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 The Vienna system was in common use in Germany on all kinds of instruments including trumpets up to 1850. Adolph Sax invented instruments with 6 independent valves 3 for each hand, but only the most dexterous musicians were able to play them. The valve trombone has definite advantages over the more common slide trombone, such as taking up less room in a seated orchestra. Verdi, for example, composed passages that would have been impossible on a normal slide trombone. For illustrations of a Vienna valve trombone c.1850, see: Vienna valve trombone Vienna valve trombones use Vienna Valves which were one