This circuit protects the speaker from dangerous direct currents that could damage it. The circuit is from an Electronics Experimenter Handbook 1993 edition.
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...