Probably the choice of the mouthpiece is not the happiest: size 3 has a very large cup diameter that requires a very developed lip musculature and therefore not suitable for a beginner or a subject who resumes playing after a long pause, moreover the K&G 3C is not a euphonium mouthpiece (all K&G euphonium mouthpieces have the letter D)
2007 Besson Prestige 2052, 3D+ K&G mouthpiece; JP373 baritone, 4B modified K&G mouthpiece; Bach 42GO trombone, T4C K&G mouthpiece; 1973 Besson New Standard 3 compensated valves, 3D+ K&G modified mouthpiece; Wessex French C tuba, 3D+ K&G modified mouthpiece.