Originally developed for use for radio amateurs in 1920, the valve called triode of Audion RAC3, manufactured for american engineer Elman B. Mayers, showing the metal contacts for its setting in the circuit. To notice that this valve also takes the name of Audion. In the beginning thermoionic history in U.S.A., many had been the manufacturers of valves that they had bothered DeForest with its patent of 1907. Mayers was one of them and more developed this valve for ends of the radio-fanso of that professional transmission. It happens that for return of 1920 to all powerful RCA it took account of this market. The powerful Sarnoff, director of the RCA, through justice, ordered to arrest all those that do not pay license to manufacture valves. It did not give another one, Mayers an active engineer mounted its it manufactures about 15 km of the American border, in Canada, and started to sale its valves for order. Many had followed the steps of Mayers, using the same strategy and had been called in the thermoionic history as a independent manufacturer.