The term electronic tube in electronics means a device known as a vacuum tube, or a electron tube, or a thermionic valve, or a valve designed and constructed for the primary task of amplification, switching, modification, or creation of an electrical signal in a controlled environment where the movement of electrons take place in a low pressure space. This space does not have to be necessarily tubular in form. Devices or vacuum tubes largely known as soft valves are filled with gas under low pressure. The hard vacuum tube devices are constructed with internal gas pressure reduced to as far as possible. These devices depend on thermal emissions of electrons, and hence the term thermionic.
The history of the development of electronics technology leading to the development and commercialization of technologies has volumes to speak for these critical devices known as vacuum tubes. Radio broadcasting, television, radar, high fidelity sound reproduction, large telephone networks, digital computers, and industrial process control technologies have known vacuum tubes to be significantly critical devices during these widespread and practical developmental and commercialization stages.
Vacuum tubes have specialized applications in high power radio frequency transmitters, and in audio amplification, for reasons of engineering. Cathode ray tubes or CRT are popular display devices in televisions, video monitors, and oscilloscopes. The magnetron, another specialized form of the electron tube holds the claim to be the source of microwave energy in microwave ovens and in some radar systems.
0, 2, 1, 5, 6, 12, 25, and 50-volt heater / filament tubes, ECC, EL, KT, and numbered tubes are some types of vacuum tubes.