What is vacuum tube
vacuum refers to a space where charged particles such as
electrons, protons, neutrons and all other matter are absent.
In other words, vacuum is nothing but the empty space.
tube is an electronic device that controls the flow of
electrons in a vacuum. It is also called as electron tube or
valve. John Ambrose Fleming developed the first vacuum tube in
1904. Fleming’s diode allows the flow of electric current in
only one direction (from cathode to anode) and blocks the
electric current in another direction (from anode to cathode).
In 1906, American electrical engineer Lee De Forest invented
Audion vacuum tube.
The invention of vacuum tubes has produced a new branch of engineering called electronics. In early days, vacuum tubes are used in television, radios, radar, electronic computers, and amplifiers. However, after the development of semiconductor devices, the usage of vacuum tubes in the electronic devices was reduced. Now-a-days, most of the electronic devices (computers, television, radar etc.) made from vacuum tubes are replaced by the semiconductor devices such as diodes, transistors, and integrated circuits.
Vacuum tubes are huge and occupy large amount of space.
However, the construction and operation of vacuum tubes is
easy to understand. Vacuum tubes are made from the materials
such as glass and ceramics. Vacuum tubes are mostly depends on
emission process to emit the free
electrons. In the thermionic process, heat is used to
emit the free electrons. Vacuum tube that emits the free
electrons by the application of heat is called thermionic
valve or thermionic tube.
A vacuum tube consists of cathode (also called as filament), anode (also called as plate), and electrode (also called as grid). Cathode is an electron emitter that emits the free electrons whereas anode is an electron collector that collects the free electrons.
Grid or electrode controls the electric current or flow of electrons between anode and cathode. The free electrons that are emitted by the cathode are attracted towards the anode or plate. These free electrons carry the electric current while moving from cathode to anode.
heated and indirectly heated cathode