This circuit is from Radio Electronics from March 1977. The integrated circuit is from that time and the circuit is intended for an infrared audio link. The modulation is in pulse frequency.
This VCO or Voltage Controlled Oscillator was found in a Popular Electronics from 1991 but can be...
This simple circuit was found in Popular Electronics from 1992. The transistor is a...
This type of circuit is widely used in old cassette recorders and tape players, regulating the...