I need a little help from the german speaking friends: what's a "Theebrett"?
Of course it's some kind of "percussion", but which one?
Eureka!
I found a note:
"The tea-tray must be of tin, the largest possible, which, like a gong, is struck with the drumstick of a large drum."
That suggests it might be a tuned instrument (like Jamaican steel drums). Maybe different tea-tray sizes give different pitches.
Joe