Hybrid audio amplifier

Almost fifty years ago, Wireless World (now Electronics World) published the design of an audio output amplifier that gave a new dimension to hl-flt: In the 1930s, Cossor Radio of London had introduced negative feedback (NFB)to improve the distortion characteristics of audio output amplifiers, After the Second World War, the beam tetrode, largely the work of the Marconi-Osram Valve Company of Wembley, London, offered a considerable improvement in distortion (without NFB) over the pentode while retaining the greater efficiency of this valve over that of the output triode, D. Williamson, an engineer working with Marconi-Osram, found that this advantage in efficiency was retained when the screen grid was connected to the anode to form a quasi-triode valve.