The circuit is from 80s Siliconix documentation. The integrated circuit is from the company and is not common today. It can be used operational equivalent more common in our times.
This circuit is a from publication 1980, but still can be mounted with BC548 transistors for Q1...
The output voltage is adjusted by the trimpot. The power transistor mist be mounted on a heatsink. The 3.9...
This basic configuration of an astable multivibrator was found in a publication of the year 1968....