GERMAN SPY RECEIVER ??? "PROTOTYPE"

I found two very interesting small receivers. I buyed them from a young guy. Him told me that his grandfather working in german military radio reserch laboratory and during the 50' years realised these two prototype N.1 and N.2 (marked inside) for a special project. The two companion transmitter destructed some years ago for take spare parts. As you can see from the photos the quality of manifacture is high and I really no belive that is possible to realise it home-made. In side two battery place are present. The first one receive two 1,5v battery for the filament The second one receive the 45v or 90v ??? battery for anode