[ Ref. 170207 MMDigest, Extra Holes in Ampico B Tracker Bar ]

I'm pretty sure the long grooves that have the extra holes, both
above and below the line of normal tracker bar holes, are for the
purpose of reducing drag on the paper as it passes over the tracker
bar.  The full height of the tracker bar is still there to support
the paper, but by having those grooves and the vent holes the paper
is not sucked down to the face of the tracker bar with as much force.

I first saw this on a Hupfeld DEA tracker bar and then again on a Welte
Philharmonic organ tracker bar out of a very late vintage (possibly
1930's) roll changer.  This may have been an improvement instituted by
Kimball after they acquired the assets of Welte-Tripp.

Below are links to a couple of photos of the Welte organ tracker bar
with the milled out slots that run the full length of the tracker bar
both above and below the note holes.  You can clearly see the 10 relief
holes which allow atmosphere into the slots to relieve paper drag
across the bar while still allowing plenty of support to the paper.

Dave Krall
Hammond, Indiana

 [ T150 tracker bar from Welte Philharmonic player pipe organ
 [ http://www.mmdigest.com/Attachments/17/02/13/170213_083800_100_4217.JPG 

 [ Detail, T150 tracker bar
 [ http://www.mmdigest.com/Attachments/17/02/13/170213_083800_100_4219.JPG