extra cable

Hello. I am a regular in the small engines forum and am currently attending vo-tech school to be a diesel mechanic, which leads me to my question. I have been looking at generators for a long time and kind of understand the way to figure out how many watts I need but one thing I don't understand, especially about large industrial generators, what are hertz and duty cycles? Also, what is the difference between a single phase and a 3 phase? One other thing, if one day I get a small engine or a large diesel engine, where could I get the alternator head to bolt on to the engine? What companies make these alternators and how much would they cost? Thanks for the help.:D

I'm glad to have found this forum, as I am nearly out of ideas. I have a recessed lighting fixture in my basement that is nonfunctional. The fixture is 24 years old and I read that sometimes the cause is a 'flattened' contact tab, and to bend it out a bit. Well I did, and the tab broke. Thus I now must either 1) replace the socket or 2) replace the entire fixture. This of course assumes that the fault is not in the wiring, in which case there's even more work to be done. Towards this end I have a few questions: 1) The socket has two screws on either side of the bulb socket. Are these directly connected to the white & black wires that lead into the fixture? If so can i place a circuit tester on these two screws to determine whether electricity is flowing to the fixture? If the above is incorrect, how can I test to see if electricity is flowing to the fixture? 2) Can sockets in recessed fixtures generally be replaced without replacing the entire lighting fixture? Or, do i have to replace the whole thing? 3) Can recessed fixtures in a basement ceiling be replaced without cutting into the surrounding ceiling material? It seems the fixture is held in place via a series of metal tabs bent outward from the housing, so I'm not sure how I'm going to remove the fixture if indeed I need to replace the whole thing. Thanks to all who can lend a hand. -Randy