Cant forget that tris are almost 2/3 of the upper arm man! Kill the tris and size will come, quick. But you need to maintain symetry too...
A good routine i used for a month only training arms twice a week was this, worked well. Got an inch!
(3 sets 12 reps per set, pyramiding)
Bi's: BB curl, DB pronated curls, EZ bar 21's, High cable D ring curls, EZ bar heavy preacher curls, Concentration curls, DB cross chest curls.
(yes thats ALOT, but if you're supersetting which i'd suggest you will break those muscles down waiting on protein)
Later that day...
Tri's: V bar cable pushdowns, Rev. grip flat bar push downs, High pulley D ring cable kickbacks (underhand grip), seated single DB two handed overhead press, Incline skullcrushers, French press, and weighted dips.
I can GAURANTEE if your protein habits are on point as well as sleep you will make good gains off of this setup, and mind you this is only 8 times a month at twice a week....