The electron tube was developed in 1904 by the English physicist John Ambrose Fleming. While looking for an improved method to detect radio waves, Fleming discovered that the so called “Edison-effect” could be used for this. On the 6th of November 1904, he was applying for a patent in England called “Oscillation Valve” (a rectifying tube).
In 1906, US-American inventor Lee de Forest added a third electrode, the “control grid”. This triode allowed amplification of electronic signals for the first time.