We found this circuit in a 1971 documentation. The circuit can be assembled with more modern transistors such as BC548 for Q1, BC558 for Q2 and BD135 for Q3.
We found this commercial circuit sold as PT-40 in Japan in the 1960s in a documentation of the...
This audio oscillator can also be frequency controlled by an LDR. The circuit is from a 1975...
The circuit shown in the figure is triggered by an input voltage determined by the setting of P1....