[Arran]

It looks like they followed the lead of Canadian Marconi, they used two smaller gangs in the tuning condenser for short wave reception, so it's a four gang tuner, kind of like some AM/FM sets have. What stinks is that that the cheapskates only have one IF amplifier, but used a separate triode (6J5) connected as a detector diode, then used another triode as a 1st audio. They could have added an extra IF amp in that socket, and used a 6Q7 as 1st audio, detector/AVC, or a 6B8 as an IF amp and detector. Phonola/Electrohome used to add an extra IF amp without adding a third IF can all the time in their battery sets, so I'm not sure what the guys at Philco were thinking. My guess is that the model 54 is based around one of the U.S made Tropic models, at least in the front end, though I don't recall Ron running into one with separate sections in the tuning condenser for the shortwave bands. 
Regards
Arran