Julian Dyer reminded me of the problems I experienced some years ago
(whilst lying on my back under the piano!) of trying to adjust Duo-Art
knife valves without being able to see inside the expression box
bellows themselves.

I solved the problem by gluing transparent sheets of plastic to the
undersides of the two expression bellows instead of the original
bellows cloth coverings.  There are one or two gluing points to watch
when carrying out this modification, but it does make the setting up
of the knife valves much easier.

I later wrote what was intended to be the definitive article on
restoring the Duo-Art grand (British version) which was published in
the Summer 1979 edition of The Music Box.  However pride, or conceit,
comes before a fall, and I made the classic mistake of referring to
suction levels in pounds per square inch instead of inches of water
column differential.  The articles publication was followed by the
sounds of British Duo-Arts imploding all around the country.

David Snelling - Isle of Man