This is a teletype modem and power supply.

Translated from the Merkblatt D 764/5 - Fernschreib~Anschlußgerät - 16.8.39 (courtesy of Remco Caspers)

A. General Information

Device description

  1. For the configuration of the teletype-modem, follow the instructions in this document; install the device in the specified position, and become familiar with the controls.

  2. The teletype-modem set is comprised of:
    1. The device case with the contained device,
    2. The lid of the device case with the power cord wrapped around the retaining protrusions. The cable is is 3 X 0,75 mm2 (with the Schuko connector and coupling connector) 5 meters long,
    3. 4 vacuum tubes of the type RL 2 T 2
    4. 2 threaded covers for the Wickmann-fine-fuses with 2 "fine fuses" of the type "Ziff.e".
    5. 10 Wickmann-fine-fuses of 260 mA (in reserve),
    6. 4 telegraphy relays T.rls.43a.


  1. The teletype-modem is suitable for connection to cables for telegraphy or telephony under conditions described below.
    The connection lines may come from:
    1. Field-based wires either suspended overhead or laid underground (light field-cable, heavy field cable, long-distance field cable, telephone cable),
    2. Fixed wire connections (over-head wires of the Postal Service, etc.,).


  1. The teletype-modem features a power supply for connecting to an alternating current voltage of 100 - 220 Volts; current draw is around 0.15 kW including the teletype machine.

  2. The device can be used as follows:
    1. Operating mode: "Ortsteilnehmer" (local participants)
      The device operates as a remote control unit and allows the connection of the teletype machine through a two-wire cable to a teletype exchange switch-board or a converter unit.
    2. Operating mode: "Fernteilnehmer" (remote participant)
      The device operates as a converter from a 4-wire, double-current directly to the teletype machine
    3. Operating mode: "Einfachstrom - Doppelstrom" (single power / redundant (double) power (converter))
      The device operates as with 5b) as a converter from a 4-wire, double-current to a 2-wire, single-current. The teletype is not directly connected to the device, but is connected via a 2-wire line.
    4. Operating mode: "Einton" (single tone)
      The device operates as a connection device to a two-wire telephone line with a tone frequency impulses.
    5. Operating mode: single tone / double-current
      The device operates as a converter from tone frequency operation over telephone lines using four-wire / double-current. The device operates as a converter and can be connected directly to the teletype exchange switch-board or continuously monitored teletype machines like the WT etc.,

B. Operation of the device


  1. Attention !
    The device is open to protect against moisture. The grounding lugs of the device must be connected to a good ground connection before connecting the device to the utility power.
    The unscrewing of the red screws on the front of the device must only be performed by a qualified military mechanic.

    View of the device's front panel (appendix 1, diagram 1)

    1. Open the device by dis-engaging the four buckles on each side of the lid,
    2. Unwind the power cord from inside the lid of the device, and insert the plug into receptacle #12,
    3. Press the red button labeled "Aus" (off) on the switch #15,
    4. Connect the ground wire to the grounding lug.
    5. Connect the other end of the power cable to the utility power outlet,
    6. On the meter #13, watch the reading and set switch #14, until the pointer of the switch points to the correct color area that matches the color of the meter,
    7. Set switch #1 to "Aus" (off),
    8. Press the black button on switch #15 to the "Ein" (on) position.
    9. While watching meter #8, rotate knob #9 "+/- Spannung". The meter must show between +/- 60 and 70 Volts.

Attention !
With the teletype-modem operating in the modes of local participant, remote participant and single-tone, it makes no difference which utility power setting (100 - 220 V) is chosen, in every case connect a teletype machine with a 220v/110v motor.


  1. Operating Mode: local participant "Ortsteilnehmer" (appendix 1, diagram 2)
    1. Rotate switch #10 until it points to the label "Ortsteilnehmer" (local participant).
    2. Connect the teletype machine
      Insert the ZB-connector into socket #3
      Insert the motor connector into socket #11
    3. Rotate knob #5 counterclockwise until it clicks and stops.
    4. Connect the signal line to the"Ortsteilnehmer" (local participant) lugs (a) and (b).
    5. Turn knob #9 to the setting W5 "Ortsteilnehmer".
    6. Move the switch #4 to the position "Anruf" (call), and secure it in that position, then turn knob #5 until the pointer in meter #8 shows 40 mA in the BLUE AREA.
    7. Release the switch button and wait, until the teletype machine is switched on
      In the case that the other side is not switched in, look for a lack of deflection on the #8 meter. Repeat the procedure in 7f) in short intervals, until the other side is connected.

      aa) When connected to a converter with a four-wire line, it works without a switchboard, then the teletype machine is switched on
      immediately after.
      bb) With the connection to telex switch boards, this happens only after the switch board is queried.

    8. Initiate contact with the peer teletype machine, and jointly set the line current to 40 mA. (Resistor #5 should be switched off, on the teletype terminal device and the knob should be turned as far as possible fully clock-wise.) Closing signals are generated by flipping switch #4 to "Schluß" (end) for about 3 seconds.
    9. The disconnection of the teletype is the same here as with the peer, as described in point (g). As mentioned in case (aa) above, the teletype is switched off immediately, and in the case (bb) above, the teletype is disconnected at the switch-board exchange.
    10. Make a call and examine the closing signal several times, and remember that the call switch must be pressed for about 1/2 second, and 3 seconds for the closing signal. With an interference and trouble free call and closing signal, the connection is ready for use.

  2. Operating Mode: Fernteilnehmer (remote participant) (appendix 2, diagram 1)
    1. Turn knob #10 to the position "Fernteilnehmer" (remote participant).
    2. Connect the teletype machines as per 7b).
    3. Rotate knobs 5, 6, 7 to the left until they click-stop as per 7c).
    4. Rotate knob #9 to the setting "Erdprüfung" (ground test).
    5. Attach the connection lines to the lugs: a1, b1, a2, b2. Additionally, these lines are placed one after the other onto the a1 terminal lug. The meter #8 should show from 30 to 70 volts when that line is connected to terminal a1. If the meter does not show any reading, then the connection is broken or the peer is not connected.
    6. Rotate knob #9 to the position "Doppelstrom ankommend" (double-current incoming). The remaining 3 connection lines go to the b1 lug. When that connection line is connected to lug b1, watch the meter #8 for needle deflection.
    7. While watching meter #8, turn knob #6 until 20 mA is achieved (with longer wires, this reading may be as low as 15 mA)
    8. The other two lines are connected to lugs a2 and b2.
    9. Rotate knob #9 to setting "Doppelstrom abgehend" (double-current outgoing).
    10. While watching meter #8, set knob #7 to 20 mA. The unit should be connected in the "off" state for 1 minute, so the testing of the on and off states may begin.
    11. Switch the device on and off - going back and forth (to "pump" the device), so that the wires on connectors a2, b2 are exchanged with each other.
    12. Immediately switch the device on (the teletype should start running) and leave it on for a while, so that the other peer teletype machine can make the first teletype call. If there is no return message, then use switch #4 to send the closing message.
    13. Wait for the connection to a teletype exchange (switch-board) as described in 7bb). After a short time repeat the test and if necessary, as described in 8l) exchange the wires. If "pumping" occurs, then swap the wires back.
    14. Switch toggle #4 to the "Anruf" (call) setting for about 1/2 second, and wait until the teletype machine turns on.
    15. With the peer teletype machine having a telex connection, set the line current to 20 mA. Now turn the knob #6 to the right as much as possible (Clockwise), whereby the peer teletype machine will also set the "abgehenden Strom" (outgoing current) with knob #7 to 20 mA.
    16. Test the closing signal level as was described in 7k).
      The connection is ready for operation when the call and closing signal are trouble-free.

  3. Operating mode: single power / redundant (double) power (converter) (appendix 2, diagram 2)
    1. Set switch #10 to the "Einfachstrom - Doppelstrom" setting.
    2. Connect the teletype machine as described in 7b).
    3. Rotate knobs 5, 6, 7 to the left until they click-stop as described in 7c).
    4. Connect and test as described in 8d) through 8p).
    5. Connect the teletype machine to the device.
    6. Connect wires to lugs 'a' and 'b' (remote control device).
    7. After calling the peer teletype, set the line current with knob #5 to 40mA as described in 7h).
      (Resistor #5 should be engaged as much as possible, with the knob turned left as far as possible.)

  4. Operating mode: Single tone (appendix 3, diagram 1)
    1. Rotate knob #10 to the "Einton" (single tone) setting.
    2. Connect the lines to lugs 'a' and 'b/E' (Eintonleitung - single tone line).
    3. Connect the teletype machine as described in 7b).
    4. Rotate knob #9 to setting "Anodenstrom" (anode current), and set switch #1 to the "Schreiben" (writing) setting.
      Meter #8 shows the anode current, and should slowly arrive at values between 25 and 35 mA. The teletype machine should start running.
    5. Set switch #1 to the "Aus" (off) setting. The teletype machine should turn off.
    6. Set switch #1 to the "Rufen" (call) setting for 3 seconds, and then return it to the "Aus" (off) position.
    7. Wait for the peer teletype to reply to the call, the bell will ring.
      Then immediately:
    8. Set switch #1 to the "Schreiben" (writing) setting. The teletype machine should turn on.
    9. Start communicating with the peer teletype machine.
    10. Close the teletype connection. Set switch #1 to the "Aus" (off) setting.
    11. It is critical to this operating mode that the peer teletype station sends a confirmation of connection to signify they are ready to receive.

  5. Operating mode: Single tone - double-current (appendix 3, diagram 2)
    1. Rotate knob #10 to the setting "Einton" (single tone).
    2. Connect the teletype machine as described in 7b).
    3. Test the single-tone connection, as described in 10a) through 10k).
    4. Rotate knob #10 to the setting "Fernteilnehmer" (remote participant).
    5. Connect and test the double-current connection as described in 8e) through 8i).
    6. Connect the teletype machine to the device.
    7. Rotate knob #10 to the setting "Einton / Doppelstrom" (single tone / double current).
    8. Set switch #1 to the "Rufen" (call) setting, and wait for the confirmation as described in 10g), and then immediately set switch #1 to the "Schreiben" (writing) setting.

    When the tests are passed under items c) and e) above, then problem-free connections can be made, and the complete connection is ready for operation. With the call over the single-tone line, a confirmation must be received (ring of bell), and switch #1 should be set to "Schreiben" (writing). Switch #1 should stay in the "Schreiben" position as long as the two teletype machines are communicating.
    The switch may be set to "Aus" only after determining that the telegram has ended (through events in the connection or through the teletype machine's existing test set).

  6. During a pause in operations and while in operating modes of "Ortsteilnehmer", "Fernteilnehmer", "Einfachstrom / Doppenstrom", "Umsetzer" (converter) and "Einton" (single tone), the utility power (or emergency generator power) can be turned off. From the remote teletype, the call of the switched-off device is performed in the operating modes 5a), b), c) by toggling switch #4 back and fourth between the settings "Anruf" and "Schluß", and for operating modes 5d), e) through 3-second calls with switch #1. On the device with the switched-off utility power, the bell will ring as an indicator of the other side wanting to connect, then the utility power must be switched on in the device.

  7. It is FORBIDDEN
    1. To change settings of the telegraph and radio relays.
    2. to pull the vacuum tubes out of their sockets.
      The replacement of the telegraphy relays and vacuum tubes should only be performed by an authorized telegraphy mechanic.

C. Troubleshooting

  1. Observation during all operating modes
    If the voltage test after item 6i) (knob #9 set to measurement setting "+ Spannung" or " - Spannung") does not deflect meter #8.
    1. Reason
      Switch #15 has been triggered or utility power is absent. Repeat the procedure in 6e)..h)
    2. Reason
      The fuses Si1, or Si2 (260 mA) are blown (this is indicated by the deflection of the meter by only 8-10 Volts).
      Replace the fuses.

  2. Observation during operating mode: "Einfachstrom / Doppelstrom"
    The signal lines 'a', 'b' are connected to lugs 'a','b' (remote control device). The other (peer) teletype calls, and it solidly registers on meter #8 as 40 mA, when the measurement switch is set to "Ortsteilnehmer".
    Voltage test after 6i) gives good results.
    To determine if there is a possible break in the connection, disconnect the wires from terminal lugs 'a' and 'b', then short the terminals (previously the #5 knob was rotated to the left until it stopped). The meter must deflect to from 30 to 40 mA. The meter should show the line current during this test, otherwise the line has been interrupted or broken.

  3. Observation during operating modes: "Fernteilnehmer", "Einfachstrom / Doppelstrom", "Einton / Doppelstrom"
    The communication lines are connected to the terminal lugs a1, b1, a2, b2.
    The meter registers no signal in the "Doppenstrom ankommend" and the "Doppelstrom abgebend" settings.
    To determine whether there is an interruption in the connection lines, connect terminal lugs a1 with a2, and b1 with b2 (previously the knobs #6 and #7 had to be turned left until they stopped).
    Meter #8 must show a deflection of 10...15 mA in both measurement settings.
    The meter should show the line current during this test, otherwise the line has been interrupted or broken.

  4. Observation during operating mode: "Einton", "Einton / Doppelstrom"
    Switch #1 is pressed down (as described in 10d)).
    While set to measurement setting "Anodenstrom", meter #8 does not show a current reading (does not deflect).
    One of the two output vacuum tubes has a destroyed filament or is otherwise not working.
    After establishing this problem, switch the tubes around (signal tube, or buzzer tube in place of the final tubes). Replace the damaged tube with a new one.

  5. Observation during operating mode: "Einton", "Einton / Doppelstrom"
    The peer teletype sends a tone-frequency signal over the wires, but it does not arrive.
    In parallel to the lines on the terminal lugs 'a', 'b/E' (single tone line) connect high-impedence headphones and listen for the telegraph impulse sounds. If you do not hear tone frequency impulses, probably the buzzer vacuum tube is destroyed and needs to be replaced.
    If these problems are established on this device, then they are to be corrected and replaced with a new one.

    Berlin, August 16th, 1939

    Commander and Chief of the Army
    Army Weapons Office
    Office Group for Development and Testing

Appendix 1 (courtesy of Remco Caspers)



Appendix 2 (courtesy of Remco Caspers)



Appendix 3 (courtesy of Remco Caspers)


This is a teletype modem and power supply.



The lid closed. Fatigue paint. "L41006 / 231"
Fliegerhorst Kommandatur



Cover off. This is a very large device.



Utility power voltage selector.



Utility power socket and output for the teletype motor.



AC utility power voltage indicator. Fuses are to the left.



Spare fuse containers and grounding lug on the right.



Telephone line connection block.



Manufacture data.



Transmit / receive selector.



Teletype connection terminal.



Signal current indicator.



Operating mode instructions.



Operating mode instructions.



Mode switching controls.



Mode switching controls.



Mode switching controls.