My Thomas safelight has been "humming" along for about 3 years now. The noise is a bit of a bother, but I'm waiting for the bulb to burn out before replacing it, plus, I have a back up Thomas. Does anyone know what type of ballast and where to pick one up? I suspect the ballast is more the culprit than the bulb, could be wrong, but would like to find a replacement just in case.