built by Western Electric around their 300A and 300B power triodes, far exceeded the average level but were expensive and rare. By the middle of the 1930s Western Electric and RCA improved performance of their experimental audio equipment to a level approaching modern understanding of high fidelity, but none of these systems could be commercialized yet. They lacked sound sources of matching quality. Industry leaders of the 1930s agreed that the improvement of commercial amplifiers and loudspeakers would make sense only after the introduction of new physical media surpassing low-quality AM broadcasting and shellac records. The Great Depression, World War II and the post-war television boomconsecutively delayed this goal. Development of commercial audio equipment came to a standstill; the few enthusiasts seeking higher level of fidelity had to literally do it themselves. American DIYers experimented with novel beam tetrodes. Australians preferred traditional push-pull circuits built around directly-heated triodes and complex, expensive interstage transformers. British school of thought led by Walter Cocking of Wireless World leaned to push-pull, class A, RC-coupled triode output stages. RC coupling, as opposed to transformer coupling, argued Cocking, extended the amplifier's bandwidth beyond the required minimum of 10 kHz and improved its transient response. Tetrodes and pentodes were undesirable due to higher harmonic distortion and higher output impedance that failed to control fundamental resonance of the loudspeaker. Cocking wrote that Kellogg's 5% distortion limit was too high for quality amplification, and outlined a different set of requirements - the first definition of high fidelity. Instead of Kellogg's single figure of merit (harmonic distortion), Cocking set three simultaneous targets - low frequency distortion, low harmonic distortion, and low phase distortion. In 1934 Cocking published his first Quality Amplifier design - a two-stage, RC-coupled triode class A amplifier that achieved no more than 2–3% maximum distortion without using feedback. Feedback appeared in his 1943 Wartime Quality Amplifier, built around American 6V6 beam tetrodes; however, both the input stage and the output transformer were placed outside the feedback loop. Cocking's Quality Amplifier family became the foundation of post-war British and Australian audio industry, including the Williamson amplifier. Development In 1943, in the middle of World War II, twenty-year-old Scotsman Theo Williamson failed mathematics exam and was discharged from the University of Edinburgh. Theo was not physically fit for military service, so instead the authorities drafted him for mandatory civilian work at Marconi-Osram Valve. In April 1944 Williamson transferred from