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Transistors and thermionic valves

Updated Tuesday, 3rd August 1999

Without the valve and the transistor there would be no radio, no television and no computers. How did these vital inventions come about?

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Valves glowing with heat

John Ambrose Fleming invented the thermionic valve in 1904. It was the discovery that the electron was a particle that made this invention possible. So, what is a valve? Well, just like a tap in the water system, a valve will only let electricity flow one way and you can turn it on and off.

But that is where the analogy ends. The valve was useful as an electronic switch and its first use was in radio circuits detecting signals. The valve has two elements - a wire and a metal plate surrounded by a vacuum. The electricity flows between them.

Lee de Forrest added a third element to this valve to produce the triode, which allows far greater control of the electrical current. It could even provide a small amount of amplification: making a weak signal stronger.

It was this that made the future of the triode secure. AT&T improved on this idea by pumping out more air to make a better vacuum. And so the first practical electronic amplifier was born.


For the first time speech, radio and television signal could be boosted and the transmission of these mediums became world-wide throughout the Thirties and Forties. The valve was enormously successful but despite improvements it was always bulky, high on power and unreliable. The engineers dreamed of electronic devices that didn’t need a vacuum or a heater.


It was the invention of the transistor by Bardeen, Brattain and Shockley in 1947 that made possible the dominance of digital computers and hence much of our modern communication. This time it is the fact that electrons behave like waves that made the discovery possible.

In the years following its creation, the tiny, reliable transistor replaced the bulky and less reliable vacuum tubes that had been used to amplify and switch signals. The transistor lead eventually to the creation of integrated circuits that contained millions of small electrical components and was the foundation of modern electronics.


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