vacuum tube(redirected from Firefet)
Also found in: Dictionary, Thesaurus, Encyclopedia.
a glass tube from which the air has been removed, containing two or more electrodes, between which passes an electrical current or spark; used in the production of x-rays, or to control circuits. Previously in wide use, the vacuum tube has been supplanted by transistors in electronic circuits.
A vessel of insulating material (usually glass) that is sealed and has a vacuum sufficiently high to permit the free flow of electrons between the electrodes that extend into the tube from the outside. In England, it is called a vacuum valve.