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TCD Siemens Circuit diagram →
Teleprinter connection device
- this page is a stub
T-56 is a teleprinter connection device (TCD) —
(German: Fernschreib-Endsatz or Fernschreib-anschlussgerät
(FAG)) — introduced around 1957 by Siemens & Halske in Germany.
It's a universal device for connecting a teleprinter
to a telegraphy dial-up subscriber line (telex), or a
leased line. It is suitable for 2- and 4-wire equipment in
single- and double-current configurations.
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The T-56 is a tabletop device that is housed in a brown or green metal
enclosure. At the front is a sloped control panel with several push-buttons,
a rotary dial and a +/-current meter.
At the rear are connections for the teleprinter, a paper tape reader
and the 2-wire or 4-wire subscriber line.
The T-56 provides the interface between a 4-wire teleprinter and the
2- or 4-wire single- or double-current line. It also provides signalling.
When not online, the device provides line current to the teleprinter and
the (optional) paper tape reader, which can also be connected at the rear.
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It is suitable for fixed as well as mobile use, and was usually
placed aside the teleprinter. It can be used on leased lines,
but was mainly intended for dial-up
subscriber lines, either automatically switched or manually patched.
It converts a 2-wire single-current line to 4-wire double-current for the
teleprinter, but is also suitable for 2-wire double-current (a.k.a.
impuls telegraphy).
Simpler alternatives for the T-56 are the Siemens FAG
and the Lorenz FZGT-564.
For simple single-current configurations
with two machines and without dial-up facility,
Anschlussgerät 13 (connection device 13)
can be used. The latter is ideally suited for 4-wire demonstration setups.
The T-56 was produced from 1957 to at least 1980, with only small differences
between models.
Most versions have German instructions printed
at the bottom of the case, but the versions that came with
instructions in English, are labelled
Telegraph Terminal Repeater T56 (TTR).
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The image below shows the sloped control panel of the T-56.
At the left is a large rotary dial that is used to make outgoing calls
by dialling the subscriber number of the other party. It is a regular dial
that was also used on contemporary telephone sets
like the German W48. To its right is a current meter that can show three
different currents, depending on the setting of the meter function selector
below it. During normal operation it should be in the rightmost position (Fs).
The device does not have a power switch and is active as long as it is connected
to the mains.
At the right edge of the control panel are three adjustment screws that will
be explained later.
At the bottom are five push-buttons with coloured caps, some of
which have an indicator lamp. The rightmost button (Lin/Loc) is an
on/off switch. The push-buttons have the following functions:
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Lamp
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German
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English
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Description
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AT
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✔
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Anruftaste
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Call button
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Initiate outgoing call
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ST
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✔
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Schlußtaste
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End button
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Terminate the current call
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Fs
Lin
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Fernschreiber Linie
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Teleprinter line
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Connect teleprinter to the line
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Fs
Loc
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✔
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Fernschreiber Lokal
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Teleprinter local
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Use teleprinter locally (off-line)
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Ls
Lin/Loc
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✔
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Lochstreifen
Linie/Lokal
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Tape reader
line/local
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Connect tape reader to the line
or use it locally
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All connections are at the rear. A fixed cable is connected
to the mains wall socket. There are ADoS sockets
are for connection of the teleprinter (Fs) and the tape reader (Ls), as well as power sockets
for providing mains power to these devices. At the top left are screw terminals
for connection of the RX-line (a1, b1). Likewise the TX-line is
connected to the screw terminals at the top right (a2, b2).
With 2-wire line configurations, only the leftmost terminal is used (a1, b1).
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Several versions of the T-56 have surfaced,
predominantly with small differences.
The following versions are currently known, based on the observations
of German collector Heinz Blumberg [1] with additional observations from
ourselves, based on the date code of the capacitors.
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5074/14-IX 1959-10 1 5074/14-X 1959-02 5074/14-XIII 1962-11 5074/14-XII 1963-06 5074/14-XV 1967 5074/14 1969-02
5074/14a-IV 1966-01 2 English
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Date stamp at the bottom of the device.
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Based on the date code on capacitor C10a.
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The device is suitable for three different configurations, or modes,
that can be selected with the hidden
MODE-switch at the left side of the device.
This selector can be accessed after removing the cover from the device,
although some models have a
rectangular hole in the left side panel
through with the selector can be accessed.
The MODE-selector is shown in the image below.
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It is mounted on a small sub-frame and has three positions that are
labelled as follows:
- 2-wire double-current
2 Dr
- 4-wire double-current
4 Dr
- 2-wire single-current
2 Dr
The MODE-selector allows two functional blocks of the T-56 to be
bypassed: (1) the single-current to double-current converter, and (2)
the 4-wire to 2-wire converter. This is further explained in the
block diagram.
The chapter below deals with each of these configurations.
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The T-56 can be used in a variety of configurations, or modes, for
use on short lines, long lines, leased lines and dial-up subscriber lines.
It can connect the teleprinter to a local or remote teleprinter exchange,
or directly to another teleprinter, which can be hundreds of km away.
In most cases, multiplexers are used somewhere in the path, to allow
multiple connections to be carried by a single (long distance) line.
Below are some examples of possible configurations.
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In this configuration, the MODE-selector
inside the T-56 is set to the middle position: 4-wire double-current.
Two wires are used for the transmission circuit and
another two for the reception circuit. If the distance between the
teleprinter and the exchange is short, these four wires may be carried
directly to the exchange.
In most cases however, the lines of several subscribers will be multiplexed
onto a single long distance line. At the other end, the line is demultiplexed
and the four wires are connected transparently to the exchange, as shown in the
diagram below.
In the same vein it is possible to connect the teleprinter directly to a
remote teleprinter via a fixed or leased line. Like in the configuration above,
the four wires may run directly to the other end, but will in most cases
be multiplexed with other leased lines. This situation is shown here:
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In this configuration, the MODE-selector
inside the T-56 is set to the lower position: 2-wire single-current.
It allows the teleprinter to be connected directly (without multiplexing)
to a local exchange. This mode is suitable for short distances only,
up to several km, and is shown here:
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In this configuration, the MODE-selector
inside the T-56 is set to the upper position: 2-wire double-current.
It is similar to the configuration above (2-wire single-current),
but is suitable for longer distances (up to several hundreds of kilometres),
as the line is balanced. It is also known as impulse telegraphy.
Just before the exchange, the 2-wire line is converted to a 4-wire line.
2-wire double-current configurations are often used as part of a more
complex routed telegraphy connections, that may run over several long and
short distance telegraphy paths, as illustrated in the diagram below.
In this example, the signal first runs over a long distance 2-wire path, is then
coverted to a 4-wire line, and is then multiplexed over another long distance path.
The 2-wire double-current configuration is also extremely useful for
use on long distance leased lines, as illustrated in the diagram below.
It allows two teleprinters, each with a T-56 connection device,
to be linked directly by means of a single wire pair over long distances.
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When building a local telex network, for example for demonstrations or museums,
it is advised to the 2-wire single-current mode. This mode can also be used
for owners of an iTelex interface, when connecting to
other iTelex subscribers in the world. The T-56 is perfectly suitable for this.
➤ More about iTelex
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Below is the block diagram of the T-56. The device consists of three functional
parts (1, 2 and 3) that are further described below. Blocks (2) and (3)
can be bypassed with the MODE-selector.
The teleprinter is connected at the top left, using 4 wires: 2 for the
transmission circuit and 2 for the reception circuit.
Note however, that it is treated as a 2-wire device, as the TX and RX lines
are connected in series immediately when the wires enter the T-56.
This is done to allow the hybrid circuit to do its job.
The optional tape reader (German: Lochstreifensender) is at the bottom left.
Common to all blocks is the internal power supply unit (PSU). It is connected
the the AC mains and provides the voltages for the relays, plus the positive
and negative currents for driving the single- and double-current telegraphy lines.
The three blocks have the following functions:
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- Teleprinter interface
This part forms the interface to the teleprinter and the optional tape reader
(TR), both of which are treated as 2-wire devices (the TX and RX lines of the
teleprinter are connected in series).
It is also responsible for signalling incoming calls and for dialling a
subscriber number. The line is internally expanded to a 4-wire single-current
system, by means of a hybrid circuit. 1
This part of the device is always used, regardless the
configuration, even when the device is switched to local operation.
This section also control the mains power supply to the teleprinter.
In the original (German) manual [C], this block
is known as Fernschaltgerät, abbreviated FG or FSG.
- Current converter
The middle part converts the single-current TX wire pair into a
double-current balanced signal — and vice versa for the RX wire pair —
making it suitable for use on long distance lines.
This part can be bypassed with the MODE-selector.
- 4 to 2-wire hybrid
This part converts the internal 4-wire double-current signal (the TX
and TX pairs) into a combined two-way 2-wire double-current signal,
suitable for long distance communication over a single 2-wire pair,
with full echo cancellation.
This is done by means of a hybrid circuit. 1
In the original German manual [C], the conversion from 4- to 2-wire
is known as Impulstelegrafie (JT).
This part can be bypassed with the MODE-selector.
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A hybrid circuit, also known as a
fork circuit, can combine and split
two individual signals without one seeing the other. This is done
to avoid echos on long haul telecommunications lines. In the T-56,
the hybrids are not easily recognised as they are formed by two
polar relays of which the multiple coils are scattered througout
the circuit. Several sub-circuits contribute to the currents in these
coils.
➤ More on hybrids
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The the interior of the device can be accessed by removing four screws
(marked with a red circle) from the corners of the bottom of the case,
after which the case shell can be lifted off. All electric and electronic
parts are mounted to the bottom panel, including the control panel
and the rear panel with the connections. The annotated images above and below
give an idea of its layout.
The mains transformer is located at the right side, towards the rear.
To its left are 6 function relays marked H1, U, UH, L, C and AZ.
In front of the relays is a bank of power resistors that are neatly
grouped together. The two
special polar relays (A and B) are located
just in front of the centre. They have a transparent cover and should
not be opened. An extra relay (H2) is located to the left of the
polar relays, and a further relay (D) in the rear right corner.
The complex multi-deck 3-position MODE-selector is located at the
front left, just behind the control panel.
A remarkable feature of the device are the two light bulbs, that are
located to the right of the polar relays. They are part of the
internal PSU and act as a current limiter for the +60V
and -60V rails. They are used as a PTC resistor and
can be seen as an early form of resettable fuse.
Note the hidden toggle switch
that is mounted in a vertical panel,
just behind the current meter. It acts as a shorting bridge and allows
selection between manually patched operation (HV) and automatically
switched operation (TW, Telex). It is shown here in the HV position.
➤ Detailed explanation of the circuit diagram
➤ Detailed explanation of the (hidden) hybrid circuit
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We have collected a number of hints, tips and guidelines that can be
useful when reparing, restoring or adjusting a T-56 unit. These are
based on the collected experiences of German collector Heinz Blumberg,
complemented by our own experiences and observations.
➤ Fault finding and adjustments
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Device Teleprinter connection device (TCD) Purpose Connection of teleprinter to dial-up telex subscriber line Model T-56 Manufacturer Siemens & Halske Years 1957-1980 Designator Fs Sk 5074/14 Standard TW-39 Wiring 2- and 4-wire Current Single and double Signalling Rotary dial, buzzer (2-wire only) Modes 3 (see below) Power 110, 125, 150, 180, 220V/AC, 50Hz Colour Green, beige Dimensions 350 × 250 × 130 mm Weight 8.5 kg
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5074/14-X 1959-02 5074/14-XIII 1962-11 5074/14-XII 1963-06 5074/14-XV 1967 5074/14 1969-02
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- 2-wire double-current
- 4-wire double-current
- 2-wire single-current
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1 × Telegraph Relay A Trls-63a 1 × Telegraph Relay B Trls-64a 1 × Fuse Si1 0.16C (DIN 41571) 1 × Fuse Si2 T4E (DIN 41571) 2 × Fuse-Lamp SiL1, SiL2 T 25/I 5 × Pilot lamp Fg lp 62e
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- Heinz Blumberg, T-56 and additional information - THANKS !
Museum der Sammlungen. Germany, April 2023 - September 2024.
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© Crypto Museum. Created: Friday 30 August 2024. Last changed: Friday, 13 September 2024 - 15:35 CET.
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