I understand that the gain will not be the same at all voltages, and all currents, but the part is pretty limited in its rage of current, and using it at 5v is very common (especially when you are using it with microcontroller, like we do on this forum)
With a 2n2222 transistor, and 5v, how many possible base resistor sizes could I need? We know the current wont be more than 1/2 amp, or we would need a different transistor. At 240ma, you may have a different gain than at 10ma, which will effect the size of the base resistor. but at similar current levels, it should be pretty similar (note: similar does not mean exactly the same, it means near, or close to.) I understand there will be some deviation from lot to lot, and manufacturer to manufacturer but at 5v, one size resistor should be good for a fair range of current.
Anyway doing the calculations isnt the problem, calculating my needs isnt a problem, figuring out the right value for gain/beta/hfe is a problem You mentioned that I can assume its 50, someone else says I should assume its 10, another person says its probably about 100.
When all is said and done, the calculations were kind of pointless, since I had to hook them up and measure to find the answer.
Moderator edit: severe over-quoting removed; vitriol removed