Conn 7H Symphony Small Bore
Date: 1913 Owned by Richard Naumann
The 7H has #3 bore (0.500"), and was built from at least 1913 but possibly as early as 1913 to sometime around 1928 or 1929.
What Conn said in 1925:
The Symphony Model is exceedingly popular for orchestras, generally being used for first trombone.