I'll have to review my notes on the AK mechanic but the SS is the renowned tube mechanic Stephan Schilling(sometimes seen as Str. Schilling) and he may have been in Suhl( Stephan Schilling, Gothaerstrae 82 closer to WWII) or was back & forth between Suhl & Zella-Mehlis. But he was a staple for the tube effort on the wares of the Zella-Mehlis offerings. The possibility exists that there were a couple of generations.

Cheers,

Raimey
rse