A bit more on the recent discussion about single-ear tracking systems.
Dan Wilson described how the single-ear systems seen in the UK are
fitted with a locking device that prevents any tracking action in
rewind.  This uses a sprung pneumatic, powered from the stack supply so
that the lock is removed during play.  The lock consists of a bar with
a slot that links with a pin in the tracking pneumatic.  When the bar
is in place, the tracking pneumatic cannot move, and the device stays
centred.  (I've sent a photo of the action fitted to my 65/88 note
Pianola pushup, in case anyone sees fit to make an Aeolian-like locking
device for their own machine.)

The interesting thing about this is that the locking device was quite
obviously fitted after the machine had been made.  Aeolian pushups
mostly seem to have a label stuck in front of where the tracker is
fitted that tells owners about a spare linkage to operate sustaining
pedals for grand pianos.  The locking device for the tracker is screwed
on top of this label on all the machines I have seen.  The same modifi-
cation has been made to all the machines, so it's not a home-made fix.

The conclusion must be that either the UK branch of Aeolian decided
to fit an extra locking device to these machines (which were all made
in the USA but labelled for the destination market), or that American
Aeolian changed the machines between manufacture and shipment.

Perhaps this answers the questions expressed earlier in the MMD about
how the single-ear devices must have worked originally, despite the
present-day problems they present.  This modification shows that the
devices were problematic right from the start!

Julian Dyer

 [ See the photo and other articles about tracking systems at 
 [ http://mmd.foxtail.com/Tech/  -- Robbie