List of valve amplifier designs

The first commercially produced amplifier with distortion of 0.1% was the LEAK Type 15 "Point One" of 1945, using KT66 vacuum tubes (valves) connected as triodes, with 26 dB feedback over 4 stages including the output transformer.

In 1948 LEAK produced the TL/12 which was also rated at 0.1% but featured improved performance with 26 dB over 3 stages and the output transformer (giving better gain-margin and phase-margin).

The TL/12 sold in large quantities to professional users, radio stations, laboratories, as well as to the emerging market for hi-fi equipment.

The design featured 5 tubes with 10 watts output: EF86 as preamplifier, ECC83 phase-splitting, two EL84 in push-pull configuration, EZ80 rectifier.

Dynaco was a major US manufacturer of completed and kit amplifiers of high quality, notably of the Mark III and the Stereo 70, claimed to be the most popular tube amp ever made with over 300,000 produced.