TELEPHONE No. 740


General Information on 700 Type Telephones

How to wire your Telephone No. 740 to make it work on Plug and Socket

How to remove the case

Click here for Additional Buttons N849 - Web users - CD users.

Click here for the Auxiliary Switches N848 - Web users - CD users.

Circuit diagram N840.

Click here for the circuit diagram - Web users - CD users.

Superseded Telephone No. 710


ENGINEERING INSTRUCTIONS
TELEPHONES
STATIONS
A 1076
Issue 2, Feb 1969

TELEPHONES 740 AND 746
Description

General
This Instruction describes Telephones 740 and 746, which are counterparts to the Telephones 710 and 706 and have been developed from the printed wiring version of the Telephone 706. The principal new features are as follows:-

(a) A new design of telephone cover, which now incorporates a carrying- handle.

(b) Use of microswitches for the gravity spring-sets.

(c) Smaller electrical components, with the regulator permanently connected.

(d) Optional provision of one or two press-buttons on the Telephone 746, or four on the 740.

(e) A common chassis for both types of telephone.

(f) A plain outer dial ring matching the telephone cover and used in conjunction with a dial having numbers only on an antique silver background. (During the transition to all figure numbering some telephones may be issued with an outer dial ring, having numbers and letters, which matches the handset.)

Many parts of the Telephones 740 and 746 are identical with those of the Telephones 710 and 706 which are described in A 1063 and A 1060 respectively. This Instruction describes only those parts particular to the Telephones 740 and 746.

The telephones, which as issued are for use in automatic areas only, are suitable for use on lines of up to 1000 ohms T.E.R.

The telephones can be modified for a variety of uses by the fitting of add-on units,' adapters etc. and these will be described in later instructions.

The Telephone 746 is available in black, blue, two-tone green, two-tone grey, ivory, red and yellow. The Telephone 740 is available in black, two-tone grey and ivory only.

Cover
On both types of telephone the cover is secured to the telephone assembly by a lug on the front skirt which engages in a recess in the leading edge of the base and by a single fixing screw located above the cord entry at the rear of the case. The screw, which is held captive by a bush and a spring, engages in a tapped hole in the cord clamp, a T-shaped metal bracket riveted to the rear of the base.

The telephones, as issued, have the aperture for the press-button(s) closed with a dummy button held in place by a clip. When a press-button unit is fitted the dummy button and clip should be secured within the telephone for subsequent refitting.

The outer dial ring fits round the hole in the sloping face of the cover through which the dial protrudes. The dial ring is secured by dropping the lugs on the ring into the recesses provided on the edge of the hole in the case and turning clockwise until the two recesses provided for the finger-stop line up. To remove or refit the ring the cover must be taken off the telephone assembly.

An 'off-rest' position is provided with the handset resting across the instrument just above the dial.

A carrying-handle, in the form of a recessed finger ledge, is provided between the horns directly below the normal handset position.

Base
Telephones 740 and 746 are fitted with a base made of mild-steel with a crackle black-enamel finish. There is a 'knock-out' and three holes in the base for use with a Plan-set N 625 and a cord-entry hole at the rear of the base for a watch receiver, as on the Telephone 706. A ring of slots is punched out beneath each of the bell gongs. Two studs, fixed to the base, support the printed wiring board which is secured by a single screw inserted into a tapped hole raised in the base. The bell gongs are supported by two removable moulded pillars; two long screws pass through the metal plate supporting the dial, the gongs and the moulded pillars into tapped holes raised in the base.

The plunger-supporting brackets are riveted to the base.

Printed wiring board
The main features of the printed wiring board are:-

(a) its reduced size

(b) the regulator is permanently wired in

(c) the gravity microswitch is permanently wired in.

The printed wiring board is located by mating slots in the front edge of the board and in the sides of the plunger-mounting bracket.

The regulator is an integral part of the telephone circuit and provision is not made to render it inoperative.

The gravity spring-set consists of a microswitch positioned alongside the left-hand support of the plunger-mounting bracket. The switch is operated by a lever pivoted on a bracket at the rear edge of the switch cover, the upper end of the lever being formed into a channel in which a projection on the plunger assembly rides. A coiled spring holds the lever in position. The switch is operated when the handset is on the rest.

Dial and dial cord
The telephones are fitted with a Dial, Automatic, 21FA (clear). This has a number ring with black figures on an antique silver background and a transparent finger-plate. The dial cord has spade-tags at one end for connection to the dial terminals and ring-tags at the other for connection to the telephone terminals.

Terminal block and line cord
The Telephone 746 is supplied with a four-wire line cord and a four-way terminal block, the Telephone 740 is supplied without line cord or terminal block.

Bell
A single-coil bell is under development for the Telephones 740 and 746, but early issues will be fitted with a Bell 59C-1. The bell is screwed to the base of the telephone.

Telephone circuit
The circuit for Telephones 740 and 746 shows one change from that of the Telephone 706. The brown wire from dial terminal D3 is taken to telephone terminal T3 instead of gravity spring 5. This short-circuits the transmitter when the dial is taken off-normal and prevents surges in the spark quench circuit passing through the transmitter.

Press-buttons and switches
The press-buttons for use with Telephones 740 and 746 are transparent to obviate the stocking of a range of colours for each type of button and legend. The legends available for each type of press-button are shown in Dgm. N 849.

Press-buttons for the Telephone 740 are provided by removing the dummy button and fitting a Part 1/ ... 10/DBU/372 using the pin, Part 1/DPI/203, provided in the telephone.

A single press-button for the Telephone 746 is fitted by removing the dummy button and clip and inserting a Part 1/ or 2/DBU/362 which is retained by two pins, Parts 1/DPI/203. When two press-buttons are required, two Parts 1/ ... 6/DBU/363 are fitted, each with one Part 1/DPI/203.

Where a single change-over contact (non-locking) is required in association with a press-button in either telephone a Switch No. 5A-4 together with an operating plunger, Part 1/DPL/1022, is fitted. Other non-locking contact assemblies can be provided on either telephone by fitting the spring-sets described in Dgm. N 848 together with a Part 1/DPL/1022.

There a locking single change-over contact is required in association with a, press-button on either telephone a Switch No. 5A-9 is fitted (this switch includes an operating plunger). Other locking contact assemblies can be provided on the Telephone 740 by means of the latch-plate as described in A 1063 and Dgm. N 848.

Additional gravity switches can be fitted to either telephone when required as follows:-

A single change-over  Switch No. 19B-1
Two change-overs  Switch No. 19D-1
Three change-overs  Switch No. 19C-1

Replacement parts
Table 1 lists the replacement parts which are being made available:-

TABLE 1

Part To be requisitioned as:-

Cover (Telephone 740)  Part 1/DCO/723 (colour)
Cover (Telephone 746)  Part 1/DCO/703 (colour)
Outer dial ring  Label 479A
Buttons (feet)  Part 2/DBU/259
Dial  Dial, Automatic, 21FA (clear)
Handset  Handset 3 (colour)
Mouthpiece  Mouthpiece 21 (colour)
Earpiece  Ear-piece 26 (colour)
Transmitter  Transmitter-inset 16
Receiver  Receiver-inset 4T
Transmitter spring  Part 1/DRI/50
Receiver spring  Part 1/DRI/50
Bell  Bell 59C-1 unmounted
Bell gongs  Bell-gongs 24A and 24B
Link (for telephone terminal strip)  Part 1/DLI/20
Links (for terminal block)  Parts 1/DLI/19 and 1/DLI/29
Terminal block (Telephone 746 only)  Block, Terminal, 52A
Handset cord  Cord, Instrument, 4/88AK (colour)
Line cord (Telephone 746 only)  Cord, Instrument, 4/83AA (colour) 72 in.
Dial cord  Cord, Instrument, 5/42L
Printed wiring board with components  Telephone-unit D 92732

References:- A 1060 & A 1063


How to remove a Telephone No. 746 or 740 case

  1. Locate the case fixing screw on the rear of the case above the cords.
  2. Slacken the screw until it becomes loose - it remains fixed to the case, held by a spring and is not completely removed.
  3. Lift the rear of the case upwards and towards the front of the until it is clear of of the dial.
  4. Pull front edge of case forward to release from lip on front of base plate.

Re-fitting is the process in reverse, except you may have to slide the casing dial ring to locate it over the dial.

If the casing screw does fall out - fit back as follows:-

  1. Place spring on screw.
  2. Insert screw and spring into hole in case.
  3. Offer up nut with threaded end case side.
  4. Screw the screw into the nut, until the threaded section is free.

Additional information

ModelMarkBlackGreyIvoryIntroducedRemarks
Tele 740Mk 1yyy2/68Superseded Tele 710L & F - type 1 case
 Mk 1Ayyy2/72Part 4/DCO/923 fitted
 Mk 2yyy10/77Type 2 case & Kit No. 285A fitted
 Mk 1yyy Type 2 case & Kit No. 285A fitted
 Mk 1yyyRefurbishedGrey & Ivory have Cord Inst 4/121 3000mm
 Mk 1AyyyRefurbishedGrey & Ivory have Cord Inst 4/121 3000mm
 Mk 2yyyRefurbishedGrey & Ivory have Cord Inst 4/121 3000mm
Tele 740CMk 1yyy9/79 
Tele 740DMk 1yyy1/80Fitted with high impedance bell
  
 
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Last revised: April 13, 2010

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