How do car radios work?

How did the mechanism of preset stations in old car radios work?

• Old car radios had push buttons that physically dragged the station tuner back to a memorized location. What was the internal mechanism that made that work? (To clarify, I'm not asking about the relationship between the position of the station and the radio receiving at the correct frequency. I'm curious about the physical mechanism that enabled station locations to be memorized and then recalled by pushing on those buttons.)

• Answer:

  These used a remarkable mechanical system that will make your brain hurt (like trying to figure out an electric typewriter) but there were few electronic options at the time. Virtually all tuners used either tuned inductors (coils) with iron slugs sliding in and out, or rotary variable capacitors to change the frequency (aka "that knob on the right") and a spring-tightened string that would slide along a track according to the rotation of the capacitor's shaft for the dial position indicator. There was a set of mechanical linkages that would rotate the shaft to the preset station; you would pull the knob out, turn to the station, and then push the knob back in to "set" the spot it would later return to for that station. Here's a photo that shows one of the common Delco internal mechanisms, and a link to a good page on understanding and repairing these little marvels (which is also the photo's source). http://www.jalopyjournal.com/forum/threads/tech-fix-a-stuck-radio-pushbutton.300238/ BTW, these older car radios usually had amazing AM tuners, because people were expecting to get good AM reception far from cities back when stations were fewer and often weaker and FM was not as common (many didn't even have FM). Some radio fans even take these units and use them for long-distance AM listening as a hobby in their homes using a 12v DC power supply and a long-wire antenna. Anyone remember the really old ones with a dial marking that was a circle with a triangle inside it for the two AM Civil Defense emergency frequencies?