This circuit is from Delco Radio found in a 1968’s documentation. The transistors are of the time and are not given information about the driver transformer. Note the high supply voltage.
Found in a 90s Popular Electronics, this touch switch uses a single sensor. PLLs are common today....
We found this circuit in an old documentation from 1979. It is a logic level tester that is...
This ultrasonic insect repellent was found in American documentation from the 1980s. The...