A tube amplifier, or tube amp as they are commonly called, is an amplifier that receives power from vacuum tubes. The tubes are famous for producing not only significant power, but a smooth sound as compared to an all-electronic or transistor amplifier. Brought to the forefront in the 1960s, the tube amplifier was responsible for the easily recognizable guitar licks of some of the most famous guitarists of modern rock-'n'-roll music. A trademark of the tube amplifier is that the amplifier produces the best sound when played at its loudest setting. This also results in an enormous amount of electrical feedback, known as distortion, that created what has been referred to as the sound of the 1960s by many music aficionados.
The vacuum valve or power valve is the heart of the tube amplifier. Originally designed to work with telephones, radar and various military applications, the vacuum valve soon found its way into musical amplification devices. Microphone pre-amps and guitar amplifiers found the vacuum valve very conducive to warm tones and powerful sound. The negative feedback, or simply feedback as the musicians referred to it, was soon modeled into a type of musical note all its own. Some of the first guitarists to successfully transform the eerie sound into working notes were renowned for their genius in doing so. In the 1960s, the tube amplifier reigned supreme with most professional guitarists.
In the mid 1970s, the solid state electronic amplifiers began to emerge as a less-expensive and more durable option in amplification. The tubes were not only costly, they were prone to breakage or burnout, requiring spare tubes to be carried to most shows. The solid state amplifiers claimed to produce a tube amplifier sound, however, many musicians disagreed. While close, the solid state amps did not produce the tonal qualities of the tube amplifier and the majority of professional musicians began to once again use tube amps on the road and in the studio.
The decline in power tube production since the 1980s has made the cost of a tube amp a sizable investment for many guitarists and the tubes are now used mainly in high-power transmitters, microwave ovens and guitar amplifiers. The telltale hum and the soft, red glow of the power tubes makes the tube amplifier a visual centerpiece of a band stand as the amp sits in wait for the band to begin playing. In an effort to create the sound a tube amp makes when at full volume, yet eliminate some of the noise, some manufacturers have created a device that will actually absorb some of the amp's power while still allowing the sound to emanate from the speakers.