Hi,
My suspect reiterating drum beater from the PPCo. turns out be in
perfect working order.  Craig Brougher advised me to clamp it solidly
and try it, which I did and it worked perfectly.  I was trying it while
I held it.

Also the design (as I have now found out) is quite a common one used in
many original instruments, and, as Don Teach pointed out, there is a
diagram in Larry Givens book.
Thanks everyone for your help.

Peter Coggins