I think the device is more commonly called a dynamotor. That's dynamo plus motor, and dynamo is generally accepted as the term for a DC generator. It is true that this setup would have trouble responding to a changing load, but a good design for a radio has high immunity to swings in B+ voltage. Tube or transistor, in my hobby work I avoid designs that have any great dependence on either the exact supply voltage or the exact characteristics of the components. Someone mentioned the "ground return." I don't know that anyone, for any large scale power generation, ever used the ground as a return for the power, one wire as one leg, the ground as the other. The "ground return" is used for unbalanced consumption because the current is generated as three-phase and generally consumed as single phase. The three legs of the supplied power from the generating station will never, ever carry anywhere near the same wattage. This is why the center tap on the secondary side of a "pole pig" is grounded and it is also the neutral line. The house ground is for grounding electrical boxes, switches, and outlets. The neutral is not a good substitute for this. The house ground's function is to prevent electrical shock. If a wire comes loose in your appliance the electricity goes to ground, not your fingers. One problem that I think that people will find in a DC line is that each line acts as a heavy-duty condenser. If you have a wire in the first place that is insulated from the ground its mass will charge up to hundreds or thousands of volts and when you have runs kilometers long that's a lot of stored energy. It's a really good idea to have drains here and there.