Photocardiograph (CB21738E)

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

Mechanical Reverberator (CB23995E)
This mechanical reverberator circuit for guitar was found in the February 1970 issue of Radio...
11 to 32 MHz amplifier (CB22024E)
Found in an old English publication this circuit uses a dual gate MOSFET. Coils not specified....
Power Grid Data Receiver (CB4810E)
This is the receiver for the previous circuit transmitter. Similarly, no information about the...