[Arran]

I don't totally agree with that, for one thing the tube technology did improve after 1938, eliminating the grid caps and the introduction of shorter envelopes lead to smaller interelectrode capacities. Also many of the early 1940s sets incorporated an FM band, which was supposed to be the next wave in radio broadcasting (though it took until the late 1950s for it to catch on everywhere) Some of the best communications sets constructed were built during the 1940s and 50s. I would say that some of the better designed Philcos in this era were in the Tropic series of models, some of which were also manufactured as Canadian market models.
I believe too many people focus on tube counts, in which case the 1936-38 models win out, but many manufacturers were notorious for "Tube Stuffing" a chassis in ways that really did nothing for the performance. I've noticed that one of the favorite tricks in this period was to use a single triode for a first audio amp, and then to use a double diode like a 6H6 as a second detector, when they could have used a 6Q7 or a 6R7 in it's place. Then you have the magic eye tubes, which are a nice gimmick but do not do anything a light bulb or a shadow meter could not do.
I have also noticed that many of the sets sold from 1936-38 (other then Philco and RCA) have shortwave bands, but they have a rather useless band spread. They typically have a "Police Band" which runs from the upper end of the standard broadcast band (or just past it) to maybe 3.5-4mc, maybe it was active once but it's a dead zone now. Then they follow that with a shortwave band that attempts to cram everything from 5 mc to 22 mc on one scale, with the upper frequencies crowded in at one end.
Regards
Arran