What's the tonal difference between the most common tubes (6L6, 6V6, EL84)? Any good soundclips on the 'net that illustrate this?
6L6 - Most headroom (as well as wattage potential) of the three. Most bass response and most piercing and least-compressed treble range. Also has the most recessed midrange response of most any tube. It's more oriented toward very solid clean tones, though it can overdrive with great character too.
6V6 - More midrange emphasis than 6L6, with considerably less headroom too. It has a less compressed midrange character, in general, than el84 tubes, as well as, more low-midrange than el84's. 6V6 tubes overdrive with a harder midrange edge than el84 tubes. And, 6V6's have a very pleasant high-end, with just enough compression. This tube, along with KT66 and EL34 tubes, produces some of the greatest overdrive tones possible IMO.
el84 - Has the most high-midrange emphasis, which creates it's very characteristic chime in almost any circuit, which is not readily EQ'd out. It's the Vox-type chime. The overdrive tone can be quite compressed - it is not as hard a crunch as 6V6 - it's considerably softer. Some love this, some don't like it at all. It can produce some very characterful and chimey clean (bordering on crunch) tones - that's what it does best IMO.
Max plate dissipations(in tetrode connection):I heard that the 5881 is a good sounding tube in place of a 6L6. I was told alittle less power than a 6L6 but can develop a nice clean and overdrive tones. I haven't tried the 5881. Perhaps someone can comment on the virtues of that tube.