I practice with 3 different Euphoniums, a brass-instrument like a small tuba. One of them - a Yamaha training instrument with 4 valves in a row - has a bad intonation at the natural fifth (upper G) actually the f ... which can hardly be compensated by lip tension or embouchure. I have no idea what could be the reason of this phenomenon as this tone is part of the overtone serie.

I practice with 3 different Euphoniums, a brass-instrument like a small tuba. One of them - a Yamaha training instrument with 4 valves in a row - has a bad intonation at the natural fifth (upper G) actually the f ... which can hardly be compensated by lip tension or embouchure. I have no idea what could be the reason of this phenomenon as this tone is part of the overtone series.