This circuit for very long-time intervals was found in the March 1993 Radio Electronics magazine. Times of several days or even weeks can be achieved depending on the value of C1.
This old oscillator using germanium transistors has a high impedance headphone as inductor to...
This old fashioned amplifier can source some watts to a low impedance loudspeaker. The circuit...
This 50 Hz rejector or notch filter was found in a 1975 documentation. Other frequencies can be...