This circuit was found in a 90s Popular Electronics. It generates tones given by the oscillators and can be changed. The circuit already includes an amplification stage.
This timer, like the previous circuits, uses a currently uncommon integrated circuit. The time is...
Found in an EEE this circuit uses FETs of the time and a bipolar one. Current equivalent...
This ultra-simple receiver has in the tuning circuit a variable capacitor for AM and a coil,...