TO-18 metal can — through-hole workhorse
The 2N2907AE4 is a PNP general-purpose switching transistor in the classic TO-18 (TO-206AA) metal can package. It handles up to 600 mA collector current and 60 V collector-emitter breakdown, with a maximum power dissipation of 500 mW. The metal can gives you a hermetic seal and a rugged lead frame — good for environments where plastic packages might crack or outgas. The through-hole leads are breadboard-friendly and easy to hand-solder, so it's a natural pick for prototyping or one-off builds.
DC gain and saturation — what the numbers mean for your circuit
That means at 150 mA you get at least 100× current amplification — enough to drive a relay or a small motor from a logic-level base signal without needing a Darlington pair. Vce saturation is specified at 1.6 V max with 50 mA base current driving 500 mA collector current. The 1.6 V drop at 500 mA means about 800 mW of conduction loss inside the transistor — within the 500 mW package limit only if you pulse it or keep duty cycle low. For continuous 500 mA you'd want a heatsink or a larger package. Collector cutoff current is just 50 nA max — that's negligible leakage, so it won't pull your load when the base is grounded. The operating temperature range of -65°C to 200°C covers military and industrial extremes, from cold-soak avionics to hot engine bays.