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Sinclair Cambridge models

The Sinclair Cambridge was introduced in summer 1973, and was the first of a range of a dozen models and variations.  Some of the models were available as ready-made units or as self-assembly kits.

This page illustrates the several varieties of the basic Sinclair Cambridge calculator, which can be distinguished by the key arrangements.
Here are what we believe to be all of the models in what we think is their chronological order.

Sinclair Cambridge type 1

Sinclair Cambridge type 1
Inside Sinclair Cambridge type 1
Inside a modified Sinclair Cambridge type 1

Sinclair Cambridge (type 1).

8 digits, red LED.

4-functions, constant.

Has [C] and [K] (constant) keys.

Batteries: 4x AAA.

Main integrated circuit - General Instruments Microelectronics GI-C550, here date coded mid-1973.

50 mm x 111 mm x 28 mm (2" x 4.4" x 1.1").

Made in England.

The first of the very small Sinclair Cambridge series, introduced in Summer 1973
In Britain in September 1973 it cost GBP £43.95 fully assembled and GBP £ £29.95 as build-it-yourself kit[1].
In the U.S.A. in January 1974 it cost US$99.95 fully assembled and US$79.95 as a build-it-yourself kit[2].

The case has a glossy finish, with a poorer quality moulding than usual for Sinclair. The main chip is in a more expensive ceramic package.

Catherine Palmer has kindly supplied the photograph above of the circuit board of a Sinclair Cambridge type 1 with a factory modification.  This has a second display driver integrated circuit from ITT (International Telephone & Telegraph) which has been laboriously soldered with flying leads to replace 8 diodes around the Bowmar display.  This may have been found necessary in order to produce a reliable display after the calculator went to market. 

Sinclair Cambridge type 2

Sinclair Cambridge type 2
Inside Sinclair Cambridge type 2

Sinclair Cambridge (type 2).

8 digits, red LED.

4-functions.
Has no K (constant) key, but has automatic constant on all functions i.e. the second operand of all calculations is automaically stored as the constant factor.
Has [C] and [CE] (clear last entry) keys.

Batteries: 4x AAA.

Main integrated circuit - Texas Instruments TMS0801NC, here date coded end of 1973.

50 mm x 111 mm x 28 mm (2" x 4.4" x 1.1").

Made in England.

Sinclair Cambridge type 3

Sinclair Cambridge type 3
Inside Sinclair Cambridge type 3

Sinclair Cambridge (type 3).

8 digits, red LED.

4-functions, constant.
Has [C/CE] (one press clears last entry and two presses clears everything) and [K] (constant) keys.

6v (4 x AAA).

Main integrated circuit - General Instruments Microelectronics GIMT-CZ550,here date coded to the end of 1975.

50 mm x 111 mm x 28 mm (2" x 4.4" x 1.1").

Made in England.

This Cambridge model is a later, more common, version of the Cambridge.
It was also available as a self-build kit, as pictured below.

Sinclair Cambridge type 3, version Manufactured in Spain

Sinclair Cambridge made in Spain

Javier Ortiz has kindly provided this photograph of the back of a Sinclair Cambridge type 3 manufactured under licence in Spain.

It says "FABRICADO EN ESPANA
Bajo licencia sinclair"

Translated "Made in Spain
Under licence sinclair"

Sinclair Cambridge type 3, self-build kit

Sinclair CambridgeKit

A Sinclair Cambridge calculator kit, still shrink-wrapped in the polystyrene container.

Sinclair Cambridge Kit
Sinclair Cambridge Kit

The assembly instructions for the Sinclair Cambridge calculator kit.

The components of the Sinclair Cambridge calculator kit, there is also a bag of small parts out of view.

Sinclair Cambridge type 4, Sinclair Cambridge %

Sinclair Cambridge type 4
Inside Sinclair Cambridge type 4

Sinclair Cambridge (type 4) & Sinclair Cambridge %

8 digits, red LED.

4-functions, %.
Has [C], [CE] (clear last entry), and [%] keys.

Batteries: This model takes only 2x AAA.

Main integrated circuit - In the Sinclair Cambridge type 4 above, General Instruments G-595, here date coded to the end of 1975.

50 mm x 111 mm x 28 mm (2" x 4.4" x 1.1").

Made in England.

The Sinclair Cambridge %, below, may be identical to the Sinclair Cambridge (type 4) apart from the label on the front.

Sinclair Cambridge %

The model above is labelled 'Sinclair Cambridge %' and appears to be identical to the 'Sinclair Cambridge' type 4.  The '%' may have been added to emphasise that the Cambridge now has the % function.  Photograph kindly supplied by Pino Lombardi.

Note the use of LED displays manufactured by Bowmar, the pioneering U.S. calculator manufacturer, in these models.

Price plummets:
When first introduced in summer 1973 the Cambridge cost £43.95 Sterling [about US$100].
In Summer 1977 the mail-order discount price had dropped to £8.95 Sterling [about $US15], one fifth of the original price.

 

 

References:

  1. Everyday Electronics, September 1973, p460.
  2. "Skinny mini", Popular Science, January 1974, p69

Vintage British Calculators

Text & photographs copyright, except where stated otherwise, © Nigel Tout 2000-2024.