Before the invention of the transistor, for almost half a century from the beginning of the 1900's, radios as well as many other electronic devises were basically valve sets. It was John Ambrose Fleming who invented the diode or thermionic valve.

Fleming was born in Lancaster in 1849. He studied under the famous James Clerk Maxwell and then worked as a researcher and professor of electrical engineering in Cambridge, Nottingham and London. He also invented the right-hand rule of electromagnetism.

In 1899, at the age of fifty, Fleming was already a famous scientist. He accepted Marconi's proposal to work with him and became his scientific consultant. He was immediately involved in the technical breakthrough that many people thought impossible – the wireless transmission across the Atlantic Ocean. Fleming played a key role in planning the stations that allowed Marconi, on 12 December 1901, to establish his historic wireless connection across the Atlantic.

The relationship between Marconi and Fleming continued for years and although they did not always get along very well Marconi never interfered with Fleming's personal research. In 1904 Fleming devised the first prototype thermionic valve. Although its application was not yet clear, Marconi decided to produce it as a new electromagnetic detector in his Chelmsford factory.

Marconi’s Nobel lecture held at the Swedish Royal Academy proves how much he trusted and valued Fleming. When talking about the development of his experiments, Marconi cited a long extract from Fleming’s book The Principles of Electric Wave Telegraphy, published in London in 1906. He referred to the book several times and also recalled Fleming’s contribution to the transatlantic adventure. Marconi held Fleming in great esteem, even though they had different opinions – for instance on the relationship between daylight and wavelength.

Fleming worked as a scientific consultant for the Marconi Company until 1931 and died aged ninety-six in 1945.

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