Switches for Telephones
Telephone No. 8746
- Telephone No. 746 modified for PST working with plug ended line cordGeneral Information on 700 Type Telephones
How to wire your Telephone No. 746 to make it work on Plug and Socket
How to remove the case -
Click here for the later variant with bell volume
control and Unicoil bell
Click here to hear a Telephone No. 746 bell
Diagram for Additional Buttons - N849.
Diagram for the Auxiliary Switches - N848.
Diagram for the telephone circuit diagram - N846.
Click here for the colour range
|Early cased model - note
sloped case under handset
||Later cased model - note
recess in top of case for handset
In 1967 the 746 Type telephone was introduced (See also Telephone
No. 736). This was an improved version of the 706 range and offered similar facilities. The case styling is slightly different from the
Telephone No. 706 although it retains the same overall look. The
case now has an integral handle which obviates the need for a separate handle (the
Telephone No. 706 plastic handles used to break).
Unlike the Telephone No. 706, this phone could also have two switches fitted.
The oblong dummy plate above the dial is removed and a single transparent
plastic plunger or two half size plungers could be installed.
Originally the case had a slope from above the dial, sloping backwards, under
the handset, finishing at the raised handset stops to the rear of the
case. This design was found to allow the handset to sometimes slide
forward and this was sometimes enough to allow the switchooks to operate - thus leaving the phone off
hook. The case was later modified and the handset now rests in a recess,
with raised sides to stop the handset sliding forward. The pictures above
show both the early and later style cases.
Inside the circuitry is different in that the regulator components are soldered directly onto the printed circuit board, the switch-hooks and other components were miniaturised. No conventional wiring version was produced. The same colour options as for the 706 were offered to the customer.
The Telephone 746 was later produced with the new style plug type lead (PST and renumbered as the Tele 8746) and converted to high impedance bells.
A brown version was introduced and telephone
746 range was then marketed as the 'Yeoman '.
Access to the insides is via a
single self retained screw on the rear of the case.
Undo the screw until it goes slack - do not remove the screw completely!
Do not remove any of the screws in the base unless you wish to remove the bell
gongs and bell ringer.
Available to all customers in 1970 and supplied into the late 1980's as maintenance stock.
phones and refurbished phones had the Transmitter No. 16 replaced by the
Transmitter No. 21 (blue or red variants) due to transmitter noise issues.
Issue 2, Feb 1969
TELEPHONES 740 AND 746
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.
(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.
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.
A phone with the single switch is shown to the right.
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.
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.
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.
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 and is now superseded by Switch No. 23A). 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:-
Table 1 lists the replacement parts which are being made available:-
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
- Locate the single case fixing screw on the rear of the case, just above the cords.
- Slacken the screw until it becomes loose - it remains fixed to the case,
held by a spring and is not completely removed.
- Lift the rear of the case upwards and towards the front of the until it is clear of of the dial.
- 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:-
- Place spring on screw.
- Insert screw and spring into hole in case.
- Offer up nut with threaded end case side.
- Screw the screw into the nut, until the threaded section is free.
|This picture shows the later style of auxiliary
switch installed correctly
||This picture shows a standard
|Tele 746||Mk 1||y||y||y||y||y||y||y|| || || |
| ||Mk 1A||y||y||y||y||y||y||y|| || || |
| ||Mk 2||y||y||y||y||y||y||y|| || || |
|Tele 746A||Mk 1|| ||y||y|| || || || || ||2/73||
Ivory introduced 1/76|
|Tele 746B||Mk 1||y||y||y||y||y||y||y|| ||10/78||Not preceded with 5/79|
| ||Mk 2||y||y||y||y||y||y||y|| || ||Adjustable bell|
|Tele 746BR||Mk 1||y||y||y||y||y||y||y|| ||12/78||ELR button & bell 79A|
| ||Mk 2||y||y||y||y||y||y||y|| || ||ELR button & bell 59A|
|Tele 746C||Mk 1||y||y||y||y||y||y||y|| ||9/79|| |
|Tele 746CR||Mk 1|| ||y|| || || || || || ||9/79||Tele 746C with ELR|
|Tele 746D||Mk 1||y||y||y||y||y||y||y|| ||1/80||High impedance bell|
|Tele 746F||Mk 1||y||y||y||y||y||y||y|| || || |
| ||Mk 1A||y||y||y||y||y||y||y|| || || |
| ||Mk 2||y||y||y||y||y||y||y|| || || |
| ||Mk 3||y||y||y||y||y||y||y|| || ||
Single coil bell|
| ||Mk 1|| ||y||y|| || || || || || ||Refurbished|
| ||Mk 2|| ||y||y|| || || || || || ||Refurbished|
|Tele 746L||Mk 1||y||y||y||y||y||y||y|| || || |
|Tele 746R||Mk 1|| ||y||y|| || || || || ||8/73|| |
| ||Mk 1A|| ||y||y|| || || || || ||9/73||Part No 3/DCO/703|
| ||Mk 2|| ||y||y|| || || || || || || |
| ||Mk 1|| ||y||y|| || || || || || ||Refurbished|
| ||Mk 1A|| ||y||y|| || || || || || ||Refurbished|
|Tele 746S||Mk 1|| || || || || || || || ||5/79||Field trail
|Tele 746SR||Mk 1|| || || || || || || || ||7/79||Field trial
|Tele 746T||Mk 1|| ||y||y|| || || || || ||9/79||Obsolete 3/83 (Plessey)|
|Tele 746W||Mk 1|| ||y||y|| || || || || ||2/73||Field trial control item|
The Telephone No. 8746 can be found in C, D, F, G, GR and R variants.
The GR and R variants were fitted with Earth recall switches. All these
models date from 1981 onwards.
Telephone 8746F has a Bell 59C-1 (1000 Ohm D.C. Resistance).
Telephone 8746G has a Bell 59D-1 (4000 Ohm D.C. Resistance).
Telephone No SA 4284
Tele SA 4284 is a Tele No. 746 used for Teleprax working. The Tele No. 746F is modified for buzzer calling and 6v working.
|Tele SA4284||Mk 1|| ||y|| ||y||y||y||y|| ||11/72||Teleprax working|