Gerard, I viewed the image of the Chordephon disk, and I recognise the
name of the Waltz, "Unbekend!"There are many old "unknown" songs!   :-)

I think the method of the diazo print will work okay.  I will try this
method myself, using a smaller disk from a friend's collection.  It may
be possible to achieve adequate resolution with a flat-bed scanner,
otherwise I will search for a drum scanner, as is used for color-
separation of large color prints.

Best regards,¶
Robbie