Dear friends, Robbie asked about the 20-note organs:
The scale of the 20 note organs: between the holes the distance middle to
middle of the hole is: 3.857 mm (millimeters). [ This is exactly 7 holes
in 2.7 centimeters. -- Robbie ]
Carl Frei made for some organs 20 notes plus 2 extra holes for the double
bass-pipe and a moving figure. The paper is exactly 11 cm wide. The
normal 26-note music-roll you can't play on this scale.
All the music-rolls which you can get for the 20-note organ with 11-cm
paper you can play on all organs built in Germany. The scale was
published by Carl Frei Senior, and the other factories which came later
used this scale. I hope this will help you.
Wolfgang Brommer, Organ Masterbuilder