A G harp is definitely the instrument for most Irish tunes in Aminor(ditto a D harp for an Eminor tune). Most Irish and English tunes use F#, not F natural, in Aminor tunes, so the G instrument has all the right notes. And for thickening up your sound with a bit of harmony, the way the notes lie are perfect too. The implied harmonies in the tunes tend to revolve round Aminor and G chords, and youve got the GBD on the blow for your G chord, and ACE on the suck for your Aminor. A doddle!