[Arran]

I've had good luck using a wad of paper towel, soaked in vinegar, on thick crusty rust that the usual rust removers won't touch, I fixed up the chassis in a Stewart Warner 6 volt battery set that way, cleaned it off, then applied phosphoric acid to the bare but pitted steel. I came up with that after trying muriatic acid on an even rustier chassis, it was nasty to work with and didn't really work all that great, I think I finally took a wire wheel on an angle grinder to get rid of the last of it, after I drilled out the sockets rivets (pushing them bellow the chassis), and removed the other chassis top parts that were in the way
 I don't know whether they really did use cadmium plating on Philco, or any other chassis, the older Philco chassis ook like they may have been zinc plated as they are a dull dark grey colour. Are there any home test kits for cadmium like there is for lead paint? I suspect that many chassis may have bee plated with tin, as that is what they used on tube shields, why use two different types of plating on the same chassis. Some companies, liek Stromberg Carlson used copper plate, and then switched to zinc chromate, which is a yellow colour. 
Happy Christmas
Happy New Year
Arran