There are some quick looks at the construction details for a 37-note
wooden tracker bar in:

  Crank Melodica, House of the Rising Sun
  http://www.youtube.com/watch?v=NyghKG4cZik 

I would guess the spacing is the same as used by Raffin, but no
numerical details are given.  The tracker bar pictures start at about
1 min 15 seconds from the beginning and last about 10 seconds.  There
are a lot of interesting "flash" views of construction details in this
video.

The author, who calls himself FlpBusker on YouTube, has a total of
32 videos on line, nearly all of which appear to relate to small
mechanical instruments.

Wallace Venable

 [ See also http://www.youtube.com/user/FlpBusker  The builder is MMDer
 [ Wagner Mello of Herndon, Virginia.  His MMD articles are indexed at
 [ http://www.mmdigest.com/archives/Authors/Aut4123.html and his busker
 [ organs are described at http://members.cox.net/wmbusker/Busker.shtml 
 [ and http://members.cox.net/wmbusker/Uni26.shtml  -- Robbie