In 1906 was vacuum tube invented.
Developed from Lee De Forest's 1906 Audion, a partial vacuum tube that added a grid electrode to the thermionic diode (Fleming valve), the triode was the first practical electronic amplifier and the ancestor of other types of vacuum tubes such as the tetrode and pentode.
The Audion (also called the De Forest valve, and since 1919 known as the triode) was a result of De Forest's interests in wireless telegraphy. It was invented in 1905, and in January 1906, De Forest filed a patent for diode vacuum tube detector. The Vacuum Tube of John Ambrose Fleming. Sir John Ambrose Fleming (1849–1945) was an English electrical engineer and physicist, known primarily for inventing in 1904 the first vacuum tube. It was also called a thermionic valve, vacuum diode, kenotron, thermionic tube, or Fleming valve.