I think a lot of guys don't realize that tubes don't handle sound at all. They handle electrons! They are electrical devices, not acoustic.
Sound is converted into electricity to be fed into an amp. At the other end electricity is fed into a speaker, which moves air to transform the energy back into sound.
That means that tubes may have different gain factors but they are NOT going to colour the sound like different types of wood or strings in an acoustic guitar! Electrical signals are to sound waves as a photograph is to real flesh and blood. That is, you can have a representation but it it NOT the same thing!
That's why I don't buy into the idea that a different brand of 12AX7 might have "a greater midrange presence!" or some such malarkey. Tubes today are not built to the tight specs of the Golden Years so many brands have differing amounts of gain. That difference is what guys are hearing. You are not going to get a better bottom end from a different brand of tube. That tube amplifies from 0 to maybe a hundred MILLION cycles per second! To say that one has a bit more gain at 800 cycles or the midrange of an electric guitar is just silly.
That being said, there ARE overall quality differences! Some cheapo brands will turn microphonic very quickly, due to cheap internal construction. Some output tubes will handle higher plate voltages better than others. Tungsol 12AX7's DO have less hum, but they can't compensate for hum from a badly wired amp. Tone? Sorry, electrons don't have tone!
The gain factor can often mean everything. EL34's need much less drive than 6L6's. So do their little brothers, the EL84's. That's why they give that overdriven Marshall sound in essentially the same Bassman circuits.
6V6's fall in between a 6L6 and an El34 for sensitivity.
6550's are simply BIGGER 6L6's! Just as clean but you can get a lot more power out of 'em!
And as TG said, a different circuit with even the SAME tubes will sound very different! A Vox might use EL84's and so do many little Gibson amps but they don't sound anything alike. Their circuits are VERY different!
However, when you don't know how to change a circuit you can learn how, pay a tech or swap tubes around!
Learning takes time and effort. Techs cost money. Swapping tubes gives the illusion of making changes and really understanding what's going on.
To a tech, swapping tubes is like the difference between someone really playing guitar and someone dinking away with "Guitar Hero"!
Wild Bill, GuitarsCanada.com - The Canadian Guitar Forum - Powered by vBulletin
Yes, tubes are electrical devices. So are pickups, yet no one questions the fact pickups sound different. A 250 meg pot is an electronic device too, that also handles electrons, yet it has noticeably less high end than a 1k pot.
What this Wild Bill guy seems to forget is that an electric guitar changes vibrations into a flow of electrons, which then go into a guitar amp and are changed back into sound waves. He's just looking at the physics of it, and not looking very deeply at that either, and letting what he thinks should happen override what his ears are saying.
My experience has been that my Recto sounds seriously different with EL34s than with 6L6s, in ways that are abundantly obvious even in recorded clips, with the same exact circuit and same settings. They may "just handle electrons," but the way they handle them changes the sound you get when you convert those electrons back into sound energy in fundamental ways.