Conn 90G Valve Trombone
Date: 1970. Previously owned by David Oliver
Strictly speaking this model is borderline appropriate for this website. I restrict myself to Elkhart-Conn (through 1970), which is not quite the same as when Crowell Collier MacMillan bought Conn (in 1969). Either way, this is an unusual model so here it is: an upright valve trombone. It is similar to a model produced by the King company, which King calls the "Trombonium". It has a #4½ bore (0.547"). The 90G was produced between around 1970 and at least 1974. I gather that the 90G's bell section is that of an 8H pasted on to a euphonium valve section.
Apparently the 90G was first developed for use by the Ohio State University Marching Band, who wanted something with a larger bore than the King Trombonium. OSUMB purchased 90G's around 1970. With a bore size, as Conn said, smaller than a baritone horn, it might not have been very different from a Tenor Horn from the 1900's-1920's (see Tenor Horn model 4F for example).
What Conn said in 1974:
Specifically developed for the marching band, combining big trombone sound with easy handling. Same fingering as valve trombone, euphonium, and baritone horn. Same bell as the famous Conn 88H, but the 90G produces a different tone than bass trombone. Valve and tubing arrangement provides bigger bore than average trombone, though smaller than baritone horn. Extra heavy bracing; specially designed tuning slide. Lustre-Conn finish over nickel silver. Cylindrical bore 0.547". Bell diameter 8½". Length 26½".