Lee DeForest

What Lee DeForest did was to insert a third electrode, the grid or gate, in between the cathode (filament[?] or connected to the filament) and the anode (plate[?]) of the already invented diode. The resulting triode or three-electrode vacuum tube could be used as an amplifier for audio signals. The triode would be a good candidate for the most important innovation in electronics in the first half of the 20th century, between Guglielmo Marconi's progress in radio in the 1890s and the invention in 1948 of the transistor. The audion was patented with U.S. Patent No. 879,532.