Válvulas e Guitarix

Preamp Tubes

• 12AX7: this is the main valve used in guitar preamps, famous for being used by Marshall (along with the inimitable EL34 on the power section) and VOX, producing (again with the EL34) the known “british sound”.
• 12AU7: A more modest valve (it only gives a 19% signal of a 12AX7), it was used in some vintage Gibson and Marshall amps.
• 12AT7
• 6DJ8: Also known in Europe as ECC88, it has an interesting tale to tell. It was first used in VHF tuners and later in many Hi-Fi amps of the time...

Power Tubes

• 6V6: “crystal-clear highs and powerful and defined bass” is what characterizes the “american sound” of Fender amps of the time. Nowadays their, bigger sibling 6L6 is used on the more powerful power stages.

Configurations

We can differentiate the sounds in: British sound (powerful mids), vintage (less saturated sound of 12AU7 and 6DJ8) and American sound (greater high and low end response by the 6V6). The remaining sounds of the 0.19 Guitarix version available in the SVN are a mix between them:

• Preamp + Power tube: 12AX7, 12AU7, 12AT7 or 6DJ8 + 6V6.
• Feedback config.
• Preamp + Push-pull power tube.

Feedback config is a positive feedback amp, adding a bit of gain.
Push-Pull amplifier is a Class AB power amp, allowing a higher output volume without too high peaks and adding some loudness to the mid level.

Fonte: https://sourceforge.net/p/guitarix/wiki/Tubes/