Audible Voltmeter (CB21395E)

This circuit was found in an American publication from 1969. Transistors are from the time and can be replaced by modern equivalents.

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Fuel Low Warning (CB24111E)
This circuit was found in the April 1971 Radio Electronics magazine. It uses common transistors and can...
Telephone Scrambler (CB23524E)
This voice scrambler and descrambler circuit was found in a Radio Electronics from July 1963....
Ladder Generator (CB21245E)
Using a 4017 as a base, this circuit from a 1990s Popular Electronics generates low-frequency...