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 OB (Ortsbatterie Betrieb) lines with a ZB (Zentralbatterie Betrieb) telephone exchange. The ZB system was supported in civilian telephone service, including the North American telephone network, into the 21st Century. The Amtszusatz essentially turns the field telephone switchboard into a Private Branch Exchange (PBX).
The Amtszusatz is connected to the switchboard with two sliding bars. The bars are secured with four thumb screws.
The operator’s field telephone wires are connected to the two “Abfr.” terminals on the Amtszusatz.
The ZB telephone line wires are connected to the “La” and “Lb” terminals on the Amtszusatz.
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WW2 German Field Telephone Equipment 