UK Teleprinter's

Teleprinter Machines

A teleprinter of the cold war era was a large Electro-mechanical device resembling an electric typewriter. There was a large public network of machines in the UK, which due to their high cost was almost exclusively for business use. The UK public network was dial up in a similar way to the telephone network, but the two networks were not connected. Some large companies had the own independent network, which more than likely used Post Office private circuits. The Post Office Telegrams division had its own 'TASS' private network up until the 1970's, used for sending public telegrams. This used Creed 11 machines that printed on a thin strip of gummed paper for sticking onto the telegram document.

Before the FAX machine became popular with businesses during the late 1980's, Teleprinters were favoured as an 'instant' communications medium as they produced a hard copy. The data rate, which was considered fast at the time, was 50 baud, with a 5-bit code plus start and stop bits. The signalling was by sending 80 Volts Positive and 80 Volts Negative along the two wires. A good typist could type faster than the machine could send the characters, to prevent this happening the keyboard was mechanically locked to prevent a second key being pressed until the previous character had been sent.

The original Creed 7B below used by the Post Office had no paper tape facilities. Separate tape perforators and tape readers were required. The large box under the desk but normally located in a more convenient place is the power unit providing the 80 volts DC signalling.

The design of the teleprinter is ingenious, consisting of hundreds of moving parts. This was the mechanical equivalent of the UART found in computer modems and decoded the 5-bit code and printed the character on the paper. Only capital letters, numbers and a limited number of special symbols were available. The electric drive motor and speed governor (the black a white round box) which powered both the printing mechanism and keyboard can be seen at the front left. This version is the 7E which included a tape perforator (7ERP).

The old noisy No7 printers were replaced by the Creed 444 machine for business use. The new machines had a built in paper tape perforator and reader. They were much easier to use as the machine could store keystrokes. Later on screen based telex machines were introduced, but the 444 gave good service until the closure of the telex network.

Civil Defence and Military Networks

The UKWMO had its own teleprinter network linking all the ROC Group Headquarters. The Regional Government Headquarters (RGHQ) had a similar network. These operated as Torn Tape Relay centres, which were manual rather than automatic. These are described in another topic. There were links from each ROC Group HQ to its own RGHQ for exchanging detonation and fallout information. In Northamptonshire, the Council civil defence bunker at the Henley Centre had a point to point teleprinter link to the bunker in the Town Hall at Northampton.

In the UK there was a military teleprinter network known a the DTN (Defence Teleprinter Network), again maintained by Post Office Telecomms. I never had the opportunity to work on the system, so I have no idea on whether it was an automatic network or a Torn Tape Relay system. The DTN was decommissioned many years ago.

Photo's courtesy of the Radar Museum, Neatishead.