Wednesday, 5 January 2022

GPO 162 pyramid telephone, 1932, Siemens

To ring in the New Year, this week’s blog features one of my favourite objects from MoDiP’s collections: a stunning GPO 162 pyramid telephone. Dated to 1932 and made from compression moulded phenol formaldehyde (bakelite), it sits on a matching Bellset 25 because it did not have an internal bell although, if preferred, the bellset could be wall mounted nearby instead. This example was manufactured by Siemens Brothers (Woolwich).

AIBDC : 008465
Image credit: Katherine Pell

The 162 design appears to be a collaborative effort between the Research Section of the General Post Office and Siemens, when in 1927 the GPO wanted to create a telephone as good as anything then available, but which would not infringe upon existing patents. When released, the Times newspaper noted that the design of the external form closely resembled a set made by the American Telephone & Telegraph Company, but Siemens maintained that one of its engineers had adapted the design from an Edwardian silver ink stand he had recently acquired.

The new GPO microtelephone, without the bellset attached.
Image credit:

The GPO team included A.J.Aldridge, E.J.Barnes and E.Foulger, who conducted extensive experimentation over a number of years to produce a robust instrument ‘of pleasing experience and not easily interfered with by the subscriber’!

For example: the chosen length of the handset was based on the average of measurements taken from a large number of different sized and shaped heads; the 45° angle of the mouthpiece was carefully calculated to prevent the lips from being able to touch it during speaking whilst at the same time maintaining articulation (apparently 90° caused too much discomfort for the user); and the transmitter inset was given a perforated metal guard with the holes set out of line to the holes in the mouthpiece so that there was no possibility for small, foreign objects to be pushed onto the diaphragm.

The mould for the case of a GPO 162 pyramid telephone.
Image credit:

Drop and user tests were completed to check on the performance of the design, the componentry and the materials, with the first model being released in 1929. It was the UK's first telephone to incorporate both the transmitter and receiver into a single unit and was commonly available in black (phenol formaldehyde/bakelite), Chinese red, jade green and ivory (all urea formaldehyde).

An advert for the Chinese red colour, dated 1934.
Image credit:

Early, and now extremely rare, versions were also introduced in a mottled brown/walnut colourway, a dark green, a mahogany and a gold and silver coloured lacquer coating, all examples made of bakelite. Some sources also cite a blue phone but there seem to be no images to evidence this ever having gone into commercial production. In addition to urea formaldehyde for the lighter colours (introduced in 1933/34), Diakon, an acrylic (polymethyl methacrylate) developed by ICI, was sometimes utilised from 1936 and both materials appeared through successive telephone designs such as the 300 and 700 series until superseded by acrylonitrile butadiene styrene from the early 1960s.

Some of the other colours, left to right: jade green, ivory, walnut, mahogany, dark green and gold.
Image credit:

MoDiP’s example is marked GPO S-32/234 No.162CB, suggesting the phone originally had no dial as it would have been used on a manual exchange where the operator would make the call connection. It would have been converted for use with a dial on an automatic exchange at a later date, possibly through GPO refurbishment. The No.164 handset is marked GPO S-32/234 within an oval shaped recess and is attached via a brown 3 core plaited cloth cord.

The base markings.
Image credit: Katherine Pell

It is a beautiful object and will be featured in our next exhibition, Why Plastics?, on display from March 2022. If you would like to come into the museum and see it before then, contact us and we can also show you some other lovely phones from the collection too.


Katherine Pell
Collections Officer



Aldridge, A.J., Barnes, E.J. and Foulger, E. (1929). A New CB Microtelephone. The Post Office Electrical Engineer’s Journal. Vol. 22. 1929. pp. 185-193 (online). Accessed 31 December 2021.

Emmerson, A. (1986). Old Telephones. Shire Publications Ltd: Bucks.

Cook, P. and Slessor, C. (1998). An Illustrated Guide to Bakelite Collectables. Quantum Books: London.

Holdsworth, I. and Trafford, G. (1998). The Design and Manufacture of the GPO 162 Telephone. Plastiquarian. No. 20. Summer 1998. pp. 8-11

Pearce, C.A.R. (1938). Diakon: a new material for coloured telephones. The Post Office Electrical Engineer’s Journal. Vol. 30. January 1938. pp 292-293 (online). Accessed 31 December 2021.

Pearce, C.A.R. (1938). The New Combined Hand Microtelephone and Bellset. The Post Office Electrical Engineer’s Journal. Vol 31. April 1938. pp 1-4 (online). Accessed 31 December 2021. 

No comments:

Post a Comment