The Autodial No. 401, sales name Single Number Callmaker, was made by GEC and field trailed in late 1976/early 1977.

The Callmaker was eventually marketed late 1979 as the Mono Callmaker.

The Single Number Callmaker is contained in an off-white case measuring approximately 250 mm/150 mm, with a hinged lid on covering the lower half.  The units are line powered and have been designed to be wall mounted.

The programming and operating instructions are printed on the inside of the lid.  The Callmaker is capable of storing 11 digits including PABX access digits and has a fixed two second interdigit pause.  Programming is achieved by a matrix of vertical slide switches.  To make a call to the stored number, the user lifts the handset to obtain dial tone and then presses a button on the associated telephone.  This restricted the associated telephone to a Telephone No. 746 or similar, where a push button could be wired to the Callmaker.  Use of the telephone dial may be restricted or may remain available for calls to numbers other than that in the Callmaker storage if required.

On marketed models the lid could be padlocked to a hasp.  Earlier models could be retrofitted using a Lock Bar No 2.

Areas of use envisaged included Automobile Association boxes, local authorities. health centres and airports, docks or main line stations where the public may require direct access to car hire, or hotel facilities.

The Single Number Callmaker replaced the Sender No. 1 , which was used as a dialling aid for the handicapped.  When used for this purpose access will be restricted to the public exchange operator.

Early models were titled Single Number Callmaker.

GEC developed and produced this Autodial.

Taken from New Product Bulletin 3/76

Descriptive Leaflet

3 Internal
Issue 1, June 1979

AUTODIAL No. 401A (Mono Callmaker)

The Autodial No. 401A is capable of sending a predetermined telephone number using loop disconnect pulses of up to 11 digits. The autodial is designed to operate on 45-50v systems, is insensitive to line polarity and is provided with voltage protection.

The Autodial No. 401A measures 250mm long, 150mm wide, and 48mm deep, and weighs 900grams.

It has the facilities for storing and sending a single telephone number of up to eleven digits including PABX access digits. Digit storage is set up by slide controls which operate a switch matrix. The autodial can be used with a normal or loudspeaking telephone and in all cases a press switch will be needed to activate the autodial. The switch is normally fitted in the telephone.

When connected to a PABX extension the access digit(s) is stored before the main exchange number. To allow for correct seizure of the exchange equipment, facilities are provided (by the use of pause slide controls) to increase the inter-digit pause that follows the pulsing of the access digit(s). The interdigital pause is normally 2 seconds, but by changing an internal strap it can be increased to 5 seconds.

In the idle state the autodial is short circuited by a contact of the call switch which allows for incoming calls to be received, and if required, outgoing calls to be made without the autodial.

To make a call using the autodial, to a number which has been previously programmed with the slide controls, the telephone handset is lifted, and when dial tone is received the call switch is operated, the programmed number is then automatically sent at 10 pps.

If the autodial is used on a PABX extension the PAUSE slide control(s) inserts an interdigital pause of 2 seconds. If due to congestion or circuit design, the receipt of dial tone from the main exchange is delayed a strap in the dialler can be moved which will increase the interdigit pause to 5 seconds.

The autodial can be connected to most telephones with exchange access but as it is activated by a button on the telephone instrument there are a few situations where it cannot be fitted as a standard item. Such installations are:-

  • Any combination of plan arrangements where 4 buttons are used.
  • A plan 2A fitted to capacity.
  • HES4.
  • Trimphone where the piano type key is already in use.

The autodial will not operate with any apparatus using multi-frequency or direct current signalling e.g. MF or DC Keyphones.


The following items should be requisitioned:-

  • Autodial No. 401A.
  • Block Terminal No. 35.
  • Switch No. 5A-4.
  • Cable Dist 3595A/4W.

The autodial has been designed for wall mounting, made possible by three holes in the baseplate and is connected to a block terminal by a 4-wire cable (Diagram N2315 refers). The autodial should be fixed at a height which will. allow easy access for programming. Only in exceptional circumstances should the auto-dial be fixed in a horizontal position or provided as a free standing item. Connection to the block terminal in these circumstances should be made using a 4 way cord (CORD INST 4/121AT) where possible.

Access to Terminals and Fixing Holes
Removal of the single fixing screw below the slider controls allows the casing to be removed from the baseplate after disengagement from the two lugs at the opposite end of the autodial. The cover over the electronic circuitry should not be removed as its purpose is to protect the circuit components during installation. Do NOT support the autodial by this cover when fixing the baseplate to a wall because the cover is only a push on fit.

The method of connection is shown in Diagram N2315.

Long Interdigit Pause
After Access Code In normal use, with the strap in the A-B position, the PAUSE slide control(s) inserts an interdigit pause of 2 seconds. If due to congestion etc at the exchange the receipt of dial tone is delayed the strap should be moved to the B-C position, which will effectively increase the interdigit pause to 5 seconds.

Should the autodial need to be locked there is available for early models a clasp which is fitted underneath the base of the dialler and held in place by the lower baseplate fixing screw. The clasp can then be clipped over the lid of the autodial and a small padlock, supplied by the customer, used to lock the lid in a closed position.

On later models a bracket is supplied with the autodial and when the case is removed the bracket will be found temporarily fixed by tape to the top right hand corner of the autodial. This bracket is fitted under the single screw that fixes the case to the baseplate. The knockout in the lid will then have to be removed so that when the lid is closed the bracket protrudes through the lid and a padlock can then be inserted through the hold in the bracket.

The autodial should be installed in accordance with Diagram N 2315. For installations that specifically ask for the removal of the dial, then a Dials Dummy No. 7 should be fitted if the telephones are No. 706, 711, 740, 741 and 746, add a Dials Dummy No. 6A for a Telephone No. 710. Limited access to the public telephone network (999 calls only) can be obtained by fitting a Dial Auto No. 28 FA CLEAR to either a Telephone No. 706 or a Telephone No. 746 .


General Requirements Programme the customer's required number and check for correct access.

For test purposes it is also necessary to check that all slide controls function correctly. Ideally a single test number that fills all slide control positions should be programmed and checked, but as such a number is unlikely to be available then a series of test numbers will have to be programmed and checked for correct access. The autodial needs to find a number in the FIRST slide control position but it will release if it does not find a number programmed in any of the next 6 slide control position (on in any consecutive 6 positions). The test numbers must be programmed to fill position 1 and other positions with no more than 5 blanks between digits. The following example shows how these requirements can be met using a single "FICTITIOUS" 4 digit test number 2121.

On completion of testing re-enter the customer's required number.

Testing On PABX Installations
When programming for Public Exchange Test Numbers it will be necessary to prefix the test number with the required PABX access digit(s) and to operate the relevant Pause Slide Control. Testing procedure should then follow the general requirement of the testing procedures mentioned above.

A long interdigit pause, following the access digit(s), can be obtained if required, by moving a strap as detailed above.

The following items should be recovered and booked into the stores.

  • Autodial No. 401A
  • Block Terminal 35
  • Switch No. 5A-4

An extract from the memoir's of ex GEC employee Martin Pickering
Taken from his web site

My very first design project at GEC Aycliffe was the "Single Number Callmaker" or "Autodial No. 401A".  The original Autodial was a large box full of cams, cogs and contacts.  When you heaved down on the plunger it set a flywheel in motion that drove the various cams and cogs to open and close the contacts at 10 pulses per second.  It could be "programmed" to dial out a complete telephone number of up to (I think) ten digits.

My job was to design the base and plastic cover mouldings to meet the Post Office specifications.  One problem was that it needed a hinged lid for access to the slide switch matrix but the Post Office boys did not want any visible hinges.  It took me six months to develop an ingenious plastic spring hinge made of acetal copolymer ("delrin") to do the job.  I imagine the total development cost was astronomical and I think we eventually manufactured just a few thousand.  By that time, push-button "MF" (tone) dialling phones were on the drawing board and the Autodial was obsolete.

This electronic replacement "Autodialler" derived all of its power from the telephone line.  The required digits were set by means of a slide switch matrix designed by the "Mechanical Department" (Godfrey Hall) under John Leworthy.  The electronic circuit design was by, as I recall, "Sparky Bob" Stevenson and Maurice Weeks in the Electronics Design department run by "Sam" Crooks.  A custom I.C. was designed to control the operation of the two mercury-wetted relays whose job it was to "loop the line" and provide the pulses.  The I.C. was horrendously expensive to develop and produce.  A ferrite transformer oscillator was employed to take the small current from the telephone line and convert it to a stable voltage supply.

Click here for Martin Pickering

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Internal view



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