I recently painted a Westinghouse OV-25 in metallic gold and am looking for a light source for it. I don't own any low-pressure sodium fixtures so this could be a good opportunity to change that. I already have a 35w LPS bulb that should fit within the fixture if I can get a base adapter. The biggest concern is the ballast, I did some looking online and wasn't able to find one. I had seen the member Parrot had used a Workhorse 3 ballast to drive a sodium lamp but I don't know enough to know if that is what I should use. If someone can point me in the direction of an affordable ballast I would be very appreciative.

 Not sure if they make an adapter.  You may have to swap out the socket for a BY22D socket . https://www.ebay.com/itm/144423140859  Someone here might have one for cheaper . I don't know anything about the workhorse ballasts. I do know that the 35w & 55w are the same ballast .

There are at last E27 to B22 which should be acceptable for my purposes. although a socket replacement would be stronger I don't know how the reflector would fit in because it relies on the E-39 socket for support.

I ended up using a Workhorse 5 with three leads (cap the 4th lead) to run a 55w lamp in my Beta 6. The original ballast was dead. The WH-5 was actually a better fit as it was more similar in shape to the original ballast (F-Can) than a core and coil ballast kit.

Those E27 to B22 adapters do work in cobraheads and I got them to fit into a E39 to E26 adapter for use in a cobrahead. Figureing out the lamp support on the far end might be a problem but I suppose if the reflector is screwed in you might be able to use it to mount a wire support.

Yesh, the reflector is a sproing mount but I think if I mount the support directly to the reflector it should be fine.

I have some experience with SOX ballasts. Workhorse ballasts for years have been proven to run SOX lamps satisfactory. Obviously not as good as a legit ballast (let’s say a Advance), but to where the lamp operates close enough to its intended ratings.

For what your looking for, a Workhorse 3 (WH3-120-C) would be your best option, especially if you want something affordable since a WH3 is the lowest tier you can go with 35W lamps. It may slightly under-drive the lamp, but it will run it and seen a few members do it.

WH3s run in the $30 range with most suppliers and on Amazon.