It's a bear!

LLM Self-Balancing with F-attachment
Bore: .485"-.500" (12.3 mm-12.7 mm) (not original)
Bell: 7½" (190.5 mm)

This horn has done some travelling. I purchased if from a Trombone Forum member in Sweden, but the label in the case is from a store in Berlin, Germany. The throat on the bell is very large in comparison to the flare (a cup mute that's properly sized for a 7½" Super bell just rattles around). The inner slide tubes are not original (they have soldered-on stockings), so it is possible that the orginal tubes were larger (in Olds horns of this vintage, the same outer slide will fit a .485"/.500" inner or a .495"/.510 inner). The serial number is in the 8100 range, placing prodcution sometime in the mid-1930's. If the f-attachment tubing looks large, that's because it is - .565". With the .485"/.500" slide, the low range is a struggle; swapping in a .495"/.510" slide opens things up significantly (I tried it with a .525" slide from a Bach 36 and it's a whole different horn). Like later Olds small-bore f-attachment horns, there is a "dogleg" between the tenon joint and the valve to allow more clearance between the player's neck and the valve and neckpipe, but on this horn, the offset is diagonal, rather than being entirely in the plane of the bell seciton.

The case label itself presents an interesting question. A Google search for "Bernhard Mützelberg" turns up quite a few hits listing Herr Mützelburg as a trombonist on some 1920's-era German jazz recordings. It's probably not his personal horn, but it might well have been purchased with his guidance.

Overall view	Engraving	End Crook	Back Side View
	Valve	"Dogleg"
Bell Section in Case		Bernhard Mützelburg Größtes Spezialgeschäft für Jazz - Instrument (Largest Specialty Store for Jazz Instruments) Berlin W. 62. Kleiststraße