Topics Which Are Covered Here Are
1. Vacuum Tube And Its Working
2. Working Of Grid
3. How The Vacuum Tube Work As An Switching Device
Vacuum Tube And Its Working
All vacuum tube are made on the concept of Audion.
**The Audion is an electronic amplifying vacuum tube. It was the forerunner of the triode, in which the current from the filament to the plate was controlled by a third element, the grid. A small amount of power applied to the grid could control a larger current from the filament to the plate, allowing the Audion both to detect radio signals (that is, make them audible) and to provide amplification. However, Audion is quite distinct from the true vacuum triode in that it is not capable of linear amplification.
Electrons are emitted from cathod and passed through a grid or many grids. This grid controls the electron current. Electron then strike the anode and absorbed by it. Disigning the cathod, grid and the tube will make the AC signal voltage into a larger AC voltage, hence amplifying it.
**Todays transistor makes use of electric field in crystal.
Figure shows a typical modern vacuum tube. It is a glass bulb with wires passing through its bottom, and connecting to the various electrodes inside. Before the bulb is sealed, a powerful vacuum pump sucks all the air and gases out. This requires special pumps which can make very “hard” vacuums. To make a good tube, the pump must make a vacuum with no more than a millionth of the air pressure at sea level (one microTorr, in official technical jargon). The “harder” the vacuum, the better the tube will work and the longer it will last. Making an extremely hard vacuum in a tube is a lengthy process, so most modern tubes compromise at a level of vacuum that is adequate for the tube’s application.
Working Of GRIDS
The control grid is a piece of plated wire, wound around two soft-metal posts. In small tubes the plating is usually gold, and there are two posts made of soft copper. Grids in big power tubes are made up of tungsten or molybdenum wire welded into a basket form to absorbe heat. Some large power tubes use basket-shaped grids made of graphite.
Theis is an another term secondary emission,which is always avoided. This is caused by electrons striking a smooth metal surface. If many secondary electrons come out of the grid, it will lose control of the electron stream, so that the current “runs away”, and the tube destroys itself. So, the grid is often plated with a metal that is less prone to secondary emission, such as gold. Special surface finishing is also used to help prevent secondary emission.
Now The Question Arises, How The Vacuum Tube Helps In Computers?
Actually the magnification given by the grid to the voltage helps in switching on or off, which in turns creates that test tube as an virtual switching divece.