Try 2x per week weighted holds for example...
Put a 40lb(whatever weight you choose) between feet or legs, get to the top of the pull up (shoulders even with hands) hold for 6-8sec.. then lower yourself to Halfway point (elbows at (90 degrees) hold for 6-8 sec... then lower yourself slightly lower still a small bend in elbow(hold 6-8sec..rest 2 mins and repeat until you cannot hold for 6-8sec any longer or have to start squeeling around when holding yourself up... at that point you are done.. After 2-3 weeks you should feel comfortable starting some type of weighted pull ups. For your goal of bulking there is nothing wrong with 8-10sets of 3 weighted reps.. Also i would start with semi-supinated grip (palms facing one another) gives you the best leverage(easiest) and easy on the shoulder..