Did you acquire that MI-75, Autre?
I'm in the process of restoring one now but I haven't been able to find much information online. I had assumed it would be just a repackaging of an MC-75, but during my visual inspection prior to applying power, I discovered that the output transformer is different, having an isolated winding for the 70, 115, and 230 volt outputs instead of using the one between the cathodes of the 6550s. There's also a socket for an input transformer and, though it won't be very difficult to trace out the connections, I have no idea what model of transformer was intended to be used. Have you been able to obtain a schematic for the MI-75?