18 May 2024

1950s Switching Power Supply Does it Mechanically

Estimated reading time: 2 minutes

When you hear about a switching power supply, you think of a system that uses an inductor and a switch to redistribute energy from the input to the output. But the original switching power supply was the vibrator supply, which was common in automotive applications back in the middle part of the last century. [Mr. Carlson] has a 1950s-era example of one of these, and he invites us to watch him repair it in the video below.

Most of the vibrator supplies we’ve seen have been built into car radios, but this one is in a box by itself. The theory is simple. A DC voltage enters the vibrator, which is essentially a relay that has a normally-closed contact in series with its coil. When current flows, the relay operates, breaking the contact. With no magnetic field, the springy contact returns to its original position, allowing the whole cycle to repeat.

Opening the device requires a pipe cutter.

You might wonder why you want to make and break a DC circuit in that way. Simple. With a little filtering, you get some sort of AC output, and AC is manageable with transformers, another magnetic device. In a radio, the resulting AC might return to DC to provide plate voltage for tubes. This unit has an AC outlet, although we imagine the voltage coming out would be hard to predict.

In this case, the voltage coming out was easy to guess: nothing. Guessing that the vibrator itself was shot, he tested the coil inside and found it was probably working. However, the unit would not oscillate. Given that it is a 70-year-old mechanical device, this isn’t totally surprising. The next step was to use a pipe cutter to open the can. Cleaning the contacts resulted in the buzzing noise that gave the device its name.

We’ve written before about vibrators and their high-powered twin, the dynamotor (or MG set, if you learned it that way). Many drug store tube testers could also test vibrators.


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