[Arran]

Joe;
These chassis are not that large by length, or width, but they are quite deep, I have a feeling that these were a carry over from the RCA R7 "Nipperette" style chassis, which were a carry over from the 1931 model year. The main difference being is that the tuning condensers on those are under the chassis, as is the B.C band oscillator coil, antenna coil is on top. These have five bands, and the bandswitch/coil assembly is under the chassis, to renovate one of these radios properly you have to remove that coil assembly/catacomb to access the bottom of a number of the tube sockets. I really don't think that servicing was what RCA had in mind, just convenience of assembly by building the set with basically "modules", so I'm guessing that not much went wrong with these over their anticipated service life other then maybe filter cap changes.
Then again it could have been an offshoot of the 1930s trend towards miniaturization, packing the maximum amount of radio in the minimum number of square feet. My Echophone S5 certainly fits that bill, eight full sized tubes stuffed into a chassis the size of a average 1940s AC/DC set.
I remember reading in an old industry magazine that surveys indicated that these sets were typically kept for between 10 - 15 years before being traded in on a newer models. In reality the Austrian painted and the Empire of Japan had a hand in extending the service life of many of our sets, between production being halted in the spring of 1942, and tube shortages, it does explain why so many early AC sets are still around. It was easier to get tubes for your RCA Radiola 18, and your Philco 95, then it was for an early 40s AC/DC set.