An electronic device that controls the flow of electrons in a vacuum. It is used as a switch, amplifier or display screen. Used as on/off switches, they allowed the first computers to perform digital computations. Although vacuum tubes have made a comeback in high-end stereo components, most vacuum tubes today are the picture tubes (CRTs) in monitors and TVs. See vacuum tube types, audiophile and tube amplifier.
Early Vacuum Tube
Early vacuum tubes were used to amplify signals for radio and other audio devices. This one was made in 1915. Tubes were not used as switches in calculating machines until 1939. (Image courtesy of AT&T.)
Tubes in the 21st Century
Flat panels replaced tubes for TVs and monitors, but tubes are not obsolete. Many audiophiles swear they amplify music better than transistors, and who wouldn't be delighted with all 212 pounds of these Model One units designed by legendary audio engineer Mark Levinson.
Vacuum tubes have come in myriad shapes and sizes over the years, and the Vintage Radio and Communications Museum has one of the finest collections. (Images courtesy of Vintage Radio and Communications Museum of Connecticut, www.vrcmct.org)