The Audion Piano (1915) Lee De Forest

Lee De Forest (Born: August 26, 1873, Council Bluffs, Iowa. Died June 30, 1961 ) , The self styled "Father Of Radio" ( the title of his 1950 autobiography) inventor and holder of over 300 patents, invented the triode electronic valve or 'Audion valve' in 1906- a much more sensitive development of John A. Fleming's diode valve. The immediate application of De Forest's triode valve was in the emerging radio technology of which De Forest was a tenacious promoter, De Forest also discovered that the valve was also capable of creating audio frequencies using the heterodyning/beat frequency technique: combining two high frequency signals to create a composite lower frequency within audible range.

Lee De Forest's Triode Valve of 1906

De Forest Created the 'Audion Piano', the first vacuum tube instrument in 1915. The Audion Piano was a simple keyboard instrument but was the first to use a beat-frequency (heterodyning) oscillator system and body capacitance to control pitch and timbre ( The heterodyning effect was later exploited by the Leon Termen with his Theremin series of instruments and Maurice Martenot's Ondes-Martenot amongst others. ). The Audio Piano used a single triode valve per octave which were controlled by a set of keys allowing one note to be played per octave. The output of the instrument was sent to a set of speakers that could be placed around a room giving the sound a dimensional effect. De Forest planned a later version of the instrument that would have separate valves per key allowing full polyphony- it is not known if this instrument was ever constructed. De Forest described the Audio Piano as capable of producing:  "Sounds resembling a violin, Cello, Woodwind, muted brass and other sounds resembling nothing ever heard from an orchestra or by the human ear up to that time - of the sort now often heard in nerve racking maniacal cacophonies of a lunatic swingband. Such tones led me to dub my new instrument the 'Squawk-a-phone'."  (Lee De Forest Autobiography "The Father Of Radio" 1915. P331-332)  "The Pitch of the notes is very easily regulated by changing the capacity or the inductance in the circuits, which can be easily effected by a sliding contact or simply by turning the knob of a condenser. In fact, the pitch of the notes can be changed by merely putting the finger on certain parts of the circuit. In this way very weird and beautiful effects can easily be obtained." De Forest, the tireless promoter, demonstrated his electronic instrument around the New York area at public events alongside fund raising spectacles of his radio technology. These events were often criticised and ridiculed by his peers and led to a famous trial where De Forest was accused of misleading the public for his own ends:  "De Forest has said in many newspapers and over his signature that it would be possible to transmit human voice across the Atlantic before many years. Based on these absurd and deliberately misleading statements, the misguided public ... has been persuaded to purchase stock in his company. "  De Forest also collaborated with a skeptical Thadeus Cahill in broadcasting early concerts of the Telharmonium using his radio transmitters (1907). Cahill's insistence on using the telephone wire network to broadcast his electronic music was a major factor in the demise of the Telharmonium.  Vacuum tube technology was to dominate electronic instrument design until the invention of transistors in the 1960s. The Triode amplifier also freed electronic instruments from having to use the telephone system as a means of amplifying the signal.

Lee De Forest in 1948

Further Information: Lee De Forest "Father Of Radio" (Autobiography).