When I cobbled together my home-made Pianocorder key-top player,
I just happened to luck out that 1" piano jack springs worked quite
well, for fit and application, as solenoid slug return springs for my
unit.  I now notice that some of the springs are not up to holding the
slugs up completely, therefore,  are not doing much in the way of
assisting returning the slug after each strike, either.  Probably most
of the return action is being supplied by the key top.

I would like to tune up my unit and install similar springs, but of
a higher compressive resistance, as I think I can improve fast
repetitions by using a somewhat stiffer spring.  From looking in the
piano supply catalogue, it would appear that jack-springs are all of
a standard stiffness.

No doubt one of you guys will know where I might obtain springs of a
similar size but with a higher compressive resistance that standard
jack springs.

More info: the slug in question weighs about 3/4 oz., travels only
3/8".  At rest the spring is compressed to 3/4".  It requires about
3 ounces force to compress the current spring an additional 3/8".
Just guessing, I figure I should try a spring about twice as strong.
Any ideas on that subject?

Thanks for the help!

Tom Lear
San Francisco, CA