Transistor and how it works

Why can transistor radio valves be so small?
Transistor radio valves can be small because they are made with a class of material called semi-conductors.

In the early days of radio it was essential to have a rectifier, a component which allowed an electric current to flow with a low resistance in one direction and a high resistance in the opposite direction. This involved the use of a piece of carborundum crystal and a steel point.

Then a diode-valve was used as a rectifier. This consisted of two separated metals in a vacuum. They were contained in a thin glass tube, two inches long and one inch in diameter. More progress was made by the discovery of materials with an electrical resistance between high-value insulators and low-value substances such as plastic materials, now widely used in industry and called semi-conductors, are silicon, a non-metallic element and germanium, a metallic element.

Only a small amount of the elements is required and only a few volts are needed to carry the current. By a special industrial melting process, these semi-conductors can be joined together in layers like a sandwich. A transistor is basically a sandwich of three layers of semi-conductors, and it is possible to obtain several combinations.

Since the resistance of all semi-conductors is sensitive to light, the sandwich is housed in a sealed capsule and coated with black lacquer.

Transistors can be any size from a grain of rice to ¼ inch long. They can perform many of the functions of multi-electrode valves, need only a small voltage battery, are less liable to breakage, are considerably cheaper to produce and can be very much smaller.