A vaccum tube is an evacuated electron conducting chamber (tube) designed to eliminate or minimize the influence of atmospheric gas. More commonly, a vacuum tube is an electronic mechanism used primarily to convert alternating current into direct current.

The vacuum tube consists of a glass encasement and two or more electrodes between which electrons flow freely. One of these electrodes, called the cathode, consists of a filament heated to the degree that it releases electrons, a process called thermionic emission. The other electrode, called the anode, consists of a metal plate attached to a filament. The electrons released by the cathode are attracted to the anode when the anode is positively charged, thus completing an electrical circuit. However, the electrons will not flow to the anode during the phase in an alternating current when the anode is negatively charged. In constructing the vacuum tube, all air...