This circuit appears on this site from different sources. This is from documentation from the 1980s. The operating system used is uncommon and can be replaced by a more modern equivalent.
This repellent operates with frequencies from 30 to 45 kHz, serving for insects and rodents. The...
We found this preamplifier with 70 dB gain for microphones in American documentation from the...
This circuit can be used in measurement bridges. We found it in the September 1995 Electronics Now magazine....