I've seen people saying the preamp tubes is all that matters to them, so i'd like to know some opinions about it
Most of the true tube aficionados believe the real magic occurs in the output section. Something to keep in mind is they like to push the amp up to edge where the output section is on the verge of crossing over into distortion. At this point what happens with most tube amps is the sound compresses quite a bit, the tone will thicken and the feel slows a bit, and you might get a bit of touch sensitive distortion. I actually have a bunch of tube amps, but in general I like to avoid this condition, so I guess at heart I am really a solid state guy.
Another difference you may be interested in is preamps use single ended amplifier sections and most all-tube bass amps use push-pull output sections. When pushed into distortion, single ended circuits and push-pull circuits tend to produce a different harmonic series, so they sound different.
Another factor is the output section taxes the power supply much heavier than the preamp. So when you push the output tubes hard, they will pull the supply voltage down. This is where some of the compression comes from. I believe it also widens the transition/envelope from where the amp crosses from clean and punchy, to compression, to light OD, to heavy distortion. In my experience, hybrids with a tube preamps typically have a narrow envelope, so it is a bit harder to stay in the sweet spot without using some additional compression.
You also need to understand that there are many different tube amp designs that can sound drastically different from one another, Ampegs and Hiwatts for example incite tribal loyalties among the faithful. I own multiples of each and think they are awesome, but sound and feel very different from one another.
Also when people talk about "tubey goodness," be aware that the term may mean very different things to different people. There are lot's of characteristics that people consider tubey, and IMHO some of them are just outright inaccurate. For example, warm is a common term use to describe tubey goodness, but in my experience most tube amps are actually voiced significantly brighter than most solid state amps. The warm tone comes from the type of speaker used with the amp; not the tubes. Tube aficionados tend to prefer traditional speakers like 810s or 215s that do not have tweeters. Many of these traditional speakers roll of high frequencies, so you get a nice warm tone even if the amp is voiced rather brightly. Play a Hiwatt through a nice full range flat response cab and you'll get the idea very quickly about how bright the amps are voiced. Ampegs on the other hand are relatively flat.
This thread should degrade fairly quickly into a tube versus solid state thread; which typically happens every couple of weeks or so. Honestly I don't there is much to learn from reading about anyone else's preference. You need to try a bunch of amps and find out what you like. What I like is totally irrelevant to your journey, but I own several solid state, hybrid, and all-tube amps, so I tend to keep an open mind on these matter instead of going tribal.
Good luck.
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