I have just finished an expression box and was able to find GREAT
replacement springs through Associated Spring.  Here is the info:

  Associated spring main page: http://www.asbg.com/
  Catalog section: http://www.asraymond.com/spec/catalog/

Click on extension spring then go to page 22

  E0500-049-3500
  E0500-055-3500

I have spent hours testing three sets of original springs (and an old
replacement set made out of coiled music wire).  I then set out to find
stock springs that were close to the original specifications.  A number
of other men have helped me and know about these new springs.

We are very excited about them.  None of these men have tested a set.
They have agreed with my numbers and believe these springs are very
close to the original springs.  There is a lot of controversy over how
much difference there should be in the spring rate.  I believe the
weaker Accompaniment spring should be 1/2 the strength of the theme for
grand boxes.  If this is your belief then the springs listed above are
your answer.  If not, then there are other springs of 3.5" length made
out of other wire diameters which can be used to either increase of
decrease the spring difference.

I will be writing an article concerning the restoration on this box.
It is possible to have the zero step settings at 5" and 6" and the 15th
step difference at 13", 14", or 15" suction.  I have done it and have
the test and measurements to prove it!  I'll be posting charts and
other info when the article is finished.  I hope to post a sound clip
of the piano when the box is returned and installed.  I will say that
it's not all in the _springs_ nor is it all in adjusting accordion gaps,
nor is it in making any type of modification from the original.  More
later.

Sam Harris
Greenville, North Carolina
http://www.geocities.com/Heartland/Ranch/9374