Tube Newbie question

Thanks so much for your articulate responses. You've given me a great place to start.

Nathan

find a dealer or supplier with whom you can build a relationship with. this person can serve as a mentor until you develop your own experience and knowledge base...it's what many of us have done, myself included. other posters comments are also valid but find a tube source (I don't mean Ebay) and work from there.
welcome to the world of tubes....
Larry

One of the best introductions I have ever seen to the world of valve amplification can be found here - "A Taste of Tubes":

http://www.anthemav.com/OldSitev1/pdf/taste.pdf

There are very detailed explanations of the sonic characteristics of various tubes (and they are grouped by tube equivalent) in Joe's Tube Lore at Audio Asylum.

Tubes are a complex issue. The best thing for a newcomer to do is to not use a tube in a circuit unless the manufacturer has OK'd it in their manual or it is known to be an acceptable direct substitute. (For example, the EL84 and 6BQ5 are the same tube (European designation vs American.)

Different brands of the same type tube may sound different, but they are supposed to safely substitute for one another without issue.

There are also near substitutes that can be used by more knowledgeable people, but these may require an amp to be rebiased or even have a part or two changed.

Tubes do wear out, but only from active use. An usused tube can sit on a shelf for 25 or 50 years and be as good as the day it was made if not physically damaged. That is why there is an active trade in NOS (new old stock) tubes.

A power output tube on an amp may last 1,500 to 2,000 hours while a preamp tube may last 10,000 hours or more. Circuit design can lengthen or shorten these times. (Think of an auto tire. The same tire will wear faster on a heavier car than a lighter one, even if they are driven in the same fashion.) Tube electronics also throw a lot of heat so need to be well-ventilated. Poor ventilation can shorten tube life (as well as other components in the equipment.)