sub's right. If i may add, pre-amp tubes for me are the ones shaping your overall tone(dark, bright, middy, less middy, smooth, throaty, etc.) while power amp tubes tends to lean more on giving the amp its feel(early brake up, late break up) .Though power amp tubes will also contribute to some tone shaping like the bassy-ness or middy-ness of an amp, they are not as dominant as the pre-amp tubes.
I have an experience with comparing el34 and 6L6 power tube amps, while I can say 6L6 tubes are way bassier, I think on a live context the audience won't be able to tell what kind of power tubes amp are you using. But you will feel whether the tube amp is spongy or stiff in response.
I know some guys would say that el34 sounds marshally and 6L6 are fendery but IMHO, what they are hearing are the circuits where these power tubes are commonly used. Even if you interchange them(with some biasing involved), your fender amp will still be a fender-sounding amp and same goes for marshalls.