The introduction of the Williamson Amplifier in the late 1940s changed the hi-fi world forever. Throughout the 1930s, technicians and inventors had made great progress in developing technologies that resulted in improvements in the sound quality of music and sound systems. For instance, microphones introduced in the 1940s were made to deliver the full range of audible frequencies with low distortion. FM radio, introduced in the late 1930s, provided listeners with a new source of music and entertainment with excellent fidelity. There were changes in sound technology that were transformed from expensive, commercial systems, such as those used in the movie industry, to inexpensive consumer items. One of these was the famous Williamson Amplifier circuit.
D. T. N. Williamson was an English engineer working for the M. O. Valve Company. He later worked for the Ferranti Company. His amplifier circuit design was first published in a series of articles in the magazine Wireless World in 1947, and it immediately attracted a lot of attention. The design was not very complex, but it was carefully worked out to maximize the performance of the tubes and other components involved. Williamson recommended the use of a type of tube called the KT66 that remains in use today. Part of what gave his amplifier such good sound was the use of a very expensive, custom-made output transformer. Transformers are used in the electric power system to convert high voltage to low voltage or vice versa, but in an audio amplifier, transformers are used to make the output of vacuum tubes suitable for use in operating loudspeakers. They are a crucial stage between the electronics and the ears, and so they must be very carefully designed and constructed.
There have been many high fidelity amplifier designs since that time, but the Williamson circuit has remained popular. Interestingly, Williamson himself never formed a company to make amplifiers, but instead offered his design to others for free. Many companies offered products using his circuit, and many hobbyists built their own Williamsons over the years.