Siemens T36Si

[Funksammler]

I would like to introduce the restoration of a Siemens T36Si teleprinter.

By 1930 the development of teletype technology had developed into viable commercial business and the US Morkrum Kleinschmidt company (later merged into AT&T) produced the state of the art teletype machines. Lorenz aquired a licence to use their technology exclusively in Germany, forcing Siemens to develop a different design.

The Morkrum Kleinschmidt machines use only one clutch release magnet for the transmitter and receiver mechanisms meaning they are mechanically coupled. The pulses from the transmitter reach the receiver almost immediately but the pulses from a remote machine only reach the receiver after a short delay which increases with the length of the transmission line. If the transmitters and receivers from both machines are electrically connected to the same line there comes a point that the two machines can no longer synchronise due to the delay. To avoid this problem long teleype connections use four wires, two wires for messages from A to B; another pair for message from B to A (it also means that the machine no longer prints its own messages).

In the Siemens machine the transmitter and receiver are mechanically independent, they both have their own clutch release magnets so in theory the Siemens T36 could be used over a single pair of wires over long distances (as the delay between machines no longer poses limits). So in theory a network based on Siemens machines could be built more cheaply, but since the German Telex network had already developed to be compatible with mechanical machines needing four wire connections, this potential commercial benefit could not be exploited.

Another benefit of the Siemens design is that it is essentially a digital electrical machine; it becomes relatively easy to connect it to peripheral equipment like punch tape readers and writers or indeed cypher units as used in the T52. Each T36 machine has two connection sockets to connect the transmitter to a punch tape reader and the printer to a tape puncher. The use of punch tape allows a message to be pre-recorded on tape and be transmitted at full speed afterwards. Since hand typing could never keep up with the speed of the punch tape transmission times (and with it cost) can be reduced.

Whereas the mechanical machines essentially used a mechanical typewriter as their printer, Siemens decided to go back to the rotating wheel printer first developed in the 1840's. All the characters are placed on a wheel which makes one full rotation every cycle. To print the intended character, a striker pushes the paper against the wheel at the exact time that the character passes by during the rotation. To achieve this, the T36's printer has to convert the 5 bit code into a precise timing moment. Since the wheel rotates in less than 140 ms the striker has to be able to hit with milisecond precision. The resulting printer is a lot more compact and probably cheaper to make than the typewriter type used by the competition but the amount of electrical switching contacts involved make it complicated to adjust and maintain.

Key in the printer mechanism are the five polarized relays that store the five-bit code throughout the printing cycle. The relay coils receiver a short pulse of stored energy from the receiver camshaft contacts and flick the switch contact to the T or Z contact where it stays until the next pulse is received. So in theory the polarized relay can remember the bit information forever. However to achieve the sensitivity and correct balance the relays require regular careful adjustment, one of the weaknesses of the machine.

The attached photographs show the overview of the machine, in later posts I will focus on some of the details

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