The basic Großer Feldklappenschrank consisted of metal stand with folding legs. The stand was wide enough to support two base units known a Untersatz. There were four types of Untersatz: A, B, C, and D. Untersatz A was the most common and was set up for ZB/OB (Zentralbatterie Betrieb/Ortsbatterie Betrieb) operation. It was set up to handle up to 10 ZB/OB calls. Untersatz B had a metal desk top. Untersatz C and D were similar to the Untersatz A, but were used to set up SB (Schlusszeichen Betrieb) telephone exchanges. SB exchanges were abandoned by the Wehrmacht mid war. Modular boxes could be stacked on the base units. These boxes included answering boxes, rotary dial amtszusatz boxes, and conference call boxes.
Check out my new book on WW2 German field telephone equipment…
WW2 German Field Telephone Equipment 