The name of the manufacturer "Elektro Feinbau List G.m.b.H" could be post-war. During WWII the same company was known as Heinrich List Werke für Elektrotechnik und Mechanik, Berlin.
Teltow is part of "Big Berlin" (after the war in Eastern Germany). In 1945 the factory was taken by the state and given the new name.
I believe the word on the left - bottom is Spannung (Voltage).
Can you post bigger pictures?