For use on existing magneto, C.B.S. or C.B. systems, this instrument is designed to save the expense of replacement when systems are modernised. It can be supplied with connections appropriate to any of the following conditions and is readily convertible to any other as required.
(1) Magneto, with or without 0.5mFcapacitor in the receiver circuit.
Stock instruments are in tropical finish and include a transistor generator, wiring for both a dial and a plug-in regulator, a 5000 ohm ringer and capacitors within the ringer and receiver circuits. A diagram is supplied with each instrument, indicating the various strapping adjustments and equipment requirements (where necessary) for conversions 1 to 10 above. Conversions do not affect the induction coil.
The Etelphone range combines high performance with attractive appearance and wide application. It includes the basic instrument designed in conjunction with the British Post Office and caters for the following requirements:-
The transmission circuit ensures maximum frequency response and line sensitivity over exchange lines with loop resistances up to 1000 ohms. It employs a conventional hybrid transformer with a fixed balanced network and includes the following standard components:-
Ringer with coils wound to any specified resistance. The latest ceramic magnet material is used in conjunction with a pressed-iron frame to obtain high, stable performance with simplicity. A simple wire biasing-spring can be fitted to eliminate bell tinkle when the instrument is used on party lines.
Transducers of sealed capsule type.
Contact springs tipped with precious metal contacts to ensure maximum contact reliability.
Internal conductors are insulated with p.v.c., a material fully resistant to moisture, attack by insects and fungoid growth. Desk and handset connecting cords are additionally protected by p.v.c. sleeving. External conductors terminate on screw terminals on the instrument terminal field.
The dimensions are common to all versions of the Etelphone, being 11 in. x 9.25in. x 5.5in. (279 x 235 x 140mm); the weight varies between 3 and 4.6lb (1.3 and 2.1 kg).
Taken from the Plessey Telecommunications Publication No. 7099 (1/69)
Last revised: October 04, 2019