LEAK

Typical designs used were similar to those found in the Partridge Public Address Manuals of the time, which used Osram's DA30 power triodes in push-pull for 45 watts output.

During the latter part of the Second World War, the company started developing amplifiers that made extensive use of negative feedback to achieve very high performance.

This approach had been patented by Harold Black of Bell Telephone Laboratories in 1934, and already used before that by Alan Blumlein of EMI, but it was slow to emerge as popular method for controlling amplifier performance.

This first "Point One" amplifier was known as the Type 15, and produced 15 watts output, at 0.1% distortion, using push-pull KT66 valves connected as triodes, with 26 dB feedback applied over four stages.

This amplifier had the same high performance at reduced cost, and it was responsible for establishing and securing the future of the company as a dominant player in the "hi-fi" boom of the 1950s and 1960s.