Lately I have been getting bubbles - more like a pimple - in my cheesecakes . Basic recipe hasn't changed , any suggestions ?

I suspect you are overmixing the batter, thereby creating air bubbles which rise to the surface while it is baking. If you are adding your fruit as a puree, all you need to do is remove about a cup of cheesecake batter, stir the puree into it, then swirl the mixture back into the rest of the batter. You won't need anything additional to set the bake other than the eggs, which will do a fine job. Just be sure to always mix on low speed.