On page 978 of the book, "Encyclopedia of Automatic Musical
Instruments," by Q. David Bowers, there is an illustration of a
"Tracker bar ... and attendant assemblies on an electric piano".
We are currently restoring a Harper Electric Piano that has exactly
that configuration.  I just put a video of it on Player Piano Talk
Facebook group:

https://www.facebook.com/groups/playerpianotalk/permalink/10157894649675831/ 

I am hoping Mr. Bowers might recall where he found that illustration.
It looks a bit like a service manual drawing, a patent specification
sketch or something similar.  Was there anything else in the original
document, I wonder?  Does anyone have any extra information?

Thank you in anticipation!

David Evans - Nickelodeon Museum
Cowichan Bay, British Columbia, Canada V0R 1N1

 [ These illustrations are reproduced in Bowers' "Encyclopedia" and
 [ a trade journal of the period.  -- Robbie
 [ https://www.mmdigest.com/Attachments/20/05/02/200502_033417_Bowers_p978.jpg 
 [ https://www.mmdigest.com/Attachments/20/05/02/200502_033417_Harper_advert.jpg