Cunningham Audio-Tron Tubular Vacuum Tube, ca. 1916

Elmer T. Cunningham produced this tubular double filament triode vacuum tube, which he called an "Audio Tron," around 1916 at his Audio Tron Sales Company in San Francisco. Cunningham started the company in 1915, without patent rights, to compete with Lee de Forest's spherical Audion. His tubular double-sided design allowed dual filaments, providing longer operating life. Produced in large numbers, and more dependable than the Audion in quality, the Audio Tron contributed to the rise in amateur radio interest and provoked de Forest to devise his own tubular audion. A 1916 De Forest suit against Cunningham was settled out of court, but Cunningham continued to produce the Audio Tron and soon after, Otis Moorhead of San Francisco also began marketing his own Electron Relay Tube, similar to the Audio Tron. The competition created a price war, severely affecting de Forest's business. Cunningham, whose business was aimed largely at amateurs, temporarily discontinued production during World War I. Today he is remembered as the most successful of the tube counterfeiters, flaunting both Fleming's and de Forest's vacuum tube patents (1915-1920). Aggressive both in marketing and in the courtroom, Cunningham, unlike Moorhead or de Forest, not only was financially successful but won concessions from powerful RCA, who decided to buy his company rather than fight him.