The BC 846B E6433: NPN transistor in a surface-mount SOT-23-3 package. Rated for 65 V Vceo, 100 mA Ic, 250 MHz ft.
The 65 V Vceo breakdown is the headline selection parameter — it comfortably covers 24 V and 48 V industrial buses with derating headroom, but it is not a 100 V part, so a 60 V nominal rail would leave no margin. The 100 mA continuous collector current is the DC limit; pulse currents can exceed this, but the 330 mW maximum power dissipation in the SOT-23 footprint is the real thermal constraint. At 25 °C ambient, 330 mW translates to roughly 110 mA at 3 V Vce — above that, junction temperature climbs toward the 150 °C(TJ) maximum. The 250 MHz transition frequency is high enough for low-frequency switching and audio-band amplification but not for RF front-end work above 100 MHz.
No official successor listed. For dual-sourcing or a drop-in replacement, the base product number BC 846 covers multiple gain selections and package variants.