What you want to do is to NOT use that device with the selenium rectifier, because when those go bad, they emit highly toxic fumes. Now in the refining world, we deal with fumes that are among the most toxic there are, eg; NO2, and HSe is less toxic but still pretty nasty.
What you want to do is to buy either an encapsulated bridge rectifier consisting of four diodes, or, 4 individual diodes. I heartily recommend the encapsulated type. You bolt it to a piece of metal for a heatsink. You want about a 25 amp and better, a 35 amp one. About $5-7 buying them one at a time. They look like this:
Enquire further if you need any electrical coaching. There are two connections labeled "~" which is where the AC from the transformer connects. There are two connections labeled "+" and "-" and you are replacing the old selenium deal with this new thing, wire for wire. It's small, about 1-1/2" square, and there's no particular need to remove the old rectifier from the cabinet. Just leave it there, unless it's easy to remove. One machine screw through a hole and it's mounted, done. Nice if you have silicone goop that can conduct the heat,
and helps keep corrosion out, if you don't, that's probably OK. See if you can buy a little tube of silcone thermal grease for $1 wherever you buy the bridge. Just get a clean interface (sand and steel wool it) between the bottom of the bridge and whatever piece of metal you mount it to, the cabinet or the internal chassis, and have that piece of metal be or large area.
