Photocardiograph (CB21738E)

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

fet infrared Modulator (CB14681E)
The circuit shown is from the Texas Instruments optoelectronics manual, applying to low power...
High Impedance 2 W Amplifier (CB6163E)
This circuit was found in a 1968 General Electric documentation. It has an input impedance of 2 M ohms...
Twin-T Rejector Filter 741 (CB25603E)
This filter that rejects a frequency range determined by the double-T was found in the August 1993...