Gear & technology
Tube amplifier
Also called valve amplifier, tube amp, valve amp
A tube amplifier uses vacuum tubes, also called valves, instead of transistors to amplify the signal. Tube amps measure worse than solid-state designs but are loved for a sound many describe as warm and full, and for the glow.
Tubes were the only way to amplify before transistors arrived in the 1950s, and they survive in audio because of how they distort: mostly low-order harmonics that many listeners find agreeable, and a gentle overload instead of a hard clip. THD figures of 1 percent or more are common and, to tube fans, beside the point.
Tube designs also tend to have a higher Output impedance, which changes the Frequency response of low-impedance headphones, and lower Damping factor for speakers. Part of what people hear as "tube sound" is these interactions rather than the tubes themselves. Hybrid amps use a tube input stage with a Solid-state output to get some of the flavor with more power.
Tubes wear out and need replacing every few thousand hours, run hot and cost more per watt. Objectivists regard the sound as pleasant distortion; owners regard it as the point. Both are describing the same measurements.