Thank You, Brother!
If I had to pick one exercise for building biceps, without a doubt I would select preacher curls. Actually, now that I think of it I wouldn't either. I would pick "Scott Curls." It's really the same exercise but there's a big difference in the equipment. A preacher bench can be anything with an arm rest on a stand. But a Scott bench has a very specific design.
Over the years, I have worked on the design of this little bench to where it is as close to perfection as anything I've ever seen. When it's designed correctly it's great. If not, it's lousy. The normal flat faced bench is not very good for anything let alone bicep work. Even plain old standing barbell curls are better. But let's assume you have a well designed bench with at least a convex face.
The key to this exercises working its magic requires several specific techniques. The exercise should always be done standing rather than seated so you can get your hips under you when the weight gets heavy. The seat's only on there to give the bench more strength and for other seated exercises like seated DB presses, seated curls, etc. But whenever you're doing Scott curls you should always do them standing.
The most effective system I have ever used is aa tri-series as follows:
First get a pair of dumbbells with which you can just make 6 reps. Then get a barbell that's about 70% of the weight of the dumbbells. Finally get an EZ curl bar and load it with 80% of the weight of the dumbbells.
For example, I use 70 pound dumbbells (140), a 100 pound barbell and 120 pounds on the EX curl bar. Now you're ready to do some serious work.
It's best if you have a training partner for this exercise because it establishes your pace much better. You do your tri-series then he does his. The rest time is just about right.
Start off with the DB Curls. Place a towel on the bench to keep your skin from catching on the naugahyde cover. This exercise is done in a fairly loose style. You don't have to get the armpits right down on the bench. For this to work, the face of the bench needs to be not only curved but short enough to keep the dumbbells from hitting the bottom of the bench. It doesn't matter if you cheat to get the dumbbells up. You do however, need to let the dumbbells all the way down and COMPLETELY UNCURL the wrists at the bottom of the exercise. This is important because it's the bottom of the exercise where all the growth lies hidden. It's okay to pull back with the shoulders to assist in getting the weight back up to the top. The 6th rep, however, should be really tough. In fact it should be just about the last rep possible even on the first tri-series. Once at the top of the 6th rep you then need to do at least four 1/2-rep burns. They're done by letting the weight down so it's about to fall then bringing it back up again, burns in the upper, top range of the movement.
If your bench has a flat face, this movement is murder on the arms and elbows. You need a well padded, rounded face for this exercise to work.
Next, set the DBs down and immediately, with no rest, pick up the barbell with a wide grip. Approximately 4 inches wider than your shoulders. You should have the palms heavily chalked to keep them from slipping. Wrap the thumbs around the bar (don't use a "false" grip). Nestle the armpits clear down on the bench (the bench needs to be well padded on the crown to eliminate any armpit pain). Let your feet forward so you are really resting on the bench with the body. slowly lower the barbell with the wrists curled until you come to the complete bottom of the exercise. Uncurl the wrists totally. Then with no movement of the upper body whatsoever, slowly curl the wrists and force your arms to come up. Do not cheat even a smidgeon. This takes strong forearms. Because you'll find you'll fail in getting your wrists curled. Quite often your biceps are strong enough but it's your forearms that can't hack it. If you want beautiful lower biceps, you have to build strong forearms along with the biceps.
Keep the shoulders and the head forward. Look for ways to make this straight bar exercise of the tri-series even more strict. it's the key to the whole thing working. The dumbbell and the EZ bar are important but nothing like the straight bar with strict form. All the growth is hidden in this middle exercise. It's also where the pain lurks. If you're patient with yourself and endure the pain, the bar will come up very slowly, but it will come up. You must have faith and be willing to endure the pain of this exercise. It is excruciating. But it is the heart of the series. Don't cheat at all. Do 6 reps with 4 burns on the top as you did with the dumbbells.
Set the barbell down and immediately pick up the EZ curl bar with a reverse grip. You'll really need the chalk here. The weight should be so heavy you can just barely make 6 reps. Your armpits are not down on the bench for this movement. The form is very similar to the one you used for doing the DB curls. You are trying to use a heavy weight on this exercise just as you were on the dumbbell curls. It is the DB curls that are done strict. do 6 reps and 4 top burns with the EZ curl bar also. You will have just done one series. You can then rest long enough for your partner to do his series. You should do anywhere from 3 to 5 series.
It is a killer but . . . you won't believe how much progress you'll make on your biceps. I know of nothing like it to build incredible Biceps.
Enjoy Your Lifting!