As said it sounds like a regulation problem, that is most likely what has caused the bulb to blow as it's overcharging (Assuming this isn't a separate coincidental issue). The regulators can be replaced independently, instead of changing the whole unit.

This is assuming it isn't "Smart charge" controlled, this is a Ford system on newer cars, whereby the regulation is done by the ECU, I think yours will be to old though.

Easy way to tell if to look at the connections, if you have a 3 pin plug, then it's a smart charge setup, but I should think yours will be the conventional setup.

Martin