I hope that I can shoot a few good pictures of it tomorrow. It has cleaned up nicely. I managed to get the engraved text a bit brighter again with the help of a fine screwdriver and a dirt eraser. And all the bare metal parts are looking a bit more shiny again thanks to fine steel wool. It's not perfect, but for an at least 55 year-old pedal the result is really cool.
Yesterday night a read a bit more about the pedal. In the instruction manual it is called "Tonverzerrer TV 1966/67" and "TV 66/67". So apparently the fuzz pedal was introduced in 1966/67 and therefore the tremolo model "Tr 68" in 1968.
My model seems to be a very, very early unit. I really doubt that the people at Schaller used the user-unfriendly 9V battery with soldered lugs for a long time. Every other old unit that I spotted has a vintage looking battery clip. Someone claims to have a genuine Schaller fuzz from 1967 in this shootout video with a clone that he made. It looks exactly like my model, with the PEGEL (Level) knob right in the middle, aligned with the bypass switch. All the other units have the two knobs more on the right, even in the instruction manual and the old catalogues.
Later models have a different circuit with modern looking transistors (at around 1972), at some point BC237B silicon transistors. This circuit has two Germanium transistors! They are Italian AC192 from TES (Tecnica Elettronica System, still existing today). [EDIT: that is incorrect, the brand was ATES, apparently a sub-group of Siemens]
