This circuit is from a 60's documentation. The circuit uses components from the era and serves to monitor a 150V continuous power line.
This two-transistor amplifier can be used as power stage for intercom, experimental receivers,...
This circuit was found in a former Popular Electronics. The timing is given by R1 and C1, R4 and...
This two-phase stepper motor circuit was found in an old documentation using an operational amplifier...