Well in a C-scale both the 6th and 13th is an "A" so isn?t it the same thing? By the way; why do you wan?t the 9th in a C13?
C13 = C, E, G, Bb, A
C7add6 = C, E, G, Bb, A
I?ll ask my piano teacher
Wandering kid: The 7 is special since there?s a minor 7 (written just as "7" as in C7) and a major 7 (written "maj7" or just "maj" as in Cmaj7 or Cmaj). Not very logical i think but thats the way it work
