Ultrasonic Proximity Sensor (CB21312E)

This circuit was found in a Popular Electronics from the 90s. The circuit uses a ceramic capsule as an emitter and detector.

Battery Charger (CB4388E)
This circuit, obtained from a 1965 magazine, can still be assembled using some modern equivalent...
Full wave power supply (CB22340E)
This source was obtained from a book on transistors from the 60's. The circuit uses germanium...
40W Voltage Inverter (CB25375E)
This powerful inverter provides a high-quality sine wave signal. I found it in a Radio Electronics issue...