[Jeffhs]

I remember seeing a picture of an RCA Radiola III in the (now long defunct) Popular Electronics magazine years ago, in an article titled "Restoreth Thy Relic Radio". However, that oval-shaped hole at the upper right corner of the cabinet originally had a piece of clear plastic over it. (This cover appeared broken in the Radiola III photo I saw in the article.) It was centered on the single WD-11 tube, and could have been there to show the tube filament so the user could tell if the set was on or off; this is just a guess, as I don't think the filament of a WD-11 operated on batteries would glow anywhere near bright enough to be used as an on-off indicator. Maybe it would glow bright enough to see if the set were operated on a battery eliminator, if such was even available when these radios were new -- which I doubt. The Radiola, and its predecessors, were likely one of the first commercial radios designed for home use and to be powered only by batteries. I don't know whether AC power was available in homes in the 1920s, but if not, I would think the Radiola III would have been designed for battery-only use. I'm sure these sets would have been instant best-sellers in rural areas without electricity (prior to the enactment of the Rural Electrification Act in, I believe, the 1930s) as well.