Hi John, see if this gives you a visual concept.  The spring should lift
at a slow and steady pace.  An easy flow, as opposed to a jumping motion.
(More like the rise of one's head when you comprehend something saying:
"Oh, I see"; not the jerking motion as when being pushed from behind).

Depress a key and hold it down so that the hammer is caught by the
backcheck ('checked-in'), ease up on your finger enough to release the
hammer from the backcheck (maintaining finger on key).  The hammer should
rise.  Adjust the spring tension to the point where you no longer feel a
'kick' or 'bump' in your finger thru the front of the key (the raise
should not be of such a velocity as to bang the repetition lever into the
drop screw).  Treble notes (above treble staff) could stand slightly
stronger tension to insure repetition on trills.  I need to add: the
height at which the hammers 'check-in' should to be set before the spring
tension is adjusted.

This spring tension (adjusted at this minimal setting) may need to be
checked seasonally as the humidity of summer may require a stronger
spring tension to maintain repetition.  So, repetition springs set in the
summer may be too strong for the drier winter action conditions.  For
this reason you will generally find jumping hammers in the winter.  (Too
strong a tension may cause a double strike if the backcheck leather is
dried out and/or not catching the hammer securely or if the action is
regulated to a close let-off).

But when all is said and done, if a piano has good repetition in summer,
and the hammers do not double- strike, not many people re-adjust.  Only the
most critical pianists can notice the difference, and as for player
pianos -- the mechanism is oblivious to the finer nuances.

Jon Page¶
Harwich Port, Cape Cod, Mass. (jpage@capecod.net)