A vacuum tube also called a valve in British English is an electronic device used in many older model radios, television sets, and amplifiers. Vacuum tubes produce a lot of heat as they have a filament like a light bulb, and being made of glass they are fragile and can break. Vacuum tubes were used in the first computers like the ENIAC, which demanded lots of work because of the heat it produced.
History[change | change source]
Although the vacuum tube was invented by John Ambrose Fleming later, it was Thomas Edison who discovered the “Edison effect”. The Edison effect 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.
Current uses[change | change source]
In the 21st century, vacuum tubes are rarely used in common electronic equipment. Many devices today rely on the transistor over the vacuum tube. Some devices that still use the vacuum tube, however, include:
There are still a few applications that use vacuum tubes:
- Systems which need high frequency operation, high-power output or very high amplification, such as television transmission, X-ray machines, radar, and microwave ovens.
- People who enjoy listening to music on high-quality home stereo systems sometimes buy amplifiers which use vacuum tubes. (See tube sound).
- Musicians who play electric musical instruments such as electric guitar sometimes use vacuum tube amplifiers.