GEC
KEYPHONE 89

G.E.C. KEYPHONE 89
For Loop Disconnect Signalling

KEYPHONE 89 offers a simple means of providing a pushbutton telephone system without incurring high capital investment.

KEYPHONE 89 does not require any special exchange equipment: it suits exchanges that accept loop-disconnect signalling.

KEYPHONE 89 uses many components standard to the GEC746 series of telephones.

KEYPHONE 89 adaptor kits are available to convert rotary-dial GEC746 telephones already in service.

KEYPHONE 89 accepts up to 20 digits (to allow for STD and ISD calls) and transmits them as loop-disconnect pulses at 10 IPS, complete with the appropriate make-to-break ratio and inter-digit pause.

KEYPHONE 89 can be freely used in combination with rotary - dial telephones in extension-telephone systems.

KEYPHONE 89 does not use relays: high-voltage transistor switches generate the loop-disconnect pulses. (Transient high-voltage suppression is included to prevent damage to the transistors during lightning or other induced surges.)

KEYPHONE 89 does not use a battery: the electronic circuits are powered direct from the exchange supply using an internal storage capacitor as the power source during impulse periods.

KEYPHONE 89 keyset is an established high-reliability design, proven in telephone service.

KEYPHONE 89 pushbuttons have a 'fall through' action to ensure positive operation. The contacts are gold plated and enclosed to protect against dust.

KEYPHONE 89 button shape minimizes incorrect number selection - the angled sides and recessed top face assist finger location.


Keysender Unit	Internal view of Telephone


Press Button view

Data Summary

Exterior
Case and handset moulded in ABS high-impact plastic. Seven colours are available: ivory, yellow, dual grey, dual green, red, blue, and black (in dual-colour telephones the handset and the cords are the darker tone).

Cords
PVC-covered cadmium-tinsel conductors. Held in position by stress-relieving grommets.
Line cord, straight: 2000 mm (78 in)
Handset cord, coiled: 200 mm (8 in) unextended; 1700 mm (68 in) extended.

Signalling
Keypad -10-button keypad with black numerals on a white background; the buttons are arranged in the 3+3+3+1 format to CCITT recommendations. Each button has a 'fall through' action (resistance to applied pressure decreases as the button is displaced) to ensure positive operation. Button travel is 4 mm (0.156 in). Button contacts are enclosed to provide protection against dust.

Store - accepts 20 digits keyed in as fast as the user wishes; metal-oxide semiconductor (MOS) integrated circuits used. The information keyed into the store is converted to a series of loop-disconnect pulses for transmission over the normal telephone line.

Impulse speed -10 + 1 IPS in the temperature range -10 to +50 degrees C and line range 0-15000 loop resistance. Impulse ratio: 66.6% break-to-make. An alternative version having a 60% break-to-make ratio is available. Impulse distortion is maintained within rotary-dial limits.

Interdigit pause - 800 ms nominal. An alternative 1000 ms interdigit pause version is available.

Line loop current - the keyset will operate satisfactorily over the line loop current range 15 mA to 120 mA.

Line loop currents of up to 200 mA, which can occur during operation of the recall button, will not damage the keyset.

Transducers
Receiver inset - rocking armature; replaceable capsule; sensitivity +56 dB relative to 1 VPa/W.
Transmitter inset - carbon granule, replaceable capsule; sensitivity -10 dB relative to 1V/Pa at 2 Pa input.

Regulator
A built-in automatic volume regulator limits speech-signal amplitudes on lines shorter than 400 ohms; virtually no attenuation on longer lines.

Ringer
Double coil; DC resistance 1000ohms, impedance at 25Hz 2000ohms, impedance at 1000Hz 20k ohms; accepts ringing currents of between 16 and 30 Hz; bells, double-gong harmonizing tones; bell-volume control.

Environment
Suitable for all climates; protected against the entry of insects.

Dimensions and Weight
Height: 119mm (4.75in) Width: 250mm (10in) over handset; 140mm (5.5in) over case.
Depth: 216mm (8.5in) over case.
Weight: 1.7kg (3.5lb) complete telephone; 230g (8oz) handset.

Take from The GEC Catalogue Leaflet 5mF476 (Dated 1976)

This model is self contained and does not require a battery.

Used by the UK Post Office as their Telephone SA 10186.