This proximity sensor was found in a 90s Popular Electronics. The base is a PLL567 that operates at around 100 kHz. The circuit operates by capacitance sensing.
Found in an older Radio Electronics, this circuit generates signals that can be used with regular...
This circuit was obtained in a manual of operational amplifiers of 1973. The circuit uses...
This is a battery powered 3W power amplifier using germanium transistors. The circuit is from an...