This has adjustable clockspring tensioners, like on my Alex. Probably from around the turn of the 20th century.
Principal tuba, Bel Air Community Band
Old (early 1900s?) Alexander BBb proto-163
1976 Sonora (B&S 101) 4-rotor BBb
1964 Conn 20J/21J BBb (one body, both bells)
1970s Marzan Slant-rotor BBb
~1904 York 3P BBb Helicon
Old Alex Comp.F, in shop