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A vacuum tube amplifier is a device that employs vacuum tubes, which are also sometimes called electron tubes and thermionic valves, to amplify the power, or amplitude, of an electronic signal. This term is usually applied to audio components although a vacuum tube amplifier can be designed and used for other applications such as radar and broadcasting. A typical audio vacuum tube amplifier takes a low level audio input signal and amplifies it, making the resulting signal available to speakers or headphones.
In the United States, vacuum tubes are usually called "tubes" or "valves," and these terms are used interchangeably when discussing electronics, especially audio components. Vacuum tubes were an important part of all early electronics devices until they were supplanted by solid state devices, particularly the transistor. A vacuum tube is a glass tube with a design that is similar to the light bulb. Current is fed into the tube, which has had all air evacuated and is under vacuum, and goes through a filament which gives off electrons. Vacuum tubes can be configured in a number of ways for different purposes besides amplification such as switching and rectification functions.
The first mass produced audio signal amplifiers were vacuum tube amplifiers. By taking an audio input signal and using standard wall current or other electrical current input, the vacuum tubes significantly strengthen the audio signal — as much as thousands of times. By the 1960s and 1970s, advances in electronics allowed for solid state amplifier designs which were cheaper to produce, required less space, and needed no vacuum tubes which sometimes burn out and require replacement.
Audiophiles and musicians, however, noticed a difference in the sound produced by the two types of amplifiers, creating a debate which has continued to this day. Many claim that the sound produced by a vacuum tube amplifier has certain qualities that sound from solid state amplifiers lack and insist that tube amplifier sound is richer and "softer," resulting in a more pleasing listening experience. This assertion is dismissed by some experts and consumers and the difference seems to be a matter of taste. Although the advent of solid state designs made vacuum tube amplifiers technologically obsolete, manufacturers continue to produce vacuum tube amplifiers to meet the demands of those willing to pay the increased cost for such components. A home built vacuum tube amplifier is also a popular subject for hobbyists and audio and electronics enthusiasts.