This simple circuit was found in a Japanese magazine in 1967. The circuit is listening on a headset and the coil is 50 + 50 turns of wire 28 or thinner on a ferrite rod.
This circuit appears elsewhere on this site. Although the 8038 is not an easily obtainable...
The Texas Instruments TPS80 LDO (Low Dropout) series (www.ti.com) can provide fixed or adjustable output...
Found in Radio Electronics, this simple indicator circuit uses general-purpose transistors common today....