Convertible telephone, with provision for four press buttons and transistorised ringing generator.
See also N2188
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:-
1. Auto, c.b., or magneto working.
2. Conversion from c.b. to auto working.
3. Conversion from auto to c.b. working.
4. Conversion from magneto to auto or c.b. working.
5. Conversion from table to wall mounting and vice versa.
6. Line performance regulation.
7. Press button for additional switching or signalling functions.
8. Tropical finish with components specially finished and treated to withstand extreme climatic conditions.
9. Amplified handset for users with impaired hearing.
10. Ringer volume control.
11. Unauthorised call restriction by a key-operated dial lock.
All versions are similar in external design and available in a range of pleasing light-fast colours: black, ivory, concord blue, topaz yellow, lacquer red, two-tone green and two-tone grey. The instrument case and handset mouldings are of ABS copolymer, a high-impact material impervious to cosmetics, inks, oils and most chemicals. Table telephones are complete with a moulded desk connecting block in matching colour and both table and wall instruments feature a convenient off-hook position for the handset.
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.
Induction coil with high anti-sidetone properties.
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)
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