This circuit detects when there was a power cut, triggering the indicator circuit around it. The circuit is powered by the voltage of a source connected to the grid.
This circuit for crystals from 100 to 500 kHz was found in an American documentation from 1954. The...
This amplifier with two FETs in direct coupling (cascode) was found in a 90s Popular Electronics. The...
Suggested by an American technical documentation, this circuit is polarized in order to provide an...