What device was used to amplify electrical signals before the invention of the transistor?

Fragile vacuum tubes were used to amplify and switch electrical signals before the invention of the transistor. Vacuum tubes were a basic component for electronics throughout the first half of the twentieth century when they were invented in 1904 by John Ambrose Fleming.

Vacuum tubes were used with devices such as radio, television, radar, sound reinforcement, sound recording and reproduction, large telephone networks, analog and digital computers, and industrial process control units. These specific tubes were the foundation for many scientific discoveries and technical innovations which are now found in modern electronic technology.

Beginning in the 1950s, solid-state devices (transistors) gradually replaced vacuum tubes.

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