I will dig the manuals out for the Model 75 and see if I can make a simple explanation - there is a modified bias spring assembly for the receive electromagnet that needs to be solved.
Double current isn't that difficult - it is RS232 at higher voltage
The big challenge for the machine on Double Current is the lack of FSG - rare in England, so probably unobtainable in Germany. Anyway, I will see what I can find for you.
Regards
Sean
669089 Siemen G - T100S Online 24H (Online again)
299709 Antosh G - Creed 444 - Double Current R + D (0800 - 2100) Should be reachable
459724 NC
I found the Single/Double Current convertion on page 70 of the maintenance manual. There is also a reference to a picture.
But I would be very happy if someone with more experience would take a look at it and help with the change.
As soon as I hear back from Roland about the connectors and the connectors are here, we could perhaps arrange a Saturday when I can sit in front of the machine in the museum and take some photos of the current settings.
If you (or perhaps someone else) could figure out how to connect the machine to a single current FSG in the meantime, that would be very helpful.