Found in a 1967 General Electric SCR manual, this circuit can be used to protect a load by switching in case of excess current. R1 determines the trigger current.
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....