TO-18 metal can, 600 mA PNP switch
The 2N2907AL is a PNP switching transistor in a hermetically sealed TO-18 metal can — the package that dominated military and aerospace sockets for decades. Rated 600 mA continuous collector current and 60 V collector-emitter breakdown, it handles moderate loads in legacy and new designs where the metal can's reliability and thermal cycling tolerance beat plastic. The TO-18 (TO-206AA) three-lead can sits in a 0.230-inch diameter footprint with a 0.100-inch lead spacing — a direct drop-in for any board originally laid out for the 2N2907 family. The metal enclosure provides a hermetic seal against moisture and outgassing, making it a fit for sealed modules, avionics, and downhole instrumentation where plastic-packaged parts risk popcorn cracking.
Parametric ceiling — 500 mW at 200°C junction
Power dissipation is rated 500 mW at 25°C ambient, derating to zero at 200°C junction. For a 24 V rail switching a 150 mA relay coil, the transistor dissipates roughly 360 mW at saturation — within the 500 mW ceiling but leaving little margin for a hot enclosure. DC current gain (hFE) is guaranteed minimum 100 at 150 mA collector current with 10 V Vce — a solid beta for a general-purpose switch. The 1.6 V Vce(sat) at 50 mA base and 500 mA collector is the on-state voltage drop; at 500 mA the transistor dissipates 0.8 W in saturation, exceeding the 500 mW package limit unless pulsed or heatsunk.