Date: 1946. Owner unknown. Picture courtesy David Charrier.
I have learned that the 30I is the same as the 60I except that it has "short action" valves. Production started in 1935 (I was contacted by someone who's father picked up a 30I at the factory in 1935 and was told he had the first one). While I had expected production to end in 1940 or 1941, the instrument pictured here has a serial number dating it to 1946. Presumably production ended in or shortly after 1946, making this one of (or even the) very last ones made.
What Conn said in 1938:
The new 30I Wonderphone euphonium with 5 short action valves is similar to the regular 60I, which has been the choice of such world famous soloists as Simone Mantia, Noble Howard, Jean Manganaro, Joseph DeLuca, P.C. Funaro and Salvatore Florio. Now with the new Conn short action valves, it stands head and shoulders above anything that has ever been built. These marvelous new valves give the soloist a valve action which is actually 4/64 of an inch shorter than that of a cornet. Compared with the old euphonium, this new model cuts the player's work and increases his speed and technique 25%. This new euphonium has made old models obsolete and out of date. This is the instrument for the player who wants to be on top! Has a beautiful, sonorous tone, surprisingly easy response, one of the most accurate and flexible scales ever built into a euphonium, and almost unlimited resources due to the five valves and double bells. The large bell is the principal bell, the small one being used for trombone and echo effects. Both are adjustable and detachable. The fourth valve bridges the gap in the bottom of the scale between low E and pedal Bb, while the fifth valve controls the small bell. Built in Bb.