Most strange looking gear. Possibly a pre-amp, but there are no other connections visible - certainly is old. Are there any other connections on the opposite end?
With all the advances in electronics, this whole chassis is probably the size of a paperclip today, and not worth much to the common market. Can't find anything on this unit during an internet search.
Gedrückt translates to "depressed" - Must be if one presses down on that knob, it adjusts the mono channel.
Netz tranlsates to "network" and ein is "one". kontrolle is "control".
What kind of electrical connection does it have?