Photocardiograph (CB21738E)

We found this circuit in a 1969 Popular Electronics. It measures the heartbeat by changing the transparency of the finger.

15W MOSFET Amplifier (CB1000E)
With a 22 V symmetrical power supply this amplifier provides 15 W of output power with excellent...
5 Voltage Level Indicator (CB4892E)
This circuit is based on an uncommon Texas component today, as found in an American 1980s...
741 VCO (CB24052E)
This voltage-controlled oscillator or VCO was found in a Radio Electronics magazine from July...