We found this precision circuit in a manual from the 80's. The operational amplifier is of a common type at the time, and equivalents can be tested. Transistors are general purpose types.
The automatic modulated siren circuit shown in the figure really produces an interesting sound...
This circuit is from an Italian magazine Elettronica 2000 of September 1987. It is a pulsator for...
This circuit converts a high voltage into a frequency using an optical coupler. The transistor can be 2N2646...