Conn 35H Eb Duo-bore Alto
Date: 1966. Owned by Geoff Batchelor
This is an alto trombone, in Eb (which is customary for alto trombones). "Normal" trombones are in fact tenor trombones and are lower than an alto. Notice that this is a tuning-in-slide trombone. The 35H has a #2½ - #3 bore (0.485" - 0.500") and was built from 1965 to at least 1971, on special order.
What Conn said in 1966:
A bright alto voice, ideal for symphonic work as well as jazz arrangements. Also opens new vistas for school band and full brass choir. Brass bell. Dual bore size .484" and .500". Bell 7". Length 33".