So today I got a cheap Fender Pro Junior and I had some questions about tube amps. What do the two types of tubes do exactly? What function does the preamp serve and what does the power amp serve? It's got GT-12AX7 for the premp and Sovtek EL84 for the power amp. Are these good tubes? I would like a blues sound, so are these tubes what I need? A lot of noob questions but any answers would be appreciated.