Retro: Sinclair Cambridge Type 3 Calculator


It’s taken me quite a long time to get my hands on my first Cambridge.  The ever-genial Dave from Retonthenet has known for a little while that I collect vintage tech, and approached me via Twitter saying that there was one for sale.  The price was absolutely right and was in my possession in a very short space of time (the packaging was superb and would have easily protected a much-less-fragile item than this).

The Cambridge was introduced by Sinclair Radionics in August 1973.  In those days you could probably buy it from Boots, Lasky’s and Timothy Whites, as well as directly from Sinclair in Cambridge.  It came as a kit or pre-assembled.  There were seven models in the range: there was the original four-function Cambridge, Cambridge Scientific, Cambridge Memory, two Cambridge Memory %’s, Cambridge Scientific Programmable and Cambridge Universal.


The Cambridge followed on from the Executive, Sinclair’s very first calculator in 1972.  a major factor in the success of the Cambridge was its low price – £32.95 assembled or £27.45 as a kit (which was basically a case and a plastic bag full of resistors).  It was still doing the rounds by the Summer of 1977, where the price had literally crashed to £8.95, a fifth of its original price.  The manual that came with it was quite extensive.  It weighs less than 3.5 ounces and measured 50 x 111 x 8mm.  It ran on 4 AAA batteries.  It was built using the cheapest components available to man, which a) kept the cost down and b) led to some real common failures.  The switch contacts often failed, meaning you couldn’t turn the device off. The switch contacts were made of nickel coated in tin rather than gold, so an oxide layer would build up across the insulating barrier when the switch was repeatedly used.


The display was an eight-digit LED made by National Semiconductor with a five-digit mantissa and two-digit exponent.  Later models required such a huge power draw that the four AAA’s were replaced by a 9v PP3, meaning the battery compartment was a lot bigger and required a different battery cover.




Battery compartment label says you should use Ever Ready or BEREC batteries.  I always thought BEREC stood for ‘British Ever Ready Electrical Company’, so isn’t that the same thing?  Note the Sinclair branded motherboard.  Date code is probably obscured by the label.  ‘Popular Science’ magazine, on page 69 of its January 1974 issue, branded the Cambridge the ‘Skinny Mini’.

My sincere thanks again to Dave and the chaps at Retonthenet – rest-assured I’ll be badgering them often to see what other beauties they have for sale.  Meantime, I implore you to take a look at their great website, and hopefully you’ll be able to get your hands on some bargains, too.  And tell them Steve sent you …