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The B&W Thorn uses a transformer to isolate the mains from the chassis and supply 6.3v for the heaters. The same chassis was later designed as a series heater string again using the transformer for isolation and filament supply. This was done to help reduce the heat produced in the transformer.
Not many B&W sets in Australia had hot chassis. Those that did used a few different methods to drop the supply voltage for the heaters. One popular method was to use a diode in series with the heaters to give 110v half wave AC.
I'm surprised to see "our" 3 pin socket used in the US. Since the voltage is similar I guess they considered it safe to use there especially since Australian spec electrical equipment would be most unusual in the US.
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