voice-switched loudspeaking telephone
- hands-free operation
- all Post Office and p.a.b.x. lines up to 1000 ohms
- fully semiconductored
- full range of 710 switching facilities can be included
The LST4 loudspeaking telephone allows the busy executive complete freedom to refer to correspondence, or make notes, while continuing the telephone conversation. It also enables any number of people who may be in the executive’s office to join in a conversation, and a conference can take place as though the distant party were in the same room.
To bring the telephone into use, a single on/off switch is operated; the LST4 is then used in exactly the same way as a conventional
telephone, without the need for a handset. A three-step volume control caters for widely varying received signal strengths and ensures that on faint calls the distant party has no difficulty in making himself heard.
From left to right, the panel contains: loudspeaker; dial; on/off push bar with indicator lamp below; four pushbutton switches (three for volume, one for ‘Microphone off’) with provision for four button positions above to incorporate additional switching facilities when required; and microphone. A handset is provided so that the
executive can receive confidential messages.
|TEL/6L Face view
|TEL/6L overhead view
|TEL/6L interior view - top cover
The case and front panel are aluminium, finished in dual grey; an alternative version can be supplied with sapele or teak top panel and feet. The pushbuttons, microphone and loudspeaker surrounds, and the handset are moulded in dark grey plastic.
The LST4 operates on lines of up to 1000 ohm line-loop resistance.
With a sound pressure level at the microphone of +92 dB relative to 0.0002 dyne/cm2 at 1000 Hz, the signal level into a 600
Ohm line is -6 dB relative to 1 volt r.m.s.
When energized from a 600 0 source at -18 dB relative to 1 volt r.m.s. at 1000 Hz, the power into the loudspeaker is not less than
1.2 mW; the medium and high volume settings increase the power to not less than 12 mW and 120 mW respectively.
With no signal at the microphone, an input of -44 dBV at 1000 Hz from the line causes the telephone to switch to receive.
With no signal from the line, a sound pressure of +57 dB relative to 0~0002 dyne/cm2 at 1000 Hz causes the telephone to switch to send.
On low and medium volume settings, the telephone remains switched to the last speaker; on the high volume setting, the telephone reverts to the receive condition.
An automatic volume regulator is fitted that limits the speech signal amplitudes on lines shorter than about 400
Ohms; it introduces virtually no attenuation on longer lines.
Rocking-armature tone caller; d.c. resistance 1000 Ohms; impedance 2000 Ohms
at 25 Hz, 20k Ohms at 1000 Hz; accepts ringing currents of between 16 and 30 Hz.
PVC-covered cadmium-tinsel-conductor cords, coloured dark grey. Held in position by grommets to relieve the conductors of stresses.
Speed: 10 p.p.s. Break-to-make ratio: 2 to 1, other ratios can be supplied. Finger plate is clear plastic; number disc characters are printed white on a dark-grey background.
A non-locking pushbutton switch, adjacent to the volume buttons enables the executive to switch the microphone off when
he desires to hold a conversation that cannot be heard by the distant party.
A handset is provided for confidential conversations. Lifting the handset from its rest at the rear of the telephone automatically
disconnects the microphone and loudspeaker.
Extension Loudspeaker and Microphone
An extension loudspeaker and microphone are available which enable the LST4 to be used in large rooms such as conference rooms.
Auxiliary Switching Facilities
All the facilities offered by the 710 plan-switching system, in addition to shared-service, etc., can be incorporated in the LST4. The buttons required to provide these facilities replace the dummy buttons above the volume buttons.
The telephone will operate within the ambient temperature range -10 to +40°C; it meets the requirements for operation under damp-heat conditions set out in British Standard
BS2011, part 1, section 6.2, humidity class 21.
The amplifier and switching circuits require a 50-volt (nominal) 330-mA d.c. supply, ripple not to exceed 1.5 mV r.m.s. (either a
nominal 50-volt exchange battery, via a separate line pair, or a mains-operated power unit, G.E.C. type 98300).
Dimensions and Weight
Height: 165 mm (6.5 in)
Width: 435 mm (17.25 in)
Depth: 216 mm (8.5 in) excluding handset 280 mm (11 in) including handset
Weight: 7.25 kg (16 lb) including handset - 280 gm (10 oz) handset only
Taken from the GEC-AEI Catalogue Leaflet No. STL 25B