A sealed enclosure, either highly evacuated or containing a controlled quantity of gas, in which electrons can be made sufficiently mobile to act as the principal carriers of current between at least one pair of electrodes.
A sealed tube, usually of glass, containing a vacuum or a gas and electrodes that are connected to pinlike terminals that protrude from the base, used as a plug-in component in an electronic device to control the flow of electrons.
A sealed glass tube containing either a vacuum or a small amount of gas, in which electrons move from a negatively charged electrode, the cathode , to a positively charged one, the anode . The cathode is usually heated by an electric current to free the electrons. Other electrodes in the tube can vary the electric or magnetic fields in the tube to control the strength and direction of the moving electrons. Electron tubes are used to amplify signals, rectify AC currents, and produce x-rays, among other uses. They have been mostly replaced by transistors but are still used in television screens, computer monitors, and microwave technology.