Maybe it’s a hand-me-down from an elderly relative. Maybe you found it at a flea market, or it has been hidden in the attic for far too long. It could be an anonymous-looking black box with big dials ...

With each passing year, more old radios succumb to “passive” death. The tubes may still be working, but paper capacitors dry out and crack open. Electrolytics gum up and short. Carbon resistors and ...