This circuit is from General Electric from the 80s, using a relay with high current contacts (20 A). The transistor admits equivalent, and any phototransistor can be used as a sensor.
This amplifier is from a May/April 1969 Popular Electronics. The components are from the period and...
This circuit may be used in IF steps of dual-conversion receivers, i.e., a type of receiver that uses...
This 555 IC circuit was found in the November 1994 issue of Radio Electronics magazine. The...