the Quad II production model. Leak and Walker tried to commercialize their ideas on the meagre post-war British market; their achievements were practically unknown outside of the United Kingdom. Williamson did the opposite: he donated his design to worldwide DIY community, thus securing lasting popular following. In August 1949 Williamson, responding to letters from the readers, published the "New Version" of this amplifier. The article dealt extensively with construction, tuning and troubleshooting issues, however, its main objective was to address stability issues reported in letters from the readers. Apart from the additional frequency compensation network, a biasing potentiometer and a new, indirectly-heated rectifier valve that was not available in 1947, the circuit remained the same. In October 1949 – January 1950 and May 1952 Williamson published a series of articles on matching preamplifier stages and brief "Replies to Queries" concerning assembly and testing. A collection of articles published by Williamson in 1947–1950 was printed as a standalone 36-page brochure in 1952, with a second edition in 1953. The Williamson amplifier itself, as described in the August 1949 issue of Wireless World, remained unchanged. Reception The Williamson amplifier was an instant success. The publication coincided with the resumption of television broadcasting, the beginning of FM broadcasting, the release of the first high fidelity gramophone records (Decca ffrr and the LP record), and the "discovery" of the captured German Magnetophon. The high fidelity media that did not exist in the 1930s became a reality, and the public wanted playback equipment of matching quality. Off-the-shelf amplifiers available in 1947 were not fit for the task. At the same time, electronic components markets were flooded with military surplus, including cheap American 6L6 and 807 power valves. For a while, DIY construction was the only way to obtain high fidelity amplification. Thousands of amateurs began copying the Williamson design; the required transformers and chassis were soon provided by industry. In September 1947 Australians R. H. Astor and Fritz Langford-Smith adapted the Williamson circuit for American 6SN7 and 807 valves; a 6L6 variant followed soon. British and Australian press was unanimously enthusiastic: "by far the best we have ever tested ... extraordinary linearity and lack of harmonic and intermodulation distortion", "amplifier to end [all] amplifiers", "absolute tops for obtaining natural reproduction" and so on. America lagged behind by about two years: first reviews appeared in the second half of 1949, and were just as complimentary. American