This circuit was found in the December 1992 Radio Electronis magazine. R2 is an NTC, there is a MOV protector or NTC thermistor. The current depends on the thermistor used.
This 300 Hz to 3.4 kHz filter was found in the May 1989 Radio Electronics magazine. The circuit...
This circuit used in signaling for boats, cars or barriers was found in a 1980s documentation. It still...
This circuit was found in a NASA documentation from the 1980s. Component values are application...