The circuit shown in the figure below is from the 1993 Linear Technology Applications. The operational ones used are uncommon and the use of equivalents can be analyzed.
This circuit can be controlled by an LDR causing an LED to flash at a frequency given by C2. The...
The component used, which is not common today, is an electronic attenuator. In this application of the...
This circuit uses a quadruple operational amplifier of the time. The circuit is from the 70s but...