SET, Tetrode, Pentode ?????

Can anyone explain the basic difference between single end triode;, pentode, tetrode, push-pull etc.and why I would want one versus the other?
Have been looking at EAR, BAT, VAC and VTL, all sound good , but have different designs/power, features.
Need some advise.
Those mainly have to do with the design of the output tubes. triode, pentode, tetrode, (diode?) all refer to the output tubes' types. It's rather complex, a good explanation is in the old RCA receiving tubes book, pick up one if you can find it, editions after about 1965-68 are the best.

Triode and Pentode are probably the best overall configurations. Pentode is about double the output power of triode, all else being equal. tetrode=not very common in high-end tube gear. single ended = one tube doing both pos. and neg. of the waveform. push-pull = one tube for each side of waveform. also other options like parallel single ended, transformer coupled, etc. Check in the tubes area, and FAQ for more info.

jim: here are a couple of primers on tubes, you may find informative:

keeping away from costly tubes in a power amp i might suggest a class A ss amp like a pass aleph design that easily performs like a tube set with far greater reliability! the class A aleph is single ended.
Thanks Cornfedboy, that is some interesting reading. Highly recommended!
As i understand it the single ended amps tend to be the low wattage midget amps that are used with the ultra high efficiency speakers. Never heard one but i hear the midrange is so killer it makes up for some weaknesses at the other extreams. Check out the VTL as they are switchable between triode and tetrode and each of those modes offer some advantages for different types of music. Sayas, i compared an aleph with an ARC VT100. Sadly, reliability issues aside, there was no comparison. The Aleph was great on it's own but the ARC walked away from it in top end smoothness and midrange in a side by side comparison. You're either a tube guy or you aint i guess.