3 Internal
Issue 1, Mar 1972


This Instruction describes the 4 types of telephone which have been developed to meet the telephone requirements of PABX's having MF signalling capability.  One instrument is based on Telephone No. 746, two are based on Telephone No. 740, and one based on Loudspeaking Telephone 4D.  In each type of telephone the dial has been replaced by a Push-Button Unit No. 4...  The push-button unit is associated with a multi-frequency line powered oscillator.  When any button is fully depressed, two discrete frequencies are sent to line.  There is a differing frequency combination depending on the button depressed.

As the number of spare telephone terminals available is less than in a normal 700 type telephone, an additional six way terminal strip has been provided.  These terminals are numbered 20-25 inclusive.

As supplied, the telephones are not equipped to provide recall.  This facility can be provided by fitting a Switch No. 5A-4 and associated press button assembly.

Telephone SA4258
This instrument is similar in appearance to the Telephone No. 746.  It is primarily intended as a direct PABX extension, but can house 2 add on press buttons.  A four way instrument cord and block terminal is supplied.

Telephone 2/SA4258
Similar in appearance to Telephone No. 740, this instrument is used when 3 or more press buttons a-re required.  It is also fitted with two lamp opals and Lamp Fittings No. 16A.  The lamp holder wires are terminated on terminals 20-24. Lamps are not included, but a suitable 12 volt 0.02 amp lamp is Lamp No. 48A.  It is intended the lamps should be powered from a Power Unit No. 53A.  A cord instrument is not supplied.

Telephone 3/SA4258
Wall telephone for use on Plan 1A working and PABX extensions.

Telephone 4/SA4258
A wall mounting telephone suitable for direct cabling.  It is electrically and mechanically identical to Telephone 2/SA4258. A wall mounting bracket is supplied with each telephone.

Each type of telephone is fitted with a Push-Button Unit No. 4 .... The push-buttons are arranged in 3 columns of 4.  The 11th and 12th button tops are marked * and # respectively.  The * and # buttons are required for providing additional facilities in the future, and serve no purpose at present.  Depression of either of these push-buttons will send a combination of tones to line, but current PABX equipment will not respond to these signals.

The 2 variants of the Push-Button Unit No. 4 used on Telephone SA4258 are as follows (see table for updates):-

  • PBU No. 4A is fitted in Telephones SA4258 and 2/SA4258.

  • PBU No. 4B is fitted in Telephones 4/SA4258.

This is a combination of audio tones that can be heard in the receiver when a push-button is depressed.  Its intention is to give the user an indication that the call is proceeding satisfactorily during the keying period.  The tones will vary in frequency, depending on the button pressed.

Each of the telephone circuits, together with the extension plans in which Telephone .... /SA4258 may be used, is shown in Diagram SA(L)4258.  It should be noted that all extension plan titles are prefixed by the letters K MF, i.e. Plan 107 becomes Plan K MF 107.  This is to prevent confusion with orthodox extension plans.  The K MF denotes that a keyphone is being used, using a multi-frequency signalling principle.

The above diagrams are not available through general circulation. If required, requisitions should be submitted in the normal manner.

All variants are produced in the standard seven colours.

Circuit diagram - SA/SAW 4258.

Drawings - 93224 and 93226.

Specifications - S1106 and S1300.


Model Mark PBU Introduced Remarks
Tele SA4258 Mk 1   2/69 Plessey
  Mk 2 7A 3/74 GEC
  Mk 3 8 9/75 Plessey (not used)
  Mk 4 8 5/76 Plessey - replaced Mk 3
  Mk 5 7A 5/76 GEC
Tele 2/SA4258 Mk 1 4A 12/71  
  Mk 2   3/74 GEC
  Mk 3   10/74 Conversion of 4/SA 4258
  Mk 4 8 9/75 Plessey
  Mk 5   5/76 GEC
Tele 3/SA4258 Mk 1   12/71  
Tele 4/SA4258 Mk 1 4B 12/71 Plessey
  Mk 2   3/74 GEC
  Mk 3 8 9/75 Plessey - Not used
  Mk 4 8 5/76 Plessey - Replaced Mk 3
  Mk 5   5/76 GEC
Tele 5/SA4258 Mk 1   9/74 Not proceeded with (see 2/SA4258 Mk 3)


New Zealand also used the SA4258 and the one pictured below is probably a NZPO Model HC403.

The telephone was made in 1975 by GEC and probably a Mark 2.

Located in New Zealand Museum of Transport and Technology - Telephone [Push Button], 2019.108.7.



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Last revised: February 18, 2023