Zenith – Model ZE-16 Filter Unit 392 392A Schematic – Gernsback
In the early days of radio, If you used commercial power, not only did you need a separate power supply, but you also needed a filter unit to surpress line noise – these became standard a few years later – a natural evolution of the radio
Apparently battery power was very common in the early days of radio, using batteries that lasted for several hundred hours, but were disposable
Using power supplies were a natural evolution to limit buying batteries
Zenith – Model ZE-16 Filter Unit 392 392A Schematic – Gernsback
