An audio amplifier that uses vacuum tubes instead of transistors. Most aficionados of high-quality audio believe that vacuum tubes provide a more musical and more pleasing sound than transistor-based amplifiers. These are subjective opinions that often depend on the hearing ability of the listener. Many people cannot hear much difference between medium-quality and high-quality sound systems. Nevertheless, the most expensive amplifiers are tube based. See audiophile, stereophile, high-resolution audio and vacuum tube.