Desk Electronic Calculators

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Physics Department, Kings College,
Durham University, Calculator

The British journal "Wireless World" in a report in 1962 on new developments in electronics shown at the Physical Society Exhibition, Jan 15 - 19, 1962, in London, reported an electronic desktop calculator. It was a hybrid using Dekatrons, trigger-tubes, and transistors[1]:

"Desk calculator shown by the Physics Department of Kings College, Durham University, used relatively simple circuits built around p-n-p and n-p-n transistors, bi-directional Dekatron counters and cold-cathode trigger tubes.   A feature of this device is that only very few switches are needed, since the trigger tubes (which set up numbers and instructions into the Dekatron accumulator) are activated simply by touching a finger across two electrodes so as to bleed in a small extra current (200μA) to the tube (they are already biased nearly on)."


In May 1962 the journal "Electronic Engineering" carried an article titled "An Electronic Desk Calculating Machine", by L. Molyneux, B.Sc, Ph.D., of King's College, Durham University, which gives much more technical information about this calculator[2].

Molyneux explained his thinking behind the design of the calculator:
    "Although there is, at the present time, enormous activity in the design and production of electronic computers, little or no interest is being shown in an electronic counterpart of the mechanical desk calculating machine.
    Since such a device is clearly technically possible, it may well be that the lack of interest is due to the supposition that an electronic version would be very complex and costly compared with mechanical machines.  However, several new factors, when taken together, suggested that it might be possible to make a competitive electronic machine, and a design has been worked out and tested in abbreviated form.  The new factors are as follows.  Firstly npn transistors (which may be driven directly from decade counting tubes) are now available at a reasonable price (e.g. Texas Instruments type 2S701), secondly a new Dekatron (GS10G Ericsson Ltd) counting tube has been developed which has special connexions that allow simple interstage coupling for bi-directional counting over many decades. ... Thirdly a simple trigger tube (Ericsson type GTR120W) is available at a very low price."

The calculator described is very primitive, having just two working decades and without a proper numeric display, so is a "proof-of-concept" rather than being a prototype.  For instance, the arrangement of the "keyboard" is explained further:
    "Each decade of the keyboard requires 20 trigger tubes.  Ten of these are called control tubes and are set by 'touch' contacts on the keyboard surface.  Each of the other tubes is biased by one of the control tubes.
    The trigger electrode requires only a few micro-amperes to ionize the gas of the main anode circuit and this current may be provided by bridging two contacts with a finger tip.  Provided the current flowing through the finger tip is less than (250μA) nothing is felt by the operator.
[Emphasis added]  A number is therefore set in the keyboard by touching the contacts of the digits required in each decade. ... When ionised the tubes give a blue glow which can be used to indicate the number chosen. ...
    "The accumulator requires one Dekatron for each decade. ... At present the number is indicated by the position of the cathode glow but later a new type of Dekatron is promised ... which will drive a numerical indicating tube directly."

So, it appears that this was a four-function "full-keyboard" machine but was a very primitive proof-of-concept, using just pairs of electrical "touch" contacts in each decade column and without a numerical display.  Molyneux would not have been aware that the ANITA Mk VII and Mk 8 electronic desktop calculators were actually being developed and were launched at just this time.



  1. "Physical Society Exhibition: New Developments in Electronics: Computing", Wireless World, March 1962, p120.
  2. Molyneux, L., "An Electronic Desk Calculating Machine", Electronic Engineering, May 1962, pp294-299.

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