<html> Bill, The difference with these springs, as compared to the jack coil spring, is that they act directly between the hammer butt and the jack.  Just as a grand repetition spring holds the hammer up to  allow the jack to reset quickly, these upright springs (when working properly) hold the hammer butt away from the jack to allow it to reset without full key return.  Applying this spreading force only when the key is depressed, and adjusting the spring forces to prevent bobbling, are the secret to all such systems operation.  They do work very well. The reason these have fallen out of favor is the cost.  Not enough people want to buy a really expensive upright piano that performs well.  Most (although not all) people who buy upright pianos are looking for low cost. Don Mannino RPT At 05:25 AM 6/19/2002 -0400, you wrote: <blockquote type=cite class=cite cite>Andrew, I have an 1890's Chickering and Sons 79B upright with the Schwander butt and brass rail with the same secondary jack spring.  The first piano I owned with this spring was a turn-of-the-century Bechstein upright.  This was a very responsive action, although I suspect it wasn't because of the extra spring.   Dolge's book has drawings which have the spring on Schwander and Langer actions of the 19th century.   Mason and Hamlin had their own take on the idea using a leaf spring;  I had a "Screwstringer" with this. Greater minds than mine have expressed skepticism over this spring.  If the idea is to return the jack quickly the coil-type jack spring also found on these actions     does a sufficient job.  Getting the jack back under the hammer butt is one thing;  maintaining some kind of perpetual engagement of the two parts, which the grand repetition comes closest to doing, is not accomplished by this design.  The Fandrich/Trivelas action does this, and I can't see how any of these auxiliary springs function to maintain engagement.  It is interesting, though, that most of these actions with auxiliary jack springs have the Schwander butt spring, a weaker spring which results in a less rapid return of the hammer to rest.  This could keep the hammer/butt assembly engaged with the jack, which may be one reason why these actions seem responsive.  But the extra spring doesn't seem to me to do anything different than the coil spring.  If so, it was sure a lot of trouble for nothing.  Any other thoughts on this spring? Bill Shull, RPT </blockquote></html>