[Arran]

During the 1937 and 38 model years Philco was big on the concept of what would now be called a "modular" design where they assembled chassis from block sections. So the difference between one model, and another, in the same range, might be the addition of an extra tube in one block section, and the substitute of another tube, serving a different purpose, in another section. That X style cabinet was used with one then one chassis, like a 37-640, I think I've even seen a 37-630 chassis used with it, which is a six tube set by the way, I once saw a Canadian 3118 chassis used in a 3116H cabinet from 1934-35 (had the wrong knobs, so for the price they wanted I passed on it).
Regards
Arran