OK accordionists, here is a question. In an article on substitutions I have been reading, the author makes reference to a well known trick, which is to get (for example) an Am7 chord on the bass, by pressing the Cmajor chord button, and reaching over to the A counterbass over the F next door, thus giving you C,E,G,A. Then there is a strange reference to making 7th chords from diminisheds using the counterbass. The basic idea seems to be that the diminished as it exists on the accordion is only three notes -- in C, C, E, Gb. Somehow this can be turned into a 7th of some key by using the counterbass, but I am too stupid to figure it out. Anyone help?

yours,

Peter T.