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.
This filter for receiving audio in telegraphy was found in a magazine 73 for radio amateurs, in an...
This circuit was found in old documentation. Transistors can be BC548. The LEDs are the same....
The idea of this 1982 project is to attach a photosensor to a telescope to convert into sound...