While running errands on Saturday I had to stop by a music store and pick up some strings for Edison's guitar.
The closest decent music store was Rush's, in south Knoxville. Before they moved to this location, they had an interesting brass instrument on display. It was a double bell euphonium, made by the King company.
After I bought the strings I asked where it was because I didn't see it on display. Rob pulled it from the boss's office and displayed it.
The fifth valve would direct the air into the second bell.
Here are some links to more double bell euphonium sites: