Define Vacuum Tubes?
What is Vacuum Tube?
Generally, vacuum alludes to a space where charged particles, such as, electrons, protons, neutrons and any remaining matter are missing. As such, vacuum is only the unfilled space.
Vacuum tube is an electronic gadget that controls the flow of electrons in a vacuum. It is also called as electron tube or valve. John Ambrose Fleming developed the primary vacuum tube in 1904. Fleming’s diode permits the flow of electric current in just a single direction (from cathode to anode) and blocks the electric current toward another direction (from anode to cathode). In 1906, American electrical engineer Lee De Forest created Audion vacuum tube.
The development of vacuum tubes has produced another part of engineering called electronics. In early days, vacuum tubes are utilized or used in TV, radios, radar, electronic PCs, and speakers. However, after the advancement of semiconductor devices, the utilization of vacuum tubes in the electronic gadgets was decreased. Presently a-days, the vast majority of the electronic gadgets (PCs, TV, radar and so on) produced using vacuum tubes are replaced by the semiconductor gadgets like diodes, transistors, and integrated circuits.
Vacuum tubes are huge and occupy large amount of space. However, the development and operation of vacuum tubes is easy to understand. Vacuum tubes are made using the materials like glass and ceramics. Vacuum tubes are generally relies or depends upon the thermionic emission process to emit the free electrons. In the thermionic process, heat is utilized to emit the free electrons. Vacuum tube that emits the free electrons by the use of heat is called thermionic valve or thermionic tube.
A vacuum tube comprises of cathode (additionally called as filament), anode (also called as plate), and electrode (also called as grid). Cathode is an electron producer that emits the free electrons though anode is an electron collector that collects the free electrons.
Grid or electrode controls the electric current or stream of electrons among anode and cathode. The free electrons that are emitted by the cathode are drawn in towards the anode or plate. These free electrons convey the electric current while moving from cathode to anode.
Directly heated and indirectly heated cathode
In the thermionic tubes, the cathode is heated electrically to an ideal temperature to emit the free electrons from the metal surface. This should be possible in two ways: by directly heating the cathode or indirectly warming the cathode.
If the heat or heating electric current is passed directly to the cathode that emits the free electrons, the cathode is supposed to be a directly heated cathode or directly heated emitter. In the directly heated cathode, the actual cathode is the warming heating or filament. Hence, the heat required to emit the free electrons from the metal surface is less contrasted to the indirectly heated cathode.
Assuming the heat or heating electric current is passed by indirectly to a cathode that emits the free electrons, the cathode is supposed to be an indirectly heated cathode or indirectly heated emitter.
In the indirectly heated cathode, there is no electrical connection between the cathode and the heater. Subsequently, the actual cathode isn’t a heating element or component. The heating electric current is gone through the heater or filament and the cathode is heated indirectly. Henceforth, how much heat required to discharge or emit the free electrons from the metal surface is more compared to the directly heated cathode.
Types of vacuum tubes
Vacuum tubes are generally classified into four types:
Advantages and disadvantages of vacuum tubes
Advantages of vacuum tubes
- Vacuum tubes are supplanted without any problem.
- Vacuum tubes can works at high temperature with no harm.
- Vacuum tubes produce predominant sound quality.
Disadvantages of Vacuum Tubes
- Vacuum tubes are tremendous contrasted with the semiconductor devices like diodes, semiconductors, and integrated circuits.
- Vacuum tubes produce more heat.
- High voltages are expected to work the vacuum tubes.
- Vacuum tubes consume more power.
- Significant expense.
- Failure rate is high.
- Vacuum tubes consume more space than the transistors.