First up, my theory knowledge isn't fantastic so please go slow and I don't read music when I'm playing!
I understand the basic major & minor triads, and I use 5th DS quite happily, but I need to understand which chords I can play over a song in a particular key. For example, if I'm playing a song in Gmaj, I know that I'd need to play a minor triad in the second and third positions (A and and major triads in the 4th and 5th (C and D). However, if I want to break away from just playing Double-stops based on triads - and sticking with the example of playing a song in G - could I play a D7 chord in the 5th position instead of just playing a plain old D?
Taking this one step further, is there a general rule that says that I'd always play a 7th chord in the 5th position of any key, or a maj7th chord in the 4th position etc....?
I guess my basic question is, how do I use Triple-stops?
I hope this makes sense!