The thermionic valve, or the vacuum tube, governed the field of audio for over a half century, beginning from the 1920s. Refinements in design led to classic amplifiers such as the Williamson "High Quality Amplifier", and Peter Walker's QUAD Mono Amplifier. Further developments led to Frank McIntosh and Gordon Gow's 50W-1 amplifier, and David Hafler and Herbert Keroes's Acro Ultra-Linear amplifier. This design was adopted by many manufacturers such as Marantz, Harmon-Kardon, Fisher, Scott, and Dynaco in the US. Classic designs were produced from companies in the UK such as QUAD, Leak, and Rogers.

In the 1960s, a little semiconductor device called a transistor took over. Engineers and designers reveled in the idea of replacing the large, fragile glass envelopes of valves with these solid-state devices.

But the death knell of valves was premature. Audio enthusiasts continued working with valves, and in refining designs for music reproduction. In fact, the last 20 years has seen a resurgence and a renaissance in valve audio technology!

In the entertainment industry, involving the human auditory senses, the relentless march of technology has only been questioned by individuals and small groups pursuing a more meaningful experience. In fact, it is they that have ultimately led to genuine advances and an understanding of the human experience. And, it is they that have kept valve technology alive.

Because, valve designs produce a more musically satisfying sound.

In this imperfect world of ours, there are no perfect amplifying devices. The audio signal is a delicate and complex signal, and is affected by all components in its path. Any alteration or addition to this signal is a form of distortion. Once degraded, the signal can never be improved.

Valve circuits are inherently simpler than transistor circuits, and degrade the signal less.

Transistor circuits tend to produce distortion with high-order harmonics. These are dissonant to the ears, and lend an edge and harshness to music. The standard crutch to reduce overall distortion in transistor amps is to add large amounts of global negative feedback. This does reduce overall distortion, but it also adds small amounts of higher-order harmonics. These contribute more towards that harshness in sound.

Valve circuits produce primarily second- and third-order harmonics. Since valve designs are inherently linear, they can avoid the use of global feedback, and stay away from high-order harmonics.

Low-order harmonics are congruent to human hearing, and add a sense of warmth to music.

Valves reproduce the dynamics of music more realistically. They resolve low level information better, as well as the rise and fall of transient signals. All this adds body to the sound of instruments, closer to the complex harmonic structure of real instruments.

Valve amps reproduce the complex harmonic structure of instruments more realistically.

Any doubts as to why valve amps sound better!