This circuit was obtained from an American 1980s documentation. The frequency depends on the crystal and the circuit may be a PNP that reaches the generated frequency.
This circuit was found in a 90s American documentation from the 90s. The components are from that...
This circuit is intended to monitor the flame of gas heating systems that must always have a small...
This configuration has already been found in other manuals, as the LM117 is manufactured by...