Found in a 1964 Electronic Design, this circuit generates pulses based on an avalanche diode of the time. The circuit can be tested with modern equivalent components.
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....