This circuit is from an old documentation, making use of an operational of the time. The circuit can be adapted to use modern components. The power supply must be symmetrical.
The transducer of this circuit is a small ceramic capsule or crystal earpiece and the frequency given...
This circuit for old flashes with xenon lamps was found in a Radio Electronics magazine from June...
This is one of the many hysteresis comparator circuits the reader may find in this section and on this...