Date: 1950. Owner unknown
The name "Connstellation" is reserved for top of the line models. The 28H Connstellation was built between 1949 and 1951. I read on one of the trombone forums that the 28H is a #2½ (0.484") bore.
What Conn said in 1951:
Big powerful tone from this medium bore Connstellation; sounds as if it could be from a large bore trombone! Here is genuine medium bore effort with truly large bore results. True trombone tone quality. Although tone is powerful, it is also bright and solid, with just the right amount of cutting quality. You'll say it's the finest trombone you've ever heard! "Free blowing" scale. The scale is smooth and even, every tone being of the same strength and quality. No rough spots to cause the player to stumble. Resistance held to a minimum necessary for good control. High range performance. The design of the bore in this model favors the high register. The tone quality is big and fat; especially good are such usually difficult and thin notes as high F and G (above the bass clef). Solid low register. An extra-large bell for this bore size "fattens up" the tone in the low register. Also contributing to this solid low register is a different type of bell connstruction. "Fastest action on any trombone". That's what several competent players say. The slides are extremely light, not only because they are drawn thin but also because they are narrow and streamlined.