Amplifiers are not only a fundamental component of radios, televisions and telephones, they are essential to all modern electronics. Amplifiers differ considerably in design and in the amount of amplification (called gain) they produce, but they all work in much the same way.

The evolution of the amplifier began with Thomas Alva Edison who, in the process of studying his direct current light bulbs, inserted a metal plate near the filament. He discovered that electricity would flow from the positive side to the plate, diode, but treated it as curiosity.

John Ambrose Fleming, who worked for Edison, modified the diode in 1904 to detect radio waves. The Englishman called his invention the thermionic valve because it controlled the flow of water, but in the United States, it was called a vacuum tube, which better described its construction.

In 1906, American scientist Lee de Forest added a third element, called a...