Hard to say. I think for most servers, there is very little conscious muscle contraction in the bicep, but the arm needs to stay bent. I believe video shows that you need to maintain a right angle or less to serve efficiently. So rereading your query, you don't want to try to drop the racket using the bicep, you want to use the torso and shoulders to drive the elbow up and let the hand and racket lag into the drop.
I often see people have trouble with serving because they keep the arm too straight in the trophy position. Make sure you have the bend in trophy and try to relax the arm as much as possible. As the hand moves up to the ball, the triceps will do most of the action, so actively tensing the bicep will probably slow the arm.
Last edited by WildVolley; 01-27-2013 at 10:49 AM.