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Originally Posted by Chad Hauris
The original model of the clock radio had a mechanical digital clock and a tuning dial which was lighted and curved in an arc...this is why the dial pointer moves at an angle as the electronic clock model uses the same indicator mechanism but a more modern style dial scale.
The electronic version has a unique battery backup system. It uses a 1.5 volt ni-cd cell which is kept charged by the power supply and then if the power goes out, the 1.5 v cell powers a DC-DC inverter circuit to provide the higher DC voltage to keep the clock oscillator going. Often the ni-cd cell has gone bad over the years, though.
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Chad, I have a Zenith H480 AM/FM/FMstereo clock radio with the electronic digital clock and Power Reserve backup system. The NiCad backup battery is still good, even after 26 years. Unfortunately, however, the FM has mysteriously quit (almost--the tuner must be working, as I can hear signals with the volume all the way up) after I tried to clean the slide pots. AM still works as well as when the radio was new. I'm still trying to figure out what I did wrong.
I had a Zenith F472W clock radio with the curved tuning dial and Target Tuning, in addition to the Circle of Sound audio system (the speaker was mounted in the base of the radio). Unfortunately, the radio was lost during a move seven years ago and is probably long gone by now. I should have held on to it, as this was a unique design I have not seen in any other Zenith radio before or certainly since. I have a Sony 3-volt transistor portable, AM-FM, with a tuning indicator in the upper left corner of the tuning dial, but it isn't the same as the Zenith design (although it works on the same principle as the Target Tuning system).