Quad 33/303 (1967)
Two boxes, no meters, no wood grain - just the first all-transistor Quad, and a power amp whose output circuit was important enough that the technical journals wrote it up.
Overview
In 1967, according to Quad's own company history, the Acoustical Manufacturing Co. introduced the first all-transistorised Quad 33-303 units, the control unit and the power amplifier. They remained current models for years afterward. Quad didn't chase the transistor revolution with a flashy new look. The 33/303 kept the house aesthetic and put the change inside the box.
The 303's output stage is the part collectors and engineers actually talk about. Quad's history describes it as a "Triples" output circuit, developed in-house to overcome the thermal-tracking problems that dogged Class B amplifiers of the period. It was the subject of articles in Wireless World and similar technical journals overseas, alongside write-ups of other original Quad features like the cathode-coupled output transformer and the two-lamp tuning indicator for the VHF/FM tuner.
The 33 control unit is the other half of the pair, and the service documentation treats them as a system. The Quad 33-303 service supplement gives separate circuit descriptions for each, plus sections on dismantling the pushbuttons, setting up the 303, fault location, a summary of pushbutton switching, modifications, and component lists. It's a repair-oriented document. These units were expected to live on a bench, opened up, and kept running.
The period literature makes clear what the 33/303 was meant to sit alongside. Quad's advertising in the audio press presented the 33/303 amplifiers together with the FM3 stereo and AM3 tuners and the electrostatic loudspeakers, promoting them as the closest approach to the original sound (Audio-Collection, 1968, p.122). The Quad 33/303 advertisement from that period lists the 33/303 amplifiers alongside the FM3 stereo and AM3 tuners and the electrostatic loudspeakers (Audio-Collection, 1968, p.122). The FM3 tuner manual describes it as a self-powered tuner designed for use with the Quad 33/303 amplifier. The same goes for the AM3, which Quad intended primarily for the 33/303 but noted could be used with other amplifiers if required.
Quad's own history has a detail about the professional market. Roughly ten percent of the company's output went to professional rather than domestic users, and broadcast and recording studios in many countries regarded the same equipment sold to private customers as being of professional quality. The 33/303 was part of that. The same history notes that the Design Council exhibited Quad products frequently and presented Design Council Awards for the Quad 33-303 and the Quad 405. So the plain, functional face of the 33/303 was recognized design.
Owners who've kept these running describe the 33/303 as very musical, delivering a lot of room information. The service supplement, with its fault-location and modification sections, suggests Quad expected these to be maintained rather than replaced.
The 33/303 sits in a specific place in Quad's timeline. The stereo version of the Quad control unit, the Quad 22, appeared in 1959, and the multiplex decoder for stereo broadcasts in 1964. Then 1967 brought the all-transistor 33/303. The company's history notes that exports formed a significant proportion of turnover, about sixty-five percent of production sold in 65 countries, with major markets in Europe, Canada, the USA and Japan. A lot of 33/303 units went abroad, which is part of why they still turn up on the secondhand market in so many countries.
One thing for anyone shopping: the 33/303 is a two-box system, and the tuners that pair with it (FM3, AM3) are separate self-powered units. Buying a "33/303" that turns out to be just the control unit, or just the power amp, is a common confusion. The service supplement covers both, and the two were sold and used together.
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Related Models
- Quad 50E (1966–1983)
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