Hohner Old Standby Harmonica Key of D Hohner Harmonica "Old Standby" These popular beginners harmonicas are also affordably priced Fine construction and tone with heavy plated covers and sturdy boxes Diatonic Harmonicas The reeds of Diatonic Harmonicas produce the notes of the scale to which they are tuned For example, a diatonic harmonica tuned to the key of C would produce the natural notes of the C scale without sharps and flats (picture the white keys on a piano, without the black keys)