Date: 1926. Owned by Dave Nickerson
The 20I and 50I are two versions of the same instrument; the 20I has short action valves and the 50I has regular action valves. The 50I was produced between at least 1924 and 1950.
What Conn said in 1931:
This is a popular model, being the least expensive of the Wonderphone type of euphoniums. The bell-front type of bell is detachable and can be adjusted to throw the sound outward into any desired direction. It possesses a big, beautiful baritone quality of tone and due to its glassy smooth inside surface produced by the Hydraulic Expansion Process, it is extremely easy to blow. The mouthpipe which enters directly into the valves is only one instance of the scientifically correct design which makes this euphonium accurate in intonation and smooth in scale. Equipped with the famous Conn light action valves.