Photocardiograph (CB21738E)

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

Component Tester (CB4313E)
This circuit consists of a simple continuity test with two transistors forming a relaxation...
100 W Inverter (2) (CB13974E)
This circuit is a manual of 1972 RCA power transistors. The critical components of the project are...
High speed trigger (CB21850E)
Found in the 1974 Ferranti transistor manual, this Schmitt trigger circuit uses general-purpose transistors...