[PeterN]

I was wondering if anyone knows if these AC/DC transformer-less sets were actually used on 110v DC anywhere, and when.

I read that the model 40 (1929) was actually made for 110v DC only. I expect that consumers in the "eastern seaboard" states, that were using the Edison System (New York) during the early days of electrification (1890's), would be likely 110v DC users, but that would have been long before radio really caught on, when most power distribution systems had been "standardized" on 110/220 AC. The "All American Five" transformer-less sets didn't really make a prolific appearance until after WWII when everyone was using 110v AC.

I find it interesting that the "transformer-less" sets mention AC or DC operation in their operator/service manuals and go so far as to mention that when running on 110v DC, if no sound is heard, reverse the plug.

I have searched the Internet without success, looking for any history that tells when and where 110V DC was used in the home, after the radio era began. 

Thanks in advance.