This 6-tube two-channel amplifier was found in an American documentation from 1947. The circuit is two-channel with a separation of bass and treble.
This 1960s receiver uses a germanium diode as a detector. The phone can be crystal or high...
This circuit is from Popular Electronics. The buzzer is of the Sonalert type with built-in...
This basic version of the timer with the 555 was found in documentation from the 1980s. The relay...