Antique Radio Resistance Cords

Small radios from the thirties caused plenty of fires back in the day. It was so bad that manufacturers probably should have included a fire extinguisher in the box. The problem was, and is, the resistance cord. In this segment we learn about why old radios have resistance cords and a good method to safely replace them. Antique radio restoration.

You know that song Burning Down the House? Well just listening to it on our old radio could do just that. Burn down your house.

In fact, small radios from the thirties caused plenty of fires back in the day. It was so bad that manufacturers probably should have included a fire extinguisher in the box.

The problem was and is, the cord. Here’s the one from our radio. As you can see it’s pretty thick. That’s because under the cloth insulation are not just wires to power the radio... But a three foot long resistor.

Resistance cord radios are often UN-affectionately called curtain burners. That’s because the cord could get so hot... That nearby curtains could catch fire.

What were they thinking? Well, remember, manufacturers were trying to make these radios as small as possible. As I said earlier, they they did this by getting rid of the transformer. And without a transformer to lower voltage, a resistor was needed instead.

A standard resistor capable of doing the job... Would be too big and run too hot in the cabinet... so they put it in the power cord. Ingenious, really. But also really stupid.

Resistance cords need to be cut out and replaced. But with what?

If I used modern resistor... I’d still have the problems they had 80 years ago.

I do have something they didn’t have 80 years ago, though, and that’s the tiny silicon diode I showed you in the last section.

It allowed me to replace the resistance cord with this circuit I built.

A diode... To drop voltage from 120... To 85 volts. And a resistor... to drop voltage further to 75 volts. Exactly as the resistance cord did... To provide just the right voltage for the tube filaments.

The circuit is small and cool enough to fit inside the chassis. To do that, I drilled a small hole and mounted it with a screw. Here’s the circuit installed and ready to go.

Insert:

As I said during the segment on safety, All American Five radios were fairly dangerous even when brand new. We’ve fixed the resistance cord problem, but we still need to address the hot chassis. To understand what we mean by a hot chassis, it’ll be helpful if we first learn about the hot, neutral and ground circuits in your home’s wiring. We’ll do that in our next video. To stay updated, please subscribe and click the bell. And if you like this video, give it a thumbs up. See you soon.

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