ver2 is in da house!!!
DO NOT POST REPLIES TO THIS THREAD!!
A quick introduction: Who is this guide for? (Plus a little bit of history...)
This guide was written with Average Audiophile Joe in mind. Simple(r) language was deliberately chosen in order to stay true to that aim. While some concepts explained within have been vastly simplified, I'm sure the purists out there will forgive me in view of my intended contribution towards the Greater Good.
To get the most out of this guide, it is best that you have some basic knowledge of physics and electrical concepts - basic atomic theory, electrical potential, resistance, capacitance, impedance, AC, DC, power transfer, transformers, rectification and other assorted ghouls will make their guest appearances within this guide.
If much of the previous paragraph resembled Cryptology 101, perhaps it is better that you take a gander over at Wikipedia (or a nearby library) to brush up on all the theory you slept through in high school.
The previous version of this guide not so much was a `guide' per se as it was a collection of links. While easy to set up, this left a little black spot on the author's conscience; like us, links frequently go dead suddenly - in my opinion a most unsatisfactory arrangement.
Setting aside a little time each day, I wrote this guide over 3 months. I hope you enjoy it and gain as much out of it as I did while writing it. 
-Aaron
-= Legend =-
Chapters are marked in
bold large red fonts.
Sections are marked in
bold underlined red font.
Sub-sections are marked in
bold and underlined font.
-= Contents =-
[click on chapter titles to go there directly]
[sections marked in red are incomplete]
1. ESSENTIAL KNOWLEDGE
1.1 What is a tube?
1.2 Tube types and general structure
1.3 A pictorial guide to tube structure
1.4 Tube naming conventions
1.5 Why tubes?
2. ADVANCED THEORY
2.1 Amplifier output stage topologies: SET vs Push-Pull vs OTL
2.2 Tube biasing
2.3 Regarding tube-based rectifiers…
2.4 Tube datasheets
2.5 Tube testers
2.6 The proper care and feeding of tubes
3. TIPS FOR THE SAVVY TUBE-MEISTER
3.1 What is 'tuberolling'?
3.2 Why do different tubes of the same type sound different?
3.3 What are NOS tubes?
3.4 USD$3000 for a single tube??! Why are some NOS tubes so expensive?!
3.5 Do NOS tubes really sound better?
3.6 Matched sections vs matched tubes
3.7 Buying and selling tubes
3.8 Relabeled tubes
3.9 Tube tweaks
+ + TUBE LINKS
+ + CREDITS & VERSION HISTORY