Hi All,  I recall reading somewhere, many years ago, that the early
Ampico B pianos had a too strong spring in the amplifier and were some
what strident.  Later B pumps had a spring of lower spring constant "k".
A lower spring constant would require a spring of either smaller wire
diameter or, if the wire was the same diameter, a larger coil diameter
would also reduce the spring constant.

A replacement spring should have about the same length but this is not
critical as the system is some what forgiving.  Whatever one does the
minimum intensity may need to be restored by adjusting the stack
adjustable pressure see manual.

The spring constant will be reduced rapidly buy reducing the wire
diameter so a small change in wire diameter will give a large reduction
in spring constant.  The spring constant will be inversely proportional
to the number of coils, i.e., twice the number of coils means the
spring is twice as long and the spring constant will be half that of
the shorter spring.  If the diameter of the coil is doubled for the
same diameter wire and length of spring, then the spring constant
is halved.

Various springs can usually be found in your local hardware store.
I hope this helps,

Allen Ford
Maryland