This receiver was found in a Popular Electronics from the 90's. Its different configuration shows a tuning circuit after the tube that works as an aperiodic amplifier. Observe supply voltages.
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...