Triode were invented, Philipp Lenard used the principle of grid control while conducting photoelectric experiments in 1902. The first vacuum tube used in radio was the thermionic diode or Fleming valve, invented by John Ambrose Fleming in 1904 as a detector for radio receivers. It was an evacuated glass bulb containing two electrodes, a heated filament and a plate (anode). Triodes came about in 1906 when American engineer Lee De Forest and Austrian physicist Robert von Lieben independently patented tubes that added a third electrode, a grid, between the filament and plate to control current. Von Lieben's partially-evacuated three-element tube, patented
Vienna valve trombone Vienna valve trombone Vienna valve trombones use Vienna Valves which were one of the earliest valve systems used in wind instruments. These valves were first publicly reported in 1815 and valved trombones were first introduced in the late 1830s. The Vienna valve was invented in Leipzig in 1821 by Sattler, predating the Perinet valve and rotary valve used in France and Germany (and in all French horns). The Vienna Valves (or Double Valves) have two short parallel pistons connected at the bottom by a bar that is moved by a long rod or linkage connected to the spring-loaded finger plate.