[Arran]

I would not try electrolysis on what you might think is pot metal, zinc, aluminum, etc, it apparently will not take well to it so I would not experiment on something you care about. I usually use washing soda, some use baking soda, which are fairly benign, but it is not the chemical that does the damage but the current flow from the electrolysis itself since it is an alloy. By 1939 the formula for pot metal was largely sorted out, it was very commonly used in trim parts on cars during the 1940s and 50s, pitting is common, but not deforming, and disintegration like in late 1920s radio parts. Apparently what causes the problems in 1920s radio parts was contamination with lead, which may explain why some parts fall to pieces whilst others fair much better on different examples of the same makes and models of radio. I would stick to chemical strippers (not lye based), you might also try boiling or steaming the cast parts. I'm not sure about brass, I don't think it will be harmed though, but the process is usually for steel or other ferrous metals. The condition of this radio lamp is what made it an easy pass for the price, in my opinion, but the deal is done now.
Regards
Arran