He may be a god of the trombone, but most of the time, Charlie Vernon is just another figure in black tie, laboring in obscurity at the back of the Chicago Symphony Orchestra. Yet on this particular night in Orchestra Hall, he stood in front, pumping his fists, waving at the audience and bathing in its adulation. Mr. Vernon, the bass trombonist in the orchestra’s legendary brass section, had just finished playing a tour-de-force concerto written expressly for him. This was its premiere run of concerts. Backstage, scores of students, their teachers and fellow professionals from as far away as...