Found in a 90’s American documentation, this circuit indicates the frequency of input pulses up to 1 kHz. The circuit has a very explored configuration on this site.
This oscillator with crystal for overtone operation was found in an old American documentation. The coil...
This test consists of a simple Hartley oscillator using a transformer of the type found on older...
We found this circuit in an American 1980s documentation. The transistors can be equivalent as BC548...