One of the earliest electronic instruments of the Soviet period, the Radio (or ‘Cathodic’) Harmonium was a three voice polyphonic cathode vacuum tube instrument controlled by a manual keyboard, designed for playing atonal music by the audio physicist Sergeĭ Nikolaevich Rzhevkin (1891-1981). The instrument was used by the philosopher Ivan Orlov in his investigations of aural phenomena.
‘A course of lectures on the theory of sound’ Sergeĭ Nikolaevich Rzhevkin. Pergamon Press, 1963
Orlov, I. E. 1926e. “Experiments with Rzhevkin’s cathode harmonium.”A Collection of Articles in Musical Acoustics (Russian),State Institute of Musical Science, 1925, 1.