Transitional Style H (and possibly Style J)
Solo Valve System

Transitional solo system used only briefly in 1917.

(Photograph courtesy of Don Teach)

The rare transitional solo system was used only briefly in 1917, judging by the only known example (#74,785). It uses a different valve system with pipe chest pneumatics that are reversed from normal. All the pneumatics must be collapsed to keep their notes from playing, and letting air into a pneumatic allows a small hinge spring to open it and play the note. The valve system remains undocumented at this time.