Date: 1960-Current (2002). Owner unknown
The 36K is a fiberglass sousaphone. These days most sousaphones are fiberglass, but in the mid 1960's when the fiberglass sousaphone was new they were quite unusual. From what I can tell, the Conn 36K might even be the very first fiberglass sousaphone model anywhere. The 36K has a 24" bell and regular action valves (the 22K has a 26" bell and short action valves). Production of the 36K started in late 1960 when Conn sent several instrument around the U.S. during the 1960 football season to evaluate how a sousaphone with a (lightweight) fiberglass bell would be received. It was received very well, as it turns out. Production of the 36K continues to this day.
What Conn said in 1966:
Featherweight sousaphone that even the smallest student can handle with ease. (Weighs only 16 3/4 pounds instead of usual 23 to 30 pounds). Special ABS Polymer detachable bell and fiberglass body are completely dentproof and scratch resistant. Covered by 5-year guarantee. Rich tone quality-darker, centered, easier to produce. Lustre-Conn finish on all brass parts. Bell size: 24".