Vacuum tube (or also called valve in Great Britan) is electronic component / device used in audio industry mainly as amplification component before transistors were found.

While transistors are cheaper and more effective with longer lifetime, vacuum tubes are very popular until today and preferred by many audiophiles from hi-end listening rooms (vacuum tube amps) to professional recording / mixing studios (equalizers, preamps, compressors and warming devices).

The type of vacuum tube known as a thermionic tube / valve uses the phenomenon of thermionic emission of electrons from a hot cathode (electrons are emitted in vacuum tube space of glass tube) with use of heater supply (that is why tube is glowing) and is used for a number of fundamental electronic functions such as signal amplification.

Thanks to heather inside tube not just vacuum tube is hot, but also sound is significantly warmer. Signal is not going thru wires but thru vacuum tube "space” and electrons are "flying” from hot cathode (warmed with heater) to anode – where amplified signal is received.

This phenomenon affect signal / sound in way appreciated by audiophiles – transients and trebles are not so sharp – they are smoother, rounder and more pleasant to ears, signal is saturated – bass is fatter and warmer, mids and trebles are colored.

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