The Festungs Tischfernsprecher 39 (Fortress Desk Telephone 39) is very similar to the Tischfernsprecher 38, but, there are differences. The Festungs Tischfernsprecher 39 has a handset like a civilian telephone without a talk button in the handle. There is also a rubberized cord on the handset. The handset cord is wired into the telephone’s termination board… Not connected with a plug. And most obviously, there is no battery/terminal box (Beikasten)..
Since there is no battery/termination box, the Festungs Tischfernsprecher 39 must be directly connected to telephone lines (La and Lb), a battery, and an optional auxiliary bell (Wechselstromzusatzwecker). The batteries a kept in a wall mounted battery box.
The Festungs Tischfernsprecher 39 microphone circuit operates on a higher voltage than a typical field telephone. How high? Well there is some confusion. A 1940 handbook states that the Festungs Tischfernsprecher 39 is powered by two T30 cells connected in series (3 volts). However, my friend Albert Lampl has a Festungs Tischfernsprecher 39 pictured on his website with a termination board that is labelled with a 4.5 volt battery supply (MB).
For more information about WW2 German field telephones, check out my book: https://www.lulu.com/en/us/shop/rotwang-manteuffel/world-war-2-german-field-telephone-equipment-a-basic-guide-for-reenactors-and-historians/paperback/product-976w9q.html?page=1&pageSize=4
WW2 German Field Telephone Equipment 