Found in a documentation from the 90's, this circuit already includes an amplification stage. The 12 V power supply allows its use in the car.
Found with variations on this site, this circuit was taken from an American documentation from the...
Found in a Radio Electronics magazine from March 1950, this circuit uses a high-power neon lamp...
This circuit was obtained in an 1975 English publication. It is a voltage regulator circuit for...