Found in American documentation from the 90s, this circuit uses a high voltage relay and has no grid isolation. The high values of R1 and R2 prevent the shock when it touches the sensors.
This circuit tests quartz crystals of frequencies between 100 kHz and 10 MHz. The circuit is from...
We found this circuit at a January 1991 Modern Electronics. The magazine no longer exists, but the...
The ZN416E integrated circuit is uncommon today. It consists of a complete radio, like the one...