First generation battery keyphone - Superseded by the Telephone No. 756 and  Telephone No. 764

3 Internal
Issue 1, Jan 74


This instruction describes and gives information on a 10 pulses per second self-contained keyphone based on Telephone 746.

Telephone SA4274 differs from Telephone 746 in that a push-button unit (PBU) and escutcheon plate replace the dial and outer number ring. A recess is provided at the lower end of the escutcheon plate to take the subscriber's number label. A transparent window strip for the recess is supplied, and is held during transit by a rubber band placed around the telephone.

The PBU occupies the same mounting as the dial it replaces. The pulsing relay is mounted on the left hand side of the gravity switch mounting bracket.

A rechargeable battery is required to drive the PBU circuitry. It is mounted in a plastic clip on the battery bracket, which is located in the holes provided for Strip Connection 155A. Male and female snap connector terminals are provided on the battery, the male being positive.


A six-way terminal strip (TA-TF) is located at the lower end of the battery bracket. Connections are made on this according to the method of battery charging required. An auxiliary gravity switch (Switch 19B-1) is provided to switch the battery from "Charge" to "Discharge" when the handset is lifted.

Telephone Circuit
This is the same as in Telephone 746. The dial pulsing and off-normal contacts have, however, been replaced by relay contacts.

The battery is charged when the handset is on its rest; charging stops when the handset is lifted. At some installations, the battery may be charged by line current from the public exchange or 50v PABX; Kit 196A will be required to control this current. When line charging is not possible, a local power supply will be needed.

KIT 196A
This consists of an electronic circuit on a printed wiring board, two tapped spacing bushes and two captive 8BA screws designed to be mounted on the battery bracket. The purpose of this kit is to disconnect the charging circuit from the line when normal idle conditions are disturbed i.e. when testing from the exchange. After normal conditions have been restored for about 90 seconds, the kit reconnects the charging circuit to line.

With the addition of auxiliary apparatus as required, Telephone SA4274 is suitable for use on Exchange lines (exclusive and shared), PBX extensions (with or without recall) and those extension plan installations which could otherwise be met by the provision of Telephone 746, except for the following,

  • Extension Plan 4 with more than one keyphone.
  • In conjunction with Lamps Signalling Nos.: 1 & 2.
  • Operators instrument on Switchboard PMBX 2/......
  • Installations of high-usage.

If a Telephone SA4274 is required on an extension plan where pre 700 type telephones exist, other than on the extension of extension plans 5, 5A, 7 and 7A using Bell-set 20, 39 or 44, all earlier types of instrument must be replaced by 700 type.


Charging over Exchange lines or 50v PABX extension lines

Exclusive DEL and Extension Plans Line charging should be employed on only one Telephone SA5274 per exchange line using Kit 196A fitted on the following:-

DEL Plan 1A - Main or extension Plan 4 - One portable keyphone only.

Shared Service Lines and Extension Plans Charging facilities are dependent upon the calling equipment used in the exchange.

(a) Uniselector per line, 200 pt line finder, UAX and TXK calling equipment's allow line charging for one Telephone SA4274 on each party.

(b) 50 Pt line finder, TXE2 calling equipment's restrict line charging to one Telephone SA4274 to ONE party only.

Subject to(a) and (b) above, the following application may be met:-

  • Shared service exchange line
  • Plan 1A - Main or extension
  • Plan 4 - One portable keyphone only

50v PABX direct extensions and associated extension plans excluding PABX 1 extensions arranged for direct extension night service, line charging using Kit 196A may be employed for not more than one Telephone SA4274 (per extension line) on the following:-

  • Direct extension
  • Plan 1A - Main or extension
  • Plan 9 - One portable keyphone only

Charging from Existing Local Power Supply This method should be adopted for:-

Main of Plans 105, 105A, 107 and 107A
Two additional connections are required to extend the 12v supply from the plan-set N625 to the charging circuit of the telephone.

Internal Extensions on PMBX 2/..., PMBX 4 and Plan 107
The switchboard or plan-set power supply may be used if more convenient than providing a separate unit as described in the next paragraph. An instrument cord with extra conductors and a larger block terminal may be required.

Charging from Power Unit Provided for this Purpose Except for those listed in para 5, 6.1 and 6.2, all other applications will require the provision of a power unit. In addition, a power unit must be provided in lieu of line charging when switching facilities are provided on the exchange line or extension to divert the line from the telephone to other equipment. Power unit 53A should be used and, if required, up to 80 keyphone batteries may be charged from one power unit. An instrument cord with extra conductors and a larger block terminal than that shown in the appropriate N diagram may be required.

Telephone SA4274 will accept the same auxiliary units as Telephone 746 (see diagram N 848) except Strip Connection 155A and Lamps Signalling Nos. 1 and 2.
When a Clip 90 is required it should be fitted to the battery bracket.

To make a call, lift the handset and, on receipt of dial tone, key in the number one digit at a time. It is not necessary to pause between key operations while a digit is pulsed out, unless an access digit is keyed in which case dial tone must be obtained before proceeding.

For information see diagram SA(L) 4274.

When Power Unit 53A is required it should be installed in accordance with C3 Q0020.

Ensure that the handset is replaced properly on the rest, otherwise the battery drain will be excessive and the keyphone will fail to operate correctly. For the same reason, the extension Plan 4 keyphone should always be left plugged into the line socket.

The pulsing of Telephone SA4274 is identical to that of a normal dial telephone and can be tested for speed and ratio in the normal manner.

Should the Switch 19B-1 need to be changed, the helical spring joining the operating lever to the gravity switch arm should be re-connected to the new switch.

When Power Units are installed Fitters should check the charge current at each telephone by disconnecting the red wire from the positive battery terminal and connecting the positive lead of meter multi range to this wire. Connect negative lead of the meter to the battery terminal. With the plungers of the gravity switch depressed a charge of 1-3 milliamps should be observed.

The telephone can be identified from later keyphones by the press buttons.  These have a transparent plastic top with numbers underneath.

The battery is a DEAC type 150DK with a capacity of 150mah.


Model Mark Grey Introduced Remarks
Tele SA4274 Mk 1 y 11/71 Original
Tele 1/SA4274 Mk 1 y 11/72  

  Obsolescent in 1982

Made by GEC

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Last revised: December 17, 2019