WTD: 5.25' DSDD drive & Acorn Master128 keystrip scan/schematic

[Eric Smith]

>   I'm after a 5.25" 80-track (preferably 40/80 switchable) DSDD drive,

Never heard of that, and I can't seen any way it could possibly work.
5.25" drives either have a wide head gap for 48 TPI (35-track or
40-track), or a narrow head gap for 96 TPI (80-track) or 100 TPI
(77 track).  You can't "switch" without replacing the heads.

What you can do is read 35-track or 40-track diskettes in a 96 TPI
drive.  The drive doesn't need anything special for that.  However,
writing to them will not work reliably.

If you need to be able to write 40-track and 80-track diskettes, you
need two drives.

Eric