I have recently scored a couple of NOS (more recent than old) Cooper RMA in 100W HPS. I bought them with the intent of changing the ballast to something unusual for a NEMA head. Everything was going according to plan until I discovered that the HPS ballasts are welded on the mounting plate instead of screwed on. Now I need to figure out what to do. Is it easy to pop off the ballast (ie break the weld) and reuse the bracket, or is it easier to find some other metal bracket to use instead ?

I just cut through the welds with a handsaw or dremel, file down what's left, drill holes through for machine screws with bolts, and then screw down a bracket similar to what's in the pic below. I don't know the official name for them but you could probably make something yourself without too much difficulty.



Out of curiosity, what kind of ballasts are you planning on putting in?

Yeah you can always just cut off the welded bracket with a Dremel, grind the remaining welds off, drill and tap for new ballast.

If you want to keep the original assembly intact you can, get the same size metal bar from Home Depot/Lowe's/Princess Auto/Metal Supermarkets, drill and tap the correct holes, using a vise or a vise mounted bending brake, bend the metal to the correct shape.

I'm currently midway in a similar project to build a CMH retrofit kit for one of my Powerlite gumballs that can be fully reverted. Unfortunately the ballast I bought doesn't fit so the new bracket I made is only being used to hold the new G8.5 lampholder.

Thanks for your replies. It sounds like making a new mounting bracket will likely be the easiest way about this.

I'm thinking of using a 50W MH ballast less ignitor for 75W mercury lamps.