I came across this tuba, it's a Schenkelaars (Dutch company that doesn't excist anymore).
They made their own tuba's, but also stencils. I believe this is a stencil tuba, but can't really figure out what it would be.
At first I was thinking that it was a B&S (because of the wrapped 4th tubing), now I'm not sure since I can't find identical pictures on the web..
Bell is 45cm,
Bore 19mm.
The Leadpipe is in two pieces
Doesn't look like a B&S 101 stencil. Looks Miraphone-ish, but not wrapped exactly like a 186...........
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
The bell profile, lyre holder above the thumbring, and overall visuals look B&M/Nirschl to me. But some of the old rotary Melton/M-W tubas look similar to that, too. A closer look at the bracing will help with the I.D.
I've been wrong before so I don't wanna say "for sure". But I will cautiously say 'Nirschl BBb'
