This circuit with unijunction transistors was found in a documentation from the 80's. The trigger times of the SCRs depend on the capacitors and are adjusted in the 5M (4M7) potentiometers.
We found this circuit with PUT in an American publication from the 1980s. PUT is not a common...
The frequency of this oscillator depends on the crystal used and the transistors. The circuit was...
This circuit is from 1977 documentation, but can be assembled with BC548 for Q1, Q2 and Q4, BC558...