Watch the Harmonic Minor online guitar lesson by John Stowell from Modern Jazz Improv
In addition to the two harmonic minor keys I'm using here (1/2 step above and whole step below as altered dominant/diminished), the harmonic minor a 4th above is also usable. In the progression I'm using by way of illustration (Fmaj-F#o-Gmi, etc.), the F#o can be interpreted as D7 altered, and I will use the chords/scales/arpeggios of harmonic minor in the keys of Eb, C and G.When playing a diminished chord of the key that you are resolving to, in addition to using the harmonic minor a half step above and and a whole tone below the altered dominant, you can also use the harmonic minor a major 3rd above. This sound outlines a Lydian #9, a triad a half step below with a b9 in the bass or a diminished major 7th (i.e., for Fo-Fmaj7, use F, D or A harmonic minor for the Fo chord).