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Sinclair Radionics PZ2 and PZ3 power supply

In 1965 Sinclair Radionics released their first mains power supply, to power the Sinclair Z12 amplifier. There is very little on the www about the PZ2 but it consisted of a transformer mounted on an L-shaped aluminium chassis with a rectifier and a smoothing capacitor. This arrangement was barely adequate because of the mains hum from the poor smoothing.

So later thay year (1965) the PZ3 was introduced. On the upright part of the chassis was mounted a power transistor, with other components mounted on its legs. There was a tag strip for the output. The circuit had two smoothing capacitors.

The circuit is unusual as it was not stabilised but used a gyrator as a smoothing element. A gyrator is an electronic inductor - the circuit is described on 4QDTEC, where it is used as a tuned circuit. This resulted in a very smooth output that is ripple-free, so no mains hum, but not stabilised.


Unfortunately Clive specified 1/16 inch (1.6mm) thick aluminium for the chassis. This was not thick enough to support the heavy transformer so many of these units got badly bent in post.

The PZ3 (if I recall correctly) had no circuit board and two large capacitors, so it was not very cheap to produce. It was soon replaced by the PZ4 which, although mounted on a similar chassis, had only one reservoir capacitor but was stabilized. The components were mounted on a PCB which made production easier and removing one larger expensive reservoir capacitor made production more economical.

The gyrator was a "clever" idea introduced by Martin Wilcox who had joined Sinclair Radionics in February 1965. However Clive Sinclair wrote a letter about the gyrator principle which was published in Wireless World, March 1967 [page 40 (140)]. You can get a pdf of this Wireless World, March 1967 from American Radio History. Page 47 (147) also announces Sinclair's Z120.

As there is so little information on the PZ2 and PZ3 I would appreciate contact with anyone who actually has one!

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First published: Tuesday the 27th of February, 2018
Last modified: Thu, 08 Dec 2022 10:40:11 GMT
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