Use heavy negatives on the dip machine for triceps. I absolutely love doing these. It's an effective, safe way to overload your triceps with heavy loads.
Have someone help you do the concentric portion of the lift. Then do the eccentric or negative portion by yourself. Take a few seconds to lower the weight.
Many lifters are making a big mistake when training biceps. They're "missing" parts of the muscle! Are you? If so, these exercises will get you growing again.