Thoria is a slang word used in the tube manufacturing industry such as at the Towanda plant in PA that built filaments. It is actually called thorium. The post clearly states early failures (loss of emissions) of the Chinese 811A & 572B tubes. The tubes have to have thorium used in the filaments or they would not function correctly due to the low filament operating temperature as seen by the color (yellow-white). In other words non-thorium filaments at the low operating temperature would produce a weak (low emissions) new tube at best.