9V power source (CB21164E)

This simple circuit with a 5V regulator was found in an American documentation from the 90's. The output voltage is adjusted in a trimpot.

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Switch Amplifier (CB21820E)
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We found this circuit in a 1992 Popular Electronics. The circuit has an optical sensor with LED...
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I found this circuit in an old English magazine from 1979, but it can be easily assembled with...