My friend has an old and ugly electrical service panel. He does have one free circuit 110/20 with an old screw in fuse. It is however wired properly to the outlet and of a proper gauge. Have a late 80's hotsprings prodigy. Would have come with a gfi pigtail. Any harm to the spa in putting in a gfi outlet here and testing out the tub?
Specifically, Can say the heater be damaged by not being able to draw enough current? I know the house electrical could fry. Whats a house compared to a tub?

Oh, I can help myself out here this older prodigy classic takes a 20 amp not 30 amp dedicated line, so we're good.