Transister substitution

Looking for a substitute for 2SA818 and 2SC1628

Welcome to the Digikey tech forum. Take a look at Digikey part KSA940TU-ND as a possible alternate to 2SA818. The NPN complement is Digikey part KSC2073H2TU-ND as a possible alternate to 2SC1628. These are rated at 150v, be sure to verify the specs will work for your application.