Found in a 1960s RCA manual, this circuit uses components from the era. For the indicated circuit R1 is 28ohm and R2 is 1 k.
This integrated circuit is recommended as a standard amplifier in sound equipment, TV sets,...
This circuit was taken from a popular 90's Electronics. The LDR is mounted next to the LED to feed...
This circuit with the operational amplifier CA3130 was found in an English publication from 1977....