Vacuum Tubes or Electron Tubes:
Vacuum Tubes or Electron Tubes, Diode, triode, Tetrad, and Pentode– Vacuum tube is a device through which the flow of current in a circuit is controlled. There are various types of vacuum tubes (e.g. diode, triode, tetrad and pentode etc.) and these various forms of vacuum tubes are used as switches, amplifiers and oscillators etc. Basically, a vacuum tube consists of a closed envelope of glass with electrodes fixed on its inner side. Glass envelope is fixed on a strong base and terminals have been pulled out from the electrodes which are fitted inside the tubes. The air has completely been pushed out of the tube at the time it is being manufactured, due to which a vacuum develops inside the tube, for preservation of which the tube is sealed properly.
The forms of vacuum tubes depend on the quantity and structure of electrodes present inside the tube, (i.e. name of tube is given on the basis of quantity of electrodes present in it). There are 2, 3, 4, and 5 electrodes respectively in diode, triode, tetrad and pentode. Two of the electrodes are common in every vacuum tube. These are called anode and cathode. There is a control grid in the triode apart from these two electrodes too. Electrons are emitted from cathode; therefore, these are called emitters. Whereas anode collects these emitted electrons, that’s the reason it is called collector. The function of the grid is to control the flow of electrons.
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