How good are pull-up bars for bulking?

I'm trying to do the bulk (no pun intended harhar) of my working out in my apartment, and I've heard that having a pull-up bar can really help with your back and arms, especially doing weighted pull-ups. Can you build significant muscle, at least in certain areas, with a pull-up bar (and maybe a backpack full of weights) alone?
[not that I'd be using only a pullup bar, but just asking]

Arnold swears by the wide grip pull-up as one of the best back exercise you can do.

FYI, do them with palms facing away to build back the most. Otherwise you're working on biceps.

Yea man, lift yourself till you aren't heavy anymore. Then add some weights and keep doing it. A pullup bar can't be used for every muscle group though, only biceps and back. You can hang from it and do crunches I suppose but you should be working your other parts too.

Yeah I know diet/food is essential, I'm just talking strictly about exercises.

So it's good for widening the back? You mean the lats? That's just what I'd like to improve.....thanks.

Also, that's another thing....is it better to do crunches upside down on a pullup bar compared to, say, on the ground or on an exercise ball?

Oh yeah, and how 'heavy' should I be when doing pullups? Like at what point should I start adding more weight...when I can do 10 pullups? 20? 30?