Solid state relay (CB8518E)

This circuit was found in a 90s Popular Electronics. Both the coupler and the MOSFET can be of any type.

Transistor Test (CB23589E)
This small general purpose and RF transistor tester appeared in a February 1958 Radio Electronics...
Biquad Filter MC4741 (CB14466E)
The MC4741 integrated circuit consists of four operational amplifiers similar to the 741 in a...
Touch Switch (CB6451E)
We found this touch control on a Popular Electronics from 1970. The circuit makes use of an...