Press Button Telephone
Mark III

Catalogue No.T150

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 electronic circuits of the Prestafone contain metal oxide silicon - large scale integrated (MOS-LSI) circuits which both store the inputs from the buttons and also generate the outgoing pulses to a high degree of accuracy.  Buttons may therefore be pushed as fast as one wishes whilst the telephone set will pulse out at the correct speed.

Use of the MOS - LSI circuits ensures 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.

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.

Dimensons / Weiqht
Height (over handset) - 127 mm.
Width (over handset) - 237 mm.
Depth - 216 mm.
Handset cord normal - 254 mm. / extended - 1.70 m.
Instrument cord - 1.83 m.
Weight - Telephone 2 kg.
Weight - Handset additional - 280 g.

Technical Data

Push Button Module
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.

MOS-LSI circuits.

Static capacity 18 decimal digits.  Cyclical storage feature extends effective storage capacity.

10 P.P.S. 3% or 20 P.P.S. 3%. Other speeds and pulse ratios can be provided against specific requirements.

16: 1 or 2 : 1

Less than 0.5 ms initially and less than 075 ms with ageing.

Inter-train pause
850 ms or 425 ms.

Rate of dialling
Digits may be selected at intervals of not less than 15 ms.

Line powered rechargeable nickel-cadmium battery in telephone.

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.

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 dB receive) are provided on short lines and these attenuations progressively reduce as line loop resistance increases to 400 ohms when they become negligible.

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.

Double coil, resistance 1,000 ohms impedance ranging to 20k ohms at 1,000 Hz.  Ringing current frequency range 15 to 30 Hz.

Line conditions
This telephone is suitable for use on lines having a loop resistance ranging from zero to more than 1,000 ohms and exchange battery voltages varying from 46V to 52V.

Taken from Publicity Leaflet AA/5.74/7M (dated 1974)

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Last revised: February 04, 2019