This is a large hand made rotary valve F tuba made by Dietrich Kleinehorst at Gronitz in Hamburg, Germany.
The distinguishing features of this FZ-126 tuba are the long arced leadpipe and the fifth rotor at the bottom of the stack. The tuning slide is smaller than the model 127 and the fourth valve loop extends to the front of the horn with a convenient water dump slide. Bore size is tapered through the valves: 19/20/21mm.
Overall this tuba is more centered in both the high and low range with some additional resistance down near the pedal F. Though it looks to be the same bugle as the FZ-127, placing the valves further along in the bugle gives it some compactness of tone and an easy response.
This particular "Lacquer Special" example has the fifth rotor operated by the left hand with a very interesting linkage mechanism down to the rotor. This is German style, and allows your right hand to relax a bit more, at some expense of slide pulling ease. I don't know the exact date of manufacture but it was in stock in Deitrich's shop in May 2017. The rotor casings are made of brass with the rotor knuckles and ferrules being made of nickel. The leadpipe is gold brass. The first slide is fairly loose for easy pulling. The leadpipe goes right over the first slide, so you can hang your left hand down if you need to pull slides. The pitch is quite good on this tuba. You shouldn't need to do much slide pulling at all. The low C can center right in, but you have to know how to blow it. Once you get that it's not snarky at all like older rotary F tubas such as B&S. It's big and centered. Below that all the notes also center right in, with just a bit of resistance on Gb. Best fingering for Ab seems to be 1-3-4.