Overview
A fascinating and increasingly uncommon GPO (General Post Office) Speakerphone 4 (Loud Speaker Phone LST Model 4D in this case) dating from the late 1960s or early 1970s, some time before the creation of British Telecom (this model was introduced in 1967). This was a high-end executive conference telephone designed for hands-free office communication at a time when such equipment was both expensive and technically advanced.
Unlike an ordinary desk telephone, the Speakerphone 4 contains a substantial electronic amplifier and switching circuitry, allowing conversations to take place without lifting the handset. It represents an interesting stage in the development of business telecommunications and is now a scarce survivor of the GPO era.
This unit is sold strictly as spares, repairs or a collectible display piece. I have carried out only limited functional testing and have deliberately not connected it to a modern telephone line.
Condition
Overall cosmetic condition is very good for its age. The cabinet is clean with only the normal signs of careful use and has survived remarkably well.
The fixed support post for the handset on one side of the cradle is missing and appears to have broken away at some point. The moving cradle remains present and still operates the internal hook switch. A replacement support could probably be reproduced by someone with access to a 3D printer and secured using epoxy resin or a similar adhesive. We know what the other support looks like because the device featured in the 1970s thriller, “If It's a Man - Hang Up!”, see final photo.
The clear dial label cover is still present, allowing the buyer to create and fit a personalised number insert if desired.
Front Panel & Controls
I have tested the front panel controls mechanically. The power switch, volume controls and microphone switch all operate as expected.
The four upper push-buttons fitted to this example are blanking inserts rather than functional switches. Having removed the cover and examined the mechanism, there are no switch assemblies fitted behind these positions.
Also included is the original GPO packet of spare button caps labelled "Spare Parts Should Be Retained With The Telephone". My understanding is that these were supplied for future expansion of the telephone should additional switch modules be fitted, rather than being replacement buttons for the existing panel. It is a nice original accessory that has remained with the telephone throughout its working life.
Connections
The rear panel is fitted with two 3.5mm jack sockets; one for an extra microphone, and one for an extension speaker. I cannot guarantee their function.
The original connection block is included, although its protective cover is missing.
Electrical Notes
Unlike a conventional desktop telephone, the Speakerphone 4 contains a considerable amount of electronic circuitry, including capacitors and other components that are now approximately fifty years old. Whilst telephone systems operate at relatively low voltages, I have deliberately not plugged this unit into a modern BT telephone socket because age-related electronic faults could potentially damage the equipment or affect the telephone line.
Any buyer intending to return the unit to service should expect to inspect, test and possibly replace age-related electronic components before attempting to use it.
It should also be remembered that many modern telephone exchanges no longer support pulse (rotary) dialling, so compatibility with current telephone services cannot be assumed.
Reading some online details about this, it appears to require a 50V input, and may not work with standard telephone lines until this voltage has been addressed.
Included
- GPO Speakerphone 4
- Original connection block (cover missing)
- Original packet of spare button caps (they will be found inside the device, in a plastic bag)
Please study the photographs carefully as they form part of the description and show exactly what is included.
Historical Interest & Collectibility
This mid-century GPO Speakerphone 4 is far more than simply a rotary telephone. It represents the transition from purely electromechanical telephony to electronically assisted office communications. Designed for executive offices, conference rooms and similar environments, it predates the modern speakerphone by many years and demonstrates the level of engineering that the General Post Office invested in business telecommunications during the period.
Examples appear only infrequently on the open market, particularly in such complete cosmetic condition. Whether you intend to restore it, preserve it as a museum-quality exhibit, display it as part of a telecommunications collection or use it as a period prop for television, film or theatre, it is a fascinating survivor from the GPO era.
Related Equipment
I regularly acquire unusual scientific, photographic and communications equipment including GPO and BT telephones, telecommunications apparatus, cameras, lenses, darkroom equipment, enlargers, projectors, optical instruments, laboratory equipment, test gear, vintage electronics, radio equipment, valves, engineering instruments and other specialist technical items. Please see my other listings if these subjects are of interest.