Click for homepage
Teletypewriter machines - under construction

This part of the Crypto Museum website deals with automatic (analogue or digital) telegraphy by means of typewriter-style devices, using a binary code such as the common 5-bit Baudot code, or the 7/8-bit ASCII standard. Such systems are generally known as Teletype machines (after the Teletype brand), Teleprinters, Telex (short for Teleprinter Exchange), Tele-Typewriter or by its abbreviation TTY. On these pages we will use the generic name Telex to identify these systems.

Telex machines are operated over land lines (TTY) or via radio (RTTY), mainly using the standard speed of 45.45 baud (USA) or 50 baud (Europe). The use over radio links is also known as Telex Over Radio (TOR). Punched paper tape was commonly used with telex equipment for storing and (re)transmitting messages. Although telex has been superceeded by modern computers, some computer terminal sessions are still called TTY, for example on UNIX-like operating systems.

Although Telex machines are not cryptographic devices, many of them were used in combination with external cipher machines and some even had built-in cryptographic capabilities. For that reason, some telex machines are described on this website. For a more exhaustive overview of telex machines, please check out the Telex Museum of Henning Treumann in Germany [1].

Telex equipment on this website
Hellschreiber, Feld-Hell and other HELL-based systems
Gretag ETK-47 teleprinter with 14-bit technology
RFT ATF Hellschreiber
Siemens T.send.61b punched paper tape transmitter
Siemens T.send.77 double punched paper tape reader
Siemens T-68D telex machine
TeKaDe FS-200Z military electronic teleprinter (telex)
Santec (Helioprint) GNT-4606 paper-tape puncher/reader for telex and computer
Facit N-4000 paper tape reader/puncher
Siemens T.lab.340a teleprinter speed error recorder
MITE UGC-41 teletypewriter (US Navy)
AEG Telefunken Telestar 120, 121 and 122
Random number generator for the creation of key tapes
Repair and maintenance tools
Telex manufacturers on this website
Creed Teleprinters
Gretag ETK-47 teleprinter with 14-bit technology
Rudolf Hell
MITE Corporation
Siemens & Halske
AEG Telefunken
Teletype Corporation
For many years, Telex was the de-facto standard for communication with the Armies world-wide. It was introduced long before WWII (in 1849) and lasted until the 1990s. It was also used by press agencies, governments, large corporations and by the police. Telex can be employed reliably over (fixed) land lines as well as over radio (HF). In the past, most countries had their own Telex network, consisting of decicated land lines and special exchanges, but towards the 2000s most of them were gradually phased out. Today, Telex is still used by radio amateurs (HAMs).

Although most telex systems use the 5-bit digital ITA2 code, generally known the Baudot code, there are systems that use a less-common standards, such as the multi-tone COQUELET code, often used in France, and the 14-bit ETK standard that was introduced by Gretag in the 1950s. Such systems were considered more fault-tolerant but never met wide-spread acceptance.

Telex today
Telex — short for Teleprinter Exchange — is a world-wide communications system of the past. It was once one of the most important methods of communication between companies, embassies, governmental bodies, public services, etc., but lost its popularity in the 1980s, when they were gradually replaced by fax machines (which have now been superseded by modern computers).

Nevertheless, they are marvels of electrical and mechanical engineering, and many collectors and museums make an effort to preserve them for the future and keep them running if possible. This can be done via wire (TTY) or via radio (RTTY). There are several initiatives that allow (private) collectors and museums to take part in a modern world-wide network of teleprinters, such as TelePhone and i-Telex listed below, with the latter being the most future-proof system.

In order to keep old Teleprinters running and to be able to demonstrate the surviving machines, a group of enthusiasts has setup the so-called TelexPhone project [2]. It allows telex machines to be connected to a hobbyist telex network using standard (analogue) telephone lines (POTS).

A customized modem (TxP) has been developed to convert the special Telex signals into standard modem data, allowing any standard telex machine to be connected to another telex anywhere in the world, without any modifications to the equipment at either side. This project has meanwhile evolved into TelexPhone 2, also known as i-Telex, for connection via the internet (see below).

As analogue telephone lines are gradually disappearing, and telecom providers are discouraging the use of such lines, the above TelexPhone idea has been ported to the internet. By using a simple interface, it is now possible to run teleprinters on a world-wide virtual telex network [6].

 More about i-Telex (off-site)

Telex machines were developed and produced world-wide by a variety of manufacturers. Most of these machines were compatible in one way or another. The initial machines worked at the rather low baud-rate of 45.45 baud or 50 baud, but later machines were capable of running at 75, 100 and even speeds up to 150 baud as well. The following manufacturers produced telex equipment:

  • ACEC
  • Creed
  • Gretag
  • Hasler
  • Lorenz (SEL)
  • Olivetti
  • OKI
  • Philips
Alternative devices, which resemble a teleprinter but do not follow the Baudot/ITA-2 standard, were developed by:

  • Teletypewriter
  • Teleprinter
  • Teletype
  • TTY (TeleType)
  • RTTY (Radio TeleType)
  • Telex (Teleprinter Exchange)
  • Fernschreiber (German)
  • Verreschrijver (Dutch)
When bringing old teleprinter equipment back to life, it may be useful to know how existing telephone connectors were wired at the time for use in combination with telex equipment. Note that the wiring of a telex machine can be very different from a standard telephone set and that many different configurations are possible. Also note that a current-loop system is used.

6-pin circular plug
One some older teleprinters, in particular in the Netherlands, a large 6-pin circular connector was often used. These connectors were also used on early cipher machines like the Philips Ecolex II and Ecolex IV. In later years, the 6-pin connectors and sockets were often replaced by the circular Walzenstecker (ADoS) or the more popular ADo 8 (see below).

  1. TX relay A (common)
  2. TX relay Z (mark)
  3. TX relay T (space)
  4. 120Ω RX relay (with 6)
  5. Alarm contact (with 5)
  6. Alarm contact (with 4)
  7. 120Ω RX relay (with 3)
The eldest connector used for teleprinters in Europe is the so-called Walzenstecker (wheel plug); a circular plug with four contacts that was originally used for the connection of telephone equipment, wired as (1) a, (2) b, (3) bell and (4) gound, but reused to accomodate the TX and RX contacts of a teleprinter. The pin-out for use incombination with telex equipment is given below.

The official designator for this plug is Anschlußdosenstöpsel ZB 27, or ADoS ZB 27.

ADo 8
The Walzenstecker shown above was later succeeded by the more versatile 8-pin connector known as ADo 8. This connector was used for a variety of equipment and had two 'coded' guide pins at the centre, to ensure that the plug is entered into the socket with the right side up, and to avoid the wrong plug being inserted into the wrong socket. The sockets are 'programmable'.

  1. TX a (a1)
  2. TX b (b1)
  3. RX a (a2)
  4. RX b (b2)
  5. Bridge to 6 1
  6. Bridge to 5 1
  7. -
  8. -
The orientation of two small discs inside the socket can be altered in order to configure it for various applications. The image above shows the correct configuration for use with a teleprinter. Pins 1-4 are used for the same signals as on the earlier Walzenstecker. The bridge between pins 5 and 6 is optional 1 and is used on newer equipment to signal that the teleprinter is connected.

  1. This is a bridge inside the socket (not the plug).

Adapter between ADo 8 and Walzenstecker
The table below shows the wiring for an adapter from ADo-8 to Walzenstecker or vice versa.

Signal ADo 8 1 Walze 2 Colour Description
a1 1 1 (a) white TX a
b1 2 2 (b) brown TX b (no bridge to 3)
a2 3 3 (w2) yellow RX a (no bridge to 2)
b2 4 4 (c) green RX b
  1. Bridge between 5 and 6 in ADo-8 socket only.
  2. Original name when used for telephone shown in brackets.

RTTY   Radio Teletype
TOR   Telex Over Radio
TTY   Teletype
Baud   Bits per second
Common expression for specifying the transmission speed of a digital telegraphic data signal, derived from the Baudot encoding standard, also known as bits-per-second (bps).
  1. DF3OE's Fernschreiber Museum
    Teleprinter museum by Henning Treumann (German/English).

  2. TelexPhone project
    An initiative of Henning and Philipp in Germany.

  3. Fernschreibamt Hausneindorf
    Private teleprinter collection of Michael Brandes (Germany). Retrieved April 2012.

  4. ECMA, Standard ECMA-10 for Data Interchange on Punched Tape
    2nd Edition. July 1970.

  5. Wikipedia, Radioteletype
    Retrieved january 2014.

  6. i-Telex - Telex over Internet
    Retrieved Sepetember 2019.
Further information
Other websites
Any links shown in red are currently unavailable. If you like the information on this website, why not make a donation?
Crypto Museum. Created: Saturday 07 April 2012. Last changed: Monday, 09 January 2023 - 15:23 CET.
Click for homepage