The ballast is the real heart of the system. I always buy new ballasts but heads can be used. Have spare ignitors and everything else is pretty easy to deal with. Having spare ballasts is always a good idea. I use power-to-light ballasts and so far not one problem in several years. You can basically make any ballast work with any head. I have LTM, Mole, Arri heads and all work off the same ballasts. You can either make adapters or unify the connectors and pin configurations. Im using Mole/Cinemills and have converted all to that. I also make all my own head feeders. This is crucial. It doesnt wind up cheaper, but this is one area you dont want failure because its so easy to keep from happening. If a ballast goes because of an internal failure then at some point that cant be helped. If it goes because you had a head feeder failure, that is avoidable, that it a terrible feeling. More often then not people dont even want to open a connector and look inside. This practice is scary. If you havent inspected your feeders then do so before using again. Do get a spare. I suggest a new PTL ballast and use the one you have as the spare.