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|Fate||Renamed Sinclair Electronics Ltd. (September 1979)|
After raising funds to start the business by writing articles for Practical Wireless magazine, and borrowing £50,  Clive Sinclair founded Sinclair Radionics Ltd. on 25 July 1961. Sinclair initially worked alone in the evenings out of a room in London (he was still a technical journalist during the day), selling radio kits by mail order.
Radionics initially developed hi-fi equipment; it released its first product, the Sinclair Micro-amplifier, in December 1962. The assembly and distribution of this product were contracted out to
A year later, in 1964, Sinclair released the "X-10" amplifier, one of the first commercial
In 1965 the "Micro-FM" debuted as "the world"s first pocket-size FM tuner-receiver", but was unsuccessful due to technical difficulties. Despite problems, illegal clones were produced in the far-east. Sinclair's final 1960s radio kit was the 1967 "Micromatic", billed as "the world's smallest radio" like Sinclair's earlier radios. The "Micromatic" was a reasonable success and was sold until 1971. In May 1971 Sinclair Radionics made £85,000 profit on £563,000 turnover; the following year profit increased to £97,000 on turnover of £761,000.
In 1966, Sinclair Radionics re-entered the hi-fi market with the "Stereo 25", a low-cost pre-amp control system. Production was halted in 1968 due to low supply of transistors which had been purchased in 1964 as rejects from other manufacturers. In 1969 it was replaced by the "Stereo Sixty". This soon became Sinclair's most successful audio product, being the second product of the "Project 60" range. The "Project 60" products sold well and were supplemented by the "Project 605" kit in 1972. It was eventually superseded by the more advanced "Project 80" kit in 1974.  In May 1973 Sinclair Radionics generated £1.8m turnover. The last Sinclair Radionics hi-fi product was the System 4000, in 1974.
Another Sinclair Radionics product that was introduced in 1964 and failed was the first class D amplifier kit rated at 10 watt RMS.[
Sinclair Radionics launched the System 2000 amplifer, FM tuner and loudspeaker in 1968. followed by the System 3000 in 1972.
In 1972, Radionics launched its first electronic calculator, the Executive, which was considerably smaller than its competitors since it had been possible to use hearing-aid-sized batteries. It had been discovered that there was considerable latency in the display and memory and that, with the addition of a timer, power could be withheld from these battery-draining components for much of the time.
During the majority of the 1970s, Sinclair focused on building the most affordable pocket calculators with the best design. In 1972 Sinclair released the world's first slim-line pocket calculator, the
In 1975, Sinclair Radionics launched the
In 1974, Radionics launched the DM1 digital multimeter.  Such scientific instruments were to form a quiet backbone of Radionics business for the rest of its existence. In marked contrast to the rest of the Sinclair range, the instruments gained a reputation for reliable conventionality rather than often unreliable idiosyncrasy. 
In August 1975, Sinclair introduced the
In 1966, Sinclair Radionics developed the world's first portable television, the "Microvision", but never attempted to sell it because development costs would have been too high based on the complicated design the Microvision used.
In April 1976, the