For a big wide back Wide Chins are great, and when I say wide I mean as wide as you can go. You see a lot of guys just flinging themselves up the bar when doing these and that is something you want to avoid. When you arbitraily pull yourself up you are more than likely using more arms then back. Let you r hands just act as hooks and nothing more, realy contract your lats and let them pull you up. I like starting most of my back trainning with 50 wide grip chins. Usualy takes me 4-5 sets. When I first started doing this it took me 8 or 9 sets. I would do as many as I could until I could only get one rep and then finish off on an assisted machine.
As for dips, I think weighted dips are one of the best exercises for adding mass to tri's. It's one of my favorites, especially super-seted with rope press downs.