The Creed 7B Teleprinter - VMARSmanuals

1 The VMARS Newsletter Issue 31 11 October 2003 The Creed Model 7 Page TeleprinterAlan G Hobbs, G8 GOJ/M3 GOJThe Creed model 7 page Teleprinter , whilst not the firstteleprinter to be produced by Creed & Company Limited is,without doubt, the most well known of their machines, and isconsidered by many to be the Teleprinter that helped the Alliesto win World War 2. Many thousands of model 7 s saw servicewith the Armed Forces, sending vital messages around theworld, and sending top secret messages to and from the codebreaking teams at Bletchley Park in the late 1920 s the Post Office were already successfullyusing an earlier Creed machine, the model 3 tape Teleprinter ,for the Inland Telegraph (Telegram) service.

2 Thoughts werenow turning to the introduction of a person-to-personTeleprinter Exchange (Telex) service, but there were nosuitable machines available. The ideal would have been toplace a standard commercial typewriter at each end of atelegraph wire, and cause them to operate one another. Thiscannot be done, as the keys of typewriter operate thetypebars directly, but on a telegraph machine the operation ofthe keybars must generate telegraph signals and the typebarsmust operate under the control of the receiving would have been possible to use the type basket of one orother of the standard typewriters and to arrange this under thecontrol of the receiving mechanism.

3 But this would haveinvolved the development of a machine of a totally differentcharacter from that already in use by the Post Office, , themodel 3 tape Teleprinter . It was considered best to produce amachine as nearly as possible like the model 3, making onlythose modifications which were necessary, and whichexperience with the model 3 had shown to be desirable. Itwas also required that the machine would print on standardwidth paper, just like a typewriter, and not on the narrow stripof paper used for the Telegram service. Operation was to beat the international signalling speed of 50 Bauds, (an elementperiod of 20mS), and to use the five unit InternationalTelegraph Alphabet number 2 (ITA2).

4 These, then, were theaims which led to the development of the model 7 the model 7 was finally introduced in 1931, it was atruly state-of-the-art Printing was done on paper 8 wide, which wassupplied in rolls 3 diameter, with the rolls beingcarried on the carriage within the The typing was done through an ink ribbon, as on atypewriter, instead of the ink rollers running on thetypehead as used on the model Ball bearings were used on all high speed shafts,and oil cups were provided on all small bearings sothat the machine was capable of at least 100 hourscontinuous operation without Communication could be effected with a machine inan office without a receiving operator being inattendance.

5 This feature, known as the Absentsubscriber service , makes it necessary to provide ameans which will enable the calling subscriber toverify that the correct connection has been this purpose an Answer Back device wasprovided on the machine, which is arranged to sendthe exchange number of the called machine back tothe calling subscriber whenever the callingsubscriber depresses a particular key on A signalling device was provided which could beused for calling the attention of the person in anotheroffice to any urgent message received. It could becaused to ring a bell or light a In order to simplify the manufacture andmaintenance of the machine, it was built in units.

6 Themodel 3 was arranged that portions could be readilyremoved, but it was not designed so that it would bepossible to remove a portion and replace it by aspare without re-adjustment being necessary. Themodel 7 was designed so that this was possible,leading to reduced maintenance costs, and making itpossible to effect field replacements in the shortestpossible The automatic motor starting and stopping devicewas completely re-designed and provided with The general design of the machine was such that itcould readily be adapted for any purpose within therange of start-stop telegraphy. This feature arisesdue to the keyboard unit and paper carriage beingdetachable from the receiving portion of themachine.

7 Two types of paper carriage wereprovided, one suitable for printing on a tape, just likethe model 3, and the other on a roll of its production life of 38 years, over 101,000 model 7 swere produced, in many different versions. The originalversion, the 7A, transmitted a 7 unit character, ( , 1 Startunit, 5 Code units, and 1 Stop units) and had a 7 unitreceive cycle. However, a CCIT (Comite ConsultatifInternationale Telegraphique) recommendation was thatmachines should be capable of correctly receiving andprinting characters when each character is sent out as 7 equalunits. That is, with a stop signal of only one unit, instead of theusual 1 units. A re-design of the receive camshaft and itsdrive mechanism reduced the receive cycle to 6 units, andwith the original 7 unit transmit cycle this machine becamethe famous model 7B.

8 There was also a version with a 7 unittransmit cycle, still with the 6 unit receive cycle, known asthe model 7C. This machine tended to be used only on privatewire networks where the shorter stop element produced aslightly higher throughput of information. This was equivalentto 71 words per minute for the model 7C at 50 Bauds,compared with 66 words per minute for the model 7B at VMARS Newsletter Issue 31 12 October 2003 Later versions of the model 7 were introduced to provide theadditional facilities that were required by the Telex network, orto improve the performance of the basic machine.

9 The firstvariant was the model 7D, which incorporated a relay to signalto the controlling equipment when the driving motor hadreached its governed speed. The next version, the model 7E,incorporated a completely re-designed receiving cam shaftassembly, known as the overlap cam unit. With all earlierversions of the model 7, the received character was notactually printed until the next character was received. Thiswas due to the limited time available with the 6 unitreceiving cycle. The overlap cam unit overcame this limitationby means of three sequentially operated cam shafts. The firstcam shaft included an Orientation device (some times calleda Range Finder ) which allowed the sampling periods of thereceive mechanism to be optimised to the incoming second cam shaft carried out the received charactersampling and processing as before, and the final cam shaftcaused the printing to be carried out whether or not anothercharacter was being of these machines were available with the factory fittedReperforating attachment, designated by /RP after themachine description, , 7E/RP.

10 This attachment allowedthe machine to produce a perforated paper tape of allincoming and outgoing messages or, when used off-line, toproduce perforated tape for subsequent automatictransmission, rather than transmitting direct from the final machine in the model 7 series was given thedesignation of model 54. This machine was introduced in1954 as a deluxe version of the model 7E. It included a newstyle of keyboard, designated the type N keyboard, having amuch lighter touch than the original model 7 keyboard, twocolour printing to differentiate between the sent and receivedtexts, with the whole machine being enclosed in a newlydesigned totally enclosing silencing cover.