It started out as a beat-up King Duo-Gravis that I got on Ebay. I also purchased a Chinese rotary-valve euphonium. I harvested the euphonium's valve section, sold the case, and put the rest into my closet. I removed the valves from the King, along with the tubing segment that goes from the valve to the tuning slide, and inserted the euphonium valve section in its place. Then I rigged up a string linkage system so that I can play it as a valve trombone OR use the slide.
My original intent was to invent a secondary linkage so that I could ALSO use the 4th valve with my left thumb, the 1st valve with my left index finger, and the second with my left 2nd finger while using the slide with my right hand, but I never finished that part of the project.
I have done some big-band work with this instrument and have also performed the Dvorak New World and Berlioz Roman Carnival with a local orchestra and got away with it. I use the slide for long tones and revert to my tuba fingerings whenever my limited slide technique holds me back.
I am certainly not one tenth of the craftsman that Mr. Oberloh is, but the thing is playable. I am showing it here in the hope that somebody else may decide to make a better one.
-Art, the archtypical "shade-tree tuba mechanic"