So, what is this jar? It’s a power diode. What?
I’ll explain in a minute. First, some background. Early radios ran on batteries. Power supplies that allowed radios to be powered from an electrical outlet added too much cost at first to be added to an already expensive radio. By the late 1920s AC-powered radios were popular. An intermediate solution was after-market power supplies that allowed you to power your battery radio by just plugging it in.
In the mid-1920s there were not a lot of economical ways of converting AC to DC. You could use rectifier tubes or some primitive solid state diodes.
Here is an RCA Duo Rectron power supply that used a rectifier tube and a ballast to stabilize the supply voltage. It was a pretty expensive unit at $65 in 1925.
This Majestic power supply used a cold cathode rectifier tube (Raytheon’s first product) to supply the high voltage and an early high power solid state diode for the low voltage.
But Philco choose to use the bottles like the one pictured above. When filled with the right chemicals, an oxide would form on one of the electrodes that only allowed flow of electricity in one direction.
Four of those little jugs were arranged as a diode bridge in Philco’s radio power supply to turn house current into DC. They were not very efficient so the unit made a nice room heater as well.
I have read about one collector who mixed the right chemicals to get one of these working again. Radio magazines in the 1920s listed the right mix in articles for those who wanted to build their own supply.
Philco’s power supply had a transformer, the chemical jars, as well as inductors and capacitors for filtering.
There was one other component—a light bulb. Turns out that every time you turned on the power supply, a new coat of rectifying oxide had to be formed. For the few seconds during which this process took place, the rectifier bridge was a dead short. The light bulb acted as a ballast to absorb the power until the power supply began to operate properly. So goes the strangeness of transitional technologies!