This circuit was found in a Popular Electronics from the 90s. The transistors are general purpose, and the gain depends on the ratio between R2 and R1.
This small general purpose and RF transistor tester appeared in a February 1958 Radio Electronics...
The MC4741 integrated circuit consists of four operational amplifiers similar to the 741 in a...
We found this touch control on a Popular Electronics from 1970. The circuit makes use of an...