Good stuff up there form the Rivera site on tube descriptions. A couple are missing: 6V6 (Deluxe Reverb, etc.) and EL84 (Vox, etc.). More and more lately I'm interested in smaller amps (that happen to use these tubes), not just because of practicality, but because I love the tone of these valves.
Couldn't find a good decsription, but here's a start from the Boogie site:
"Both tubes have modest power handling capabilities of around 15 watts per pair. Both were widely used in the 1950s and '60s..."
"The 6V6 was widely used by Fender during the '50s and '60s for their low power models...Operating below the distortion threshold, the 6V6 sound is "skinny"-not objectionably thin, but bright nevertheless with bouncy, resilient dynamics. When overdriven, the low order second and third harmonics rise to predominance, obscuring the bright high frequencies and "fattening" the sound in a way which is a trademark of American blues."
"Meanwhile in Europe--particularly in England-during the same period, the EL84 was the power tube of choice in small amplifiers. The sound of this tube is very different from that of the 6V6. The EL84 possesses a glassy brightness whose emphasis is in frequencies higher than the bright zone of the 6V6...an aggressive, snarling bite..."