This precision signal rectifier was obtained in an American technical documentation from 1975. The operational amplifiers can be 741 and the power must be supplied from a symmetrical source.
This simple signal tracer was found in a Popular Electronics from the 90's. The transistor can be a...
This configuration for latching automation using relays was found in Radio Electronics magazine from...
This circuit is from an old Italian publication, being used in record players with crystal...