Although the vacuum tube was invented by John Ambrose Fleming, it was Thomas Edison who later discovered the "Edison effect," which states that electricity does not necessarily need a solid material to move through; it can move through gas or vacuums as well. Without this realization, vacuum tubes would never have been invented.
John Ambrose Fleming invented the first vacuum tube, the diode, in 1904. Lee De Forest invented the "audion" in 1906 (which was improved by others as the triode in 1908) and used in the first telephone amplifiers. Many other kinds were invented for various purposes.
The transistor became cheaper in the 1960s and was much smaller, worked on lower voltages, and used less power. In addition, unlike vacuum tubes, they were much less likely to be damaged by being dropped and had extremely long life. Eventually, they were also much cheaper than glass vacuum tubes. At this time, most radios, television sets, and amplifiers began using transistors instead. High powered electronics such as broadcasting transmitters were transistorized more slowly. Television receivers continued using the cathode ray tube until the mid-2000s.

License information: CC BY-SA 3.0 and GFDL
MPAA: G
Go to source: https://simple.wikipedia.org/wiki/Vacuum_tube