Hewwo. I am in need of buying a bunch of transistors and other components for some upcoming projects, but I do not know exactly how to recognize transistors. Are all NPN transistors alike? Are all PNP transistors alike? Do the numbers on the case mean alot or are they just model or make numbers? I know where I can get transistors, but I need to know if they are compatable with the ones I have/need. I would love to know for sure so I can get the correct kind of transistors. Thankies.