[Arran]

Those bias cells are an odd idea, but they are (unfortunately) quite common in Canadian Rogers, and Canadian Marconi sets, most of those use two of the wretched things. I could be wrong but I think the 37-604C may have been the only Philco model to actually use a Mallory bias cell, I don't think that even their battery operated radios did, they had "C" batteries sometimes, but not under the chassis. I have a Canadian Stewart Warner 6 volt set that uses a pair of them, in series, under the chassis, which is a little more understandable since the set uses battery tubes, so directly heated cathodes/filaments but I could never wrap my head around why an AC operated radio should incorporate bias cells when there were plenty of competing makes and models that never used them. In the case of Rogers built sets, my 10-60, a 1935-36 model does not have bias cells, they used cathode resistors, and bypass caps instead, those silly bias cells really seem like the answer to a question that nobody was bothering to ask. Even the question of patent royalty avoidance doesn't make sense since all companies in Canada belonged to a patent pool, which is why you occasionally see a Philco model with a factory installed RCA jack.
Regards
Arran