The LM3909 tone generator integrated circuit of this application is uncommon nowadays. The circuit can operate on a single battery and is very sensitive.
Found in Popular Electronics from March 1957, this circuit is based on transistors from the time....
The voltage gain of this circuit found in the 1982 SGS Linear Integrated Circuits manual is 10...
This circuit, found in an English publication in 1982, has an inverted sequential effect, as the...