This is a large 6-valve rotary F tuba made in Germany by B&S.
The bell is stamped 3100W but this tuba has been known as the PT-12 forever, a model number likely devised by Tucci and the former US importer. The bell is also stamped "Perantucci" which is rarely seen on new tubas in the US anymore. (The name "Perantucci" is not owned in the US by the maker.)
This PT-12 is special with its all gold brass tuning bows. I have not seen another like it. The advantage of the 4+2 fingering is that your right hand can relax a bit without the requirement of a busy working right thumb. On this tuba you don't really need to pull slides. The pitch is good and there are plenty of alternate fingerings if needed.
The PT-12 is a great solo horn, also for recitals and auditions. You may find it more challenging in a quintet setting where the tessitura is lower. Recommended mouthpieces: RT-64, RT-65, RT AMH Paul.
In addition to being endorsed and perfected by Robert Tucci, this tuba is also endorsed and played by: