Electronic amplifiers make a signal from the radio or electric instrument louder and stronger by using transistors or vacuum tubes. Electronic amplifiers have to be connected to electrical current or a battery to work. Once the signal from the radio or electric instrument has been made louder and stronger, the signal needs to be connected to a loudspeaker so that people can hear it.
When an amplifier tries to make the sound louder than it can, it adds distortion to the sound. Some amplifiers are made to add controlled distortion. Distortion from transistors sounds different than distortion from tubes. Distortion from tubes is often said to be more musical. Because of all this, more expensive amplifiers often add controlled distortion with tubes. Many of these amplifiers use transistors for a "clean" sound (without distortion).
From the 1920s until the 1950s, electronic amplifiers used vacuum tubes. However, electronic amplifiers with vacuum tubes were heavy, and they produced a lot of heat. They also broke down a lot.
Since the 1960s, most electronic amplifiers have been built with transistors. Transistors are lighter, cheaper, and more reliable.

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