secondary (L2), which is not magnetically coupled to the other two coils. This acts as a tuned circuit, resonating with its own parasitic capacitance (C2) to generate higher voltage. Tesla used this design 1899-1900 in the huge magnifying transmitter at his Colorado Springs laboratory, one of the largest Tesla coils ever built. With an input power of 150 kW it could produce potentials in the neighborhood of 12 million volts at a frequency around 150 kHz, creating 140 ft. bolts of "lightning". Circuit from Sarkar, Mailloux, Oliner, Salazar-Palma, Sengupta, (2006) History of Wireless, John Wiley and Sons, p. 279, fig. 8 on Google Books