- Hugh Davies
Electronic keyboard instrument (not a piano) developed by Lee de Forest (b Council Bluffs, IA, 26 Aug 1873; d Hollywood, CA, 30 June 1961) in New York from 1915. De Forest introduced his Audion triode valve (vacuum tube) in 1906. A more sensitive development of John A. Fleming’s diode valve, it was to prove a major step in the development of electronics, especially radio. About 1915, while devising an electronic oscillator based on the valve, he discovered that it created an audible frequency that could be changed by holding the hand close to or touching certain parts of a circuit (the principle on which the theremin and Ondes Martenot are based). This led to the development of the Audion piano, the first vacuum-tube instrument, and the first to use a beat-frequency or ‘heterodyning’ oscillator system as well as to use body capacitance to control pitch and timbre. A prototype, using one triode valve per octave, permitted the playing of only a single note at a time within each octave. The output was heard through loudspeakers that could be placed for a stereophonic effect. A planned polyphonic version was to allocate a separate oscillator for each note, but because at that time de Forest’s Audion valves were unreliable and unstable, it seems that he was unable to complete a working instrument. De Forest’s French patent of ...