Hello,
Currently on ebay is a photo album with frankly somewhat variable quality of photos. However what is interesting is tha there is a photo of what appears to be a AEG Z.3, to which the serial B.50 is assigned by the compiler of the photo album. As far as I'm aware the Type of machine serial B.50/13 was not previously known.
https://www.ebay.de/itm/276717560011...Bk9SR-imnt3fZA
Regards,
Clint