Following the lead of several other manufacturers who had begun to produce transistor amplifiers in the early sixties, Quad produced their first solid state amplifier in 1966, the mono series 50, which was intended primarily for studio and professional use. Shortly after, in 1967 Quad brought out their domestic version, the 303 stereo power amplifier (named 303 as it produced 30 volts peak at 3A output), identical in appearance to the 50 and 50/E and accompanied by the 33 control unit which was the successor to the valve 22 control unit and also totally solid state.

The 303 was a very stable and robust design and was used by several recording studios and rock groups ( Pink Floyd, for one). It was perfect for driving the Quad Electrostatic speakers (ESL 57's) but in some opinions, a little 'woolly' when connected to conventional loudspeakers. (I had one of these set-ups for several years in the mid 1970s driving a pair of B&W Studio monitors - 'Dark Side of The Moon' sounded terrific!)

The outstanding performance of the Quad 303 was largely due to a unique circuit developed by Quad. The 'Triples' output circuit of the 303 for the first time successfully overcame the problems of thermal tracking in Class B amplifiers. This was an original development carried out by the company and was the subject of articles in Wireless World and similar technical journals overseas. The circuit employed symmetrical 'triples' which greatly reduced distortion (0.1 per cent distortion for 45 watts output at 10,000 Hz ) and rendered the quiescent current independent of output transistor temperature. The use of triples permitted simple and effective control of the output current and, since the voltage was also controlled, the output transistors were completely protected, always operating within their ratings. The benefits of this were obviously improved reliability under all conditions without the use of elaborate and expensive protection circuitry.

The 303 earned Quad a Council of Industrial Design Award in 1969.

Originally priced at £98 for the pair (power amplifier and control unit), today expect to pay between £175 and £300 for a good, clean working 303/33 set; and up to £400 with matching tuner (pictured lower right).

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