I agree. A slightly imprefect taper match would cause buzzing and other problems, such as leakage. Also, the mouthpiece could be bottoming out in the receiver.Kevin Hendrick wrote:It does sound like a shank-to-receiver size mismatch, doesn't it? I think the Kelly tuba 'pieces have standard American tapers, so if your horn has a European-sized receiver, you've probably got about a .005" gap all the way around the taper. . . .
Old-time machinists (of which I am one) would check by applying an extremely thin film of artists' Prussan Blue oil paint to the receiver with a Q-tip and inserting the mouthpiece. Gently rotate the mouthpiece to pick up the Prussian Blue from the receiver. Remove and inspect the mouthpiece. If the tapers are not a prefect match, the mismatch will show in the non-blue areas.
All you need is a tiny tube of Prussian Blue from the art supply store. WARNING: Prussian Blue can be horribly messy.
I used a Kelllyberg recently at an outside TubaChristmas with no buzzing or damping that I could tell. I played the tuba 1 parts on my Willson 3050RZ 5/4 CC, and was satisfied. I got the Kellyberg to avoid numb lips.


