"Double door wall cases"
(Click at the pictures to see a real version of the phone).

Picture 411, click for a real version, Museum für Post und Telekommunikation
 1881

The first type of a wall telephone, march 1881
- case of oak or walnut with two doors
- 2 Siemens telephones (double pole)
- battery calling
- DC ringer
- local battery working
1881

The second type of a wall telephone, end of 1881
- case of oak or walnut
- 2 Siemens telephones
   (double pole)
- battery calling
- DC ringer
- Lightning arrester
- local battery working
Picture 412, click for a real version, Museum für Post und Telekommunikation
Picture 413
 1886

The 1881 type with
another telephone,
model M.86 (double pole).
Introduced in 1886
1887

The 1881 type with two
telephones M.86,
a carbon-cylinder mikrophon,
invented by Mix&Genest, Berlin,
and an induction coil.
Introduced in 1887
Picture 414
Picture 415
 Batterycase

All these telephones needed local
batteries for calling the exchange
(6 cells) and, if a carbon-microphone
was available, for the microphone
current (2 cells).
These batteries were housed in little
wall cupboards.