Found in old documentation, this source uses an integrated circuit from that time, which is uncommon nowadays. The power source has a ripple below 1 mV.
This circuit receives the local stations of medium waves listened to in a piezoelectric capsule or...
This circuit was published in an 80's American documentation, but it is still current. The power...
This simple neon lamp power indicator circuit was found in the January 1971 Radio Electronics...