Vacuum Tube (Electron Tube), refers to evacuate the inside glass bottles, in order to facilitate the free electrons flow, can also be effective to reduce the oxidation loss of the filament.
(1) According to the heating methods
Vacuum tube can be divided into two major categories, direct thermal and thermal side.
Direct thermal vacuum tube was an early birth. It has a fatal flaw, is vulnerable to the cathode filament temperature to change characteristics. When the filament voltage fluctuation, or when the AC power supply to the filament, the cathode present in the unstable state.
Indirectly heated vacuum tube workmanship relatively stable. As the volume and the heat reservoir of metal sleeve is much greater than the conventional filament. Even the filament temperature temporarily changes, and even a few seconds of heating is stopped temporarily, the temperature change of the metal plate is limited.
(2) According to container structures
Most commercially available vacuum tube, whose wall is made of glass. And, compared with military and other special types are made of metal.
(3) According to the structure and use
Vacuum tube can be divided into diodes, transistors, tetrode, quadrupole bundle ray tube, pentode and composite pipe etc.
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