AUTO, CB or MAGNETO
Every requirement for a weatherproof telephone for traction routes, building sites, etc., is met in the design of this instrument for wall, pole or post mounting. These requirements include compactness, light weight, robustness, durability, high-quality transmission, low cost, low maintenance liability, and security against unauthorised use. Provision for an operator recall press button when specified is made in the auto and c.b. telephones.
Electrical characteristics equivalent to those of the Etelphone ensure wide frequency response and volume efficiency over lines of up to 1000 ohms loop resistance.
The use of materials liable to corrosion is avoided. The enclosure, consisting of a base, a body and a hinged door, is of corrosion resistant aluminium alloy; other parts are of brass, phosphor-bronze and high-quality stainless steel.
The body is a robust aluminium alloy casting, webbed to form a solid internal shelf for the handset and drilled as necessary for the dial and/or press button. Two screws inside the body secure it to the base, on which the remaining components are mounted.
The door is another aluminium alloy casting has brass hinges and a phosphor-bronze catch. It is channelled to mate with the rim of the body so that foamed Neoprene in the channel excludes moisture when the door is shut. The automatic catch is plunger-controlled, a single motion of the hand sufficing to release it and flip open the door. Self-closing doors, and doors equipped with locks are available to special large-quantity order.
The stove-enamelled hard-aluminium-alloy base, with three hollow bosses on its underside for mounting purposes, fits well inside the telephone body and compresses a foamed Neoprene strip to make the joint weatherproof. Two brass bosses threaded for 0.75in (19mm) dia. conduit are attached to the bottom of the base for the entry of external wires. For magneto working, a cast aluminium-alloy enclosure for the batteries is fixed to the bottom of the base; the conduit entries are then in the bottom of this auxiliary enclosure, and the incoming wires connect to a terminal block from whence they are permanently wired through an insulated hole into the telephone base.
Installation and Maintenance
Installation is facilitated by the telephone body being separate from the base, enabling the base to be fixed and the external wires terminated before the body is attached.
For maintenance, the body-fixing screws are released, the door is then closed to protect the handset, and the body lifted down to hang suspended from the base by the nylon cord provided. Thus all components and wires are accessible.
For pole fixing, a simple form of non-slip adapter is supplied, consisting of a suitably drilled plate with two stainless-steel worm clips. These are available in three sizes and adjustable to suit poles between 3in and 12in (76mm to 304mm) diameter. The post-fixing adapter, suitable for mounting on a 2in (5l mm) diameter post, consists of a spigot mounting casting of aluminium alloy, with vertical telephone mounting plate.
Components and Finish
Components similar to those in the Etelphone and therefore of proven reliability are used. The handset, with temperature resistant coiled cord, is moulded in high-impact plastic. The handset is held in position by a stainless steel 'rest' at the receiver end and a phosphor-bronze clip at the bottom.
The dial number-ring has black characters on a white ground. Unless otherwise specified, dials have standard numbering and a 2:1 break/make ratio. The stainless-steel 4in (101 mm) dia. ringer gongs are mounted on the underside of the base so that signals can be clearly heard.
A transistor ringing-current generator is contained within the magneto version and actuated by simple depression of a switch. A box for four ordinary torch cells is fitted at the lower end of the telephone.
Apparatus finishes are suitable for the tropics, and connecting wires are insulated with p.v.c., which is impervious to moisture and not subject to mould growth or insect attack.
The front of the telephone displays a raised silhouette of a handset in light grey to contrast with the darker background colour. The general interior and exterior hammer finish of the body is light-grey stoved enamel.
|N1240A||Auto without press button|
|N1241A||Auto with press button|
|N1242A||C.B. without press button|
|N1243A7||Railway - Half barrier|
|N1243A9||Railway - Half barrier (no cover)|
|N1244A||Magneto - with generator box attached to bottom of telephone|
|N1245A||Magneto - Transistorised|
|N1245C||Magneto - Transistorised (battery box attached)|
|N1247A||Railway - Barrier Omnibus (no cover)|
|N1247B||Railway - Omnibus (battery box attached to bottom of telephone)|
|N1248A1||Automatic with dial - GPO Telephone No. 745|
|N1250A||Department of the Environment - no dial|
|N1254A||Automatic with press button dial pad|
Taken from the Plessey Telephone Publication No's 7037 (1969) & 7183 (1971)
Wiring Diagram for N1240
Wiring Diagram for N1240A1
Converting to work in the UK
Remove link between terminal 13 and 14.
Ensure that terminals 7, 8, 9 and 10 are linked together.
Replace the link between terminals 19 and 20 with a 3.3k resistor.
Ensure that terminals 17, 18 and 19 are linked together.
Connect the red wire of the line cord to terminal 13.
Connect the white wire of the line cord to terminal 10.
Connect the blue of the line cord to terminal 18.
Connect a rectifier element across terminals 24 and 25 if not fitted already.
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