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|Industry||Electronics, hi-fi equipment|
|Fate||Renamed Sinclair Electronics Ltd. (September 1979)|
|Founded||Cambridge, England (1961)|
|Key people||Sir Clive Sinclair, Founder, Nigel Searle|
|Products||Sinclair Executive, Sinclair Scientific, Black Watch|
|Revenue||£6.3 million GBP (1975)|
After raising funds to start the business by writing articles for Practical Wireless magazine, Clive Sinclair founded Sinclair Radionics Ltd. on 25 July 1961.
Radios and Hi-Fi 
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 Cambridge Consultants. In 1963 Sinclair Radionics introduced their first radio with the "Sinclair Slimline" in kit form at forty-nine shillings and sixpence. A year later in 1964 Sinclair released the "Micro-6", match-box size radio which the company claimed was the "world's smallest radio". It could also be worn on your wrist with the "Transrista". 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 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 It was eventually superseded by the more advanced "Project 80" kit in 1974.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. A class D switching amplifier that was good in theory but sadly ahead of its time and available technology. The amplifier used low frequency germanium transistors as pulse width modulators and switches and wrongly relied on the loudspeaker's inductance to filter the class D signal into audio. Most often this would short out the output transistors. When it did work the power level was far below 10 watts and Sinclair's main advertising channel, Wireless World Magazine, was so deluged with complaints that it supposedly refused to take further advertisements form Sinclair.
Calculators and test equipment 
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 Sinclair Executive, for £79.95. The calculator only included basic maths functions, and the LED display required lots of power. It is often credited as being the world's first attractively-styled calculator that didn't require mains power to be used like prior calculators. The Executive was a phenomenal success, earning Sinclair £1.8m in profit. In 1973 the slightly larger Sinclair Cambridge was introduced at a far cheaper price of £29.95 + VAT. A cheaper Executive was also launched shortly after. In addition to expanding the Cambridge range, the Sinclair Cambridge Scientific was launched in 1975. It was a scientific pocket calculator for the very competitive price of £49.95. In 1977 a revised model, the "Scientific Programmable", was released at £29.95. The Scientific Programmable Mark 2 was later released, reducing the price to £17.22.
In 1975 Sinclair Radionics launched the Oxford range of briefcase calculators. Sinclair also attempted to capture the top-end calculator market with the Sinclair Sovereign, available in plated gold or silver. The calculator was critically acclaimed for its excellent engineering and design and enjoyed short success. A final attempts at the mass-market for calculators, the Sinclair Enterprise and the President did not sell well.
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.
Black Watch 
In August 1975 Sinclair introduced the Black Watch digital watch at £17.95 in kit form and £24.95 ready-built, although this wasn't available to buy until January 1976. Including a five-digit LED display, it suffered from technical flaws related with the design of the case, the chip, the battery and accuracy. Not only was the watch unreliable, Radionics was not able to fulfil the orders it had taken. As a result, Radionics made its first loss in the financial year April 1974-April 1975. The Black Watch fiasco had a devastating effect on Sinclair's finances and the company would have gone bankrupt had not the Government, through the National Enterprise Board, stepped in to support it.
Portable televisions 
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 National Enterprise Board bought a 43% stake in Sinclair Radionics for £650,000, and in October the National Research and Development Council agreed to provide £1m for a revived portable TV project, which was finally launched in January 1977 as the Microvision TV1A and MON1A at £99.95. Supply exceeded demand, and 12,000 units were left unsold until they were sold off cheaply. This resulted in a £480,000 loss for Sinclair. Sir Clive Sinclair was certain that the TV1B model released in 1978 would be more successful, but sales were disappointing.
In May 1979 the NEB announced that it intended to sell Radionics' calculator and TV interests; they were bought by the ESL Bristol group (as Radionic Products Ltd.) and Binatone respectively. In July Clive Sinclair resigned with a £10,000 golden handshake. In September the NEB renamed what was left of Radionics (i.e. the scientific instrument business) as Sinclair Electronics Ltd.; in January 1980 this was changed to Thandar Electronics Ltd. As of 2008 this business continues, now called Thurlby Thandar Instruments.
Sinclair Instrument and Science of Cambridge 
When it became clear that Radionics was failing, Clive Sinclair took steps to ensure that he would be able to continue to pursue his commercial goals: in February 1975, he changed the name of Ablesdeal Ltd. (an off-the-shelf company he bought in September 1973 for just such an eventuality) to Westminster Mail Order Ltd.; this was changed to Sinclair Instrument Ltd. in August 1975.
Finding it inconvenient to share control after the NEB became involved in Radionics, Sinclair encouraged Chris Curry, who had been working for Radionics since 1966, to leave and get Sinclair Instrument up and running.
Sinclair Instrument developed the "Wrist Calculator" to generate cash, which soon became a commercial success selling in surprising figures. In July 1977 Sinclair Instrument Ltd was renamed to Science of Cambridge Ltd. Around about the same time Ian Williamson showed Chris Curry a prototype microcomputer based around a National Semiconductor SC/MP microprocessor and some parts taken from an earlier Sinclair calculator. This was sold as the MK14 microcomputer kit. Science of Cambridge ultimately became Sinclair Research Ltd.
- Scott, David (November 1974). "Peanut hi-fi". Popular Science 205 (5): p. 44. ISSN 0161-7370.
- "What does it take to build the world's smallest scientific calculator?". Popular Mechanics 143 (1): p. 5. January 1975. ISSN 0032-4558.
- Arnold, William (January 9, 1975). "Sinclair keep it lean". Electronics (New York: McGraw Hill) 48 (1): pp. 76–77. "...introduced a 3 1/2 digit multimeter based on a LSI chip and continues to make audio equipment". "Sinclair Radionics has only 250 employee and expects to make about $17 million for its fiscal year ending in March ".
- Owen, Chris (1985-11-13). "Multimeters". Planet Sinclair. Retrieved 19 October 2009.
- Sinclair Radionics (December 1975). "The Black Watch Kit". Popular Mechanics 144 (6): p. 125. ISSN 0032-4558.
- Owen, Chris. "The Black Watch". Planet Sinclair. Retrieved 19 October 2009.
- Thurlby Thandar Instruments Limited (successor to Thandar Electronics Ltd)