Piggybacking off what Giannifive
is saying yes. The Preamp is where most of your tone shaping comes from. In a fairly typical setup your gain/vol I/pre, bass, mid, treble knobs are controlling your preamp sound. The power amp really does the heavy lifting and takes the sound of the preamp and boosts that sucker up to some real volumes. The power amp can have some tone shaping controls of its own, obviously the master/vol II/post being on most any design after the 60's but there can also be a resonance (adjusts bass frequencies) and presence (adjusting treble frequencies) to further refine the sound.
The main advantage in tube pre/SS power amps is in the classic fender clean to mid/classic gain range; excelling in warmer tones and sounds than a lot of all SS/digital designs. These are becoming less popular as digital stuff has made leaps and bounds in these areas in the last decade.
The ss/digital pre/tube power amps are becoming more popular these days (read: Line 6 Spider Valve) because of the chameleon like versatility to go from SUPER clean sounds all the way up to mega metal compressed gain while not getting mushy. The tube power amp in an amp like the spider valve helps address the problem so many guitarists have had in the past when they crank up their SS/digital amp, they sound BAD. Since the sound characteristics of SS poweramps stay relatively static they are often accused of being stale, sterile and lifeless. Some have welcomed the stiff tightness and icepick high end, namely extreme metal guitarists. The other issue is when SS power amps get turned up past their rated range they completely fail and start to produce a sound similar to a blown speaker but worse. This is why you'll see a 300 watt SS/Digital amp compared next to a 100 watt tube amp, no one wants to get near that harsh mess of a sound. The spider valve fixes all that with the gentle compression and bloom dynamics of it's tube power amp. At higher volumes the treble has a more natural roll off and the low end while not quite as tight can be a bit more bombastic with a little rumble to it.
All-tube amp designs takes the compression/bloom concept and cranks up the dynamics even more so. Even within the designation of "all-tube" which is usually defined as both pre and power amp being tube driven there are amps with solid state rectifiers (usually high gain amps) and tube rectifiers (typically low-mid gain combos) that keep the amps response relatively tight (SS) or with even more sag/compression/bloom (tube) The Mesa Boogie Dual Rectifier is named so because it has the ability to do both. There's also class A/B designs (Marshall JCM, Mesa Recto) that are known for bigger volume and bolder tones (generally 50w and higher) versus Class A designs that display a generally sweeter tone with lower power (generally under 50w with a few exceptions). There's even more once you get WAY into it but that's kind of the crash course. Other than the superb dynamics, tube amps have a very full sounding character to their tones, this is especially noticeable when doing an back to back comparison with an all SS/Digital amp at moderate to loud volumes. Tube amps are heavy, expensive and all around inconvenient but damn do they sound and feel AMAZING. Digital is getting better and better as we speak so who knows what'll happen next but I think there will always be a few stubborn purists who prefer a cranked half stack or combo to a computer plugged into a P.A. system.
Sorry for writing a novel