The Amtszusatz was a rotary dial attachment for the small, 10-line German field telephone switchboard. It was designed to connect any one of the switchboard’s 10 lines with the ZB (Zentralbatterie Betrieb) automatic telephone exchange on the Reichspost or other telephone systems. These rotary dial ZB systems were supported in civilian telephone service throughout the world into the 21st Century.
Although many civilian telephone systems no longer support rotary dial telephones, you can use your Amtszusatz to make and receive calls through your smartphone with a Bluetooth device known as an XLink. Xtreme Technologies XLink Model BT is Bluetooth gateway that automatically converts rotary dial pulses on the Amtszusatz to touch tone DTMF signals on outgoing calls on a paired smartphone. Incoming calls are passed directly through to the Amtszusatz.
To use my Amtszusatz at reenacting events, I put the XLink in an old ammo box and hide my smartphone in my tunic pocket.
The XLink runs off of a 9VDC wall adapter which is unsuitable for the field. So, I power it off a rechargeable 12VDC lead-acid battery. The power circuit is shown in the diagram below…
The telephone connection to the Amtszusatz is made by running field telephone wires from a modular jack on the XLink to the “Anchlußkklemmen für die Amsleitung” terminals on the Amtszusatz. La connects with the green and Lb connects with the red on the modular jack.
You must use a modular jack with screw terminals that accept regular wire. These are readily available from companies that sell parts for antique telephones.
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WW2 German Field Telephone Equipment 