Ed Schmidt asked, "How do you change the drive belt on a 20-note
Hofbauer Organ?"

If you have a Hofbauer 20, you will find some useful information at

http://www.wallace-venable.name/mechanical-music/Hofbauer-20/index.html 

It deals with multiple aspects of these nice instruments.  As I recall,
I have replaced a drive belt on someone else's organ, but I've forgotten
the details.  I think you have to disconnect something to slide the
belt off and on.  It wasn't hard, but it took some exploring.

Wallace Venable