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.
In the figure we have the way to obtain 500 gain from a FET. FETs can be BF245 or MPF102. The...
This circuit was found in Japanese documentation from the 1960s. It is a commercial circuit with...
This circuit outputs a signal modulated by a unijunction oscillator. The circuit is from a Radio...