This was a very early ‘powered’ remote speaker. Early speakers did not have the advantage of the powerful rare earth magnets we have today. These speaker used electro magnets, so a remote speaker like this dynamic 80 had to provide magnet power. They did so with a small transformer and a selenium plate rectifier assembly. We updated this speaker to use a modern silicon diode, while leaving the selenium rectifier assembly in place, but disconnected. When selenium rectifiers go bad, they smoke and smell really bad. We then added a miniature plug cable so you can play your mp3 player through it. Real vintage.