Valve audio amplifier

A valve audio amplifier (UK) or vacuum tube audio amplifier (United States) is a valve amplifier used for sound reinforcement, sound recording and reproduction.

Until the invention of solid state devices such as the transistor, all electronic amplification was produced by valve (tube) amplifiers. While solid-state devices prevail in most audio amplifiers today, valve audio amplifiers are still used where their audible characteristics are considered pleasing, for example in music performance or music reproduction.

Valve amplifiers for guitars (and to a lesser degree vocals and other applications) have different purposes from those of hi-fi amplifiers. The purpose is not necessarily to reproduce sound as accurately as possible, but rather to fulfill the musician's concept of what the sound should be. For example, distortion is almost universally considered undesirable in hi-fi amplifiers but may be considered a desirable characteristic in performance.

Small signal circuits are often deliberately designed to have very high gain, driving the signal far outside the linear range of the tube circuit, to deliberately generate large amounts of harmonic distortion. The distortion and overdrive characteristics of valves are quite different from transistors (not least the amount of voltage headroom available in a typical circuit) and this results in a distinctive sound. Amplifiers for such performance applications typically retain tone and filter circuits that have largely disappeared from modern hi-fi products. Amplifiers for guitars in particular may also include a number of "effects" functions.

The electric guitar originates from Rickenbacker in the 1930s but its modern form was popularised by Fender and Gibson (notably the Fender Telecaster (1951) & (1954) and Gibson Les Paul (1952) during the 1950s. The earliest guitar amplifiers were probably audio amplifiers made for other purposes and pressed into service, but the electric guitar and its amplification quickly developed a life of its own, supported by specialist manufacturers.

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