Dials, Automatic No. 20

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3 Internal
Issue 1, July 1971


Dials, Automatic, No. 20LA have been introduced to enable users of existing type coin-boxes (Boxes, Coin-collecting No. 14.... ) in a director area to dial the new assistance code "100" without charge. Dials, Automatic, No. 13LA which they supersede, and Dials, Automatic, No. 13FA, permit only 9 or 0 to be dialled free. The additional facility is provided by a special cam to open the contacts of the auxiliary spring-set.

Background information
The assistance code "100" will replace the existing assistance code "0" for Subscriber Trunk Dialling (STD) because "0" will be used as the first digit of the national numbering scheme.

The assistance code "100" will be introduced in advance of S.T.D. to enable subscribers to become accustomed to it. In director areas the code will be extended to coin-box users because of common A-digit selectors, but to do this it will be necessary to change the existing dials to Dials, Automatic, No. 20LA. This can be avoided in non-director areas because the segregation of coin-box lines at the first selectors will enable coin-box users to continue to dial "0" for the operator until the new coin-box (Telephone No. 705), designed for use with subscriber trunk dialling, is introduced. The Telephone No. 705 uses an ordinary subscriber's dial and will render the Dial, Automatic, No. 20LA and the Dial, Automatic, No. 13FA obsolete.

Areas of use
Dials, Automatic, No. 20LA will be used in public call offices and subscribers' coin-box installations in

  • all director areas
  • the fringe areas of the London director area. Their use in these areas is however merely to standardise supplies, and Dials, Automatic, No. 13FA should continue to be used as long as stocks are available

Elsewhere, the Dial, Automatic, No. 13LA will continue to be used in association with Boxes, Coin-collecting, No. 14 ...

Cord connections
These are identical with those of the Dial, Automatic, No. 13.

Introduction to service
Dials, Automatic, No. 20LA should be fitted in all director areas on all new work and when existing dials need to be maintenance exchanged. Supplies are already assured for these two purposes and additional supplies will be obtained as necessary for Areas to complete the change-over as detailed in the next section. It is essential that requisitions for Dials, Automatic No. 20LA should cover immediate needs only, otherwise supplies may be jeopardised. Area stocks should be kept to a minimum.

Completion of dial change-over
When the date for the introduction of the "100" code is known, plans should be made for changing the remaining Dials, Automatic, No. 13LA in the area concerned. Arrangements for the London director area have been made separately, but in the provincial director areas:-

  • commencing 15 months before the due date, an existing Dial, Automatic, No. 13LA should be changed for a Dial, Automatic, No. 20LA on any maintenance visit to a subscriber's coin-box installation.
  • commencing four months before the due date, the remaining Dials, Automatic, No. 13LA should be changed on the routine visits to public call offices. This period should enable all public call office dials to be changed.
  • within the last three months, a planned operation will be required to complete the change of dials at subscribers' coinbox installations.

A change of dial should be recorded on the fault card to enable a check to be made of the installations still requiring attention.

After the dial is fitted, it is not possible to identify it by appearance. It can, however, be identified by dialling "1" without inserting coins. If dial tone is then heard, the dial is a No. 13. A Dial, Automatic, No. 20 will give N.U. tone if the "100" code has not been introduced, or no tone if the "100" code has been introduced.

Disposal of Dials, Automatic, No. 13LA

  • Surplus new Dials, Automatic, No. 13LA should be returned to the Supplies Dept. as soon as possible, packed in bulk and clearly marked as "new and fit for reissue"; otherwise they might be put to old stock and sent to the Factories Dept. for conversion into Dials, Automatic, No. 12
  • Used Dials, Automatic, No. 13LA should be returned to the Supplies Dept. in the normal manner


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Last revised: January 12, 2021