Prestafone
Press Button Telephone
Mark VCatalogue No. T151
 The
Prestafone self-contained pressbutton telephone operates with telephone
exchanges normally receiving loop disconnect pulses. It is connected
for press-button service in the same way as a normal dial telephone.
The facility of pressbuttons is, therefore, now available to users anywhere
without the complications of telephone exchange (central office)
modifications.
The Prestafone Mark V is battery-less and uses all electronic switching
for increased reliability.
The electronic circuits of the Prestafone contain a metal oxide
silicon - large scale integrated (MOS-LSI) circuit which both stores the
inputs from the buttons and also generates the outgoing pulses to a high
degree of accuracy. Buttons may therefore be pressed as fast as one wishes
whilst the telephone set will pulse out at the correct speed.
A ringing volume control is fitted and is operated by adjusting a lever
conveniently positioned at the front and below the body moulding.
Use of the MOS - LSI circuit and electronic switching ensure accuracy of
operation and a high degree of reliability in all environments.
Good looks form an essential part of the basic design which is a
development of the Pye TMC 1746 Series telephone. Features include a case
moulded in shock and scratch resistant ABS plastics which incorporates an
integral carrying handle. The handset contains the same high sensitive
transmitter and receiver inserts as the standard 1746 telephone. All units
are finished to a full tropical specification.
The Prestafone is available in the following colours: Red, Blue, Two-tone
Green, Two-tone Grey and Ivory, thereby affording a choice to suit every
decor. Instruments may be fitted with recall/earth buttons for working on a
PABX. Variations to meet other requirements (plan arrangements) etc. are
also available.
Dimensions/Weight
Height (over handset) - 127 mm.
Width (over handset) - 237 mm.
Depth - 216 mm.
Handset cord normal - 254 mm / extended - 1.70 m.
Instrument cord 3m.
Weight - Telephone 2 kg.
Weight - Handset additional 280 g.
Technical Data
Pressbutton module
Keypad
Comprises ten keys laid out to CCITT recommendations. The keys are
white with black digits. Each key operates a 'collapse-action'
gold-plated double contact.
Micro-electronics
MOS-LSI circuit.
Storage
Static capacity 18 decimal digits. Cyclical storage feature extends
effective storage capacity.
Speed
10 P.P.S. ±3%. Other speeds and pulse ratios can be provided against
specific requirements.
Ratio
1.6: 1 or 2:1.
Distortion
Less than 3.0 ms initially and less than 4.0 ms with ageing.
Inter-train pause
840 mS.
Rate of dialling
Digits may be selected at intervals of not less than 40 mS.
Power
Line powered, no internal battery required.
Transmitter
Carbon granule replaceable capsule type. The change in sensitivity
over the input range 3-30 dynes per sq. cm. is less than 5 dB at a given
frequency in the range 300-3400 Hz.
Receiver
Rocking armature, replaceable capsule type. The receiver has a mean
sensitivity of +46 ±2 dB relative to 1 dyne per sq. cm. per VmW of available
power when tested with an artificial ear.
Automatic regulator
This feature is used to eliminate the excessive sound levels and sidetones
which may be encountered on short lines because of the high efficiency of
the latest receivers and transmitters. Maximum sidetone attenuation and line
attenuation (6 dB send, 4 dBreceive) are provided on short lines and these
attenuations progressively reduce as line loop resistance increases to 400i
when they become negligible.
Casing
The handset and case are moulded in a copolymer of acrylo-nitrile, butadiene
and styrene (ABS) having high impact and tensile strength and excellent
colour fastness.
Ringer
Double coil, resistance 1,000 ohms impedance ranging to 20k ohms at 1,000
Hz. Ringing current frequency range 15 to 30 Hz.
A ringing volume control is fitted and is operated by adjusting a lever
conveniently positioned at the front and below the body moulding.
Line conditions
This telephone is suitable for use on lines having a loop resistance ranging
from zero to more than 1250 ohms and exchange battery voltages varying from
44V to 52V.
Taken from Publicity Leaflet AA/1.75/2 SEA (dated 1975)
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