(note, this is a stub till I redraw some schematics to post with this)'
As an audiophool (in the past), I've long preferred solid state amps that are "a wire with gain" and will eventually get around to posting my improvements on the Dan Meyer "Tiger .01" circuit.
As a musician, I like tube amplifiers, mainly, as the job is different there -- you are producing, not reproducing sound, it's just a different game. My family (all engineers, some now deceased) were big tube buffs as well, so my first electronics were all tubes -- that was all there was when I began in the late '50's, after all. This eventually led to some pretty good "audiophool" class designs I will be sharing, the main goal of which was the old "wire with gain" standard, and the limitations were usually in the output iron -- then and now, things like UTC linear standard transformers don't grow on trees, and even those have issues and limitations, so I began to focus on how to overcome some of them.
The results were a couple of DC coupled tube amplifiers, right up to the transformer, long tailed differential throughout, with some feedforward compensation for the transformer characteristics. This was an interesting journey to say the least, as tubes do have some drift, and the "hard" low resistance transformer windings don't like DC imbalances, nor are they friendly to output tubes that decide to have a lower plate voltage than the supply -- things get hot! My first attempt, which a lot of people really liked, used two 12ax7's and two 6v6's as the outputs. All the "defects" like THD and IM distorion were below the (rather high) noise floor, and in tests, you couldn't tell which channel of a stereo amp had the crummy radio shack output iron, and which the linear standard, so it was a success by most measures. I will try and recreate the schematic from memory, as I gave it to a family member who since died and the people cleaning up the estate took it. So I won't remember all the resistor values and so on, just the basic wiring and ideas.
My other more recent attempt is sitting across the room for me, and was custom designed for a current tube-freak audio guy (he got the nice looking version, I kept the prototype). This one is audbily a tube amplifier, or as he says, sounds "tube-a-licious". I may have to pull it out and try it with my acoustic guitar at some point to see if it's any better than my excellent Fishman Loudbox (bi amped solid state, with nice features, the 8" woofer one that sounds better than their larger one). The customer insisted on triode outputs, which made it a lot harder to get in DC regulation, but eventually it worked, and we found some interesting things along the way. This one used nuvistors for the front end, then 6au6's for voltage gain, followed by the dual triode 3c33 for output. Doubtless few tube guys have even heard of this number -- it was low production right at the end of the tube era, used to drive mag amps for military servo/avionics things, but it's a decent size all-glass dual triode with nice curves, and I just happened to have about the world's supply of them on hand as new old stock. So, why not? Being exotic just gave better bragging rights to the eventual owner, which I suppose is important to someone paying that much for an audio amplifier.
Both of these designs were very unlike something Joe Sousa would normally do -- I didn't take any thought to making them minimal-component whatever, they were more "no holds barred" or "heroic" attempts to do the best at any cost or complexity, though they did come out simpler than some designs I've seen. Being DC coupled, both needed a lot of total supply voltage, which I got simply by making the usual full wave rectifier used in a tube amp into a bridge, to get plus and minus voltages. Further, I did DC supplies for all the tube filaments, to get rid of hum, which was largely successful. In general, most of the complexity actually wound up being in the power supplies, rather than the audio chain itself, since I needed some fairly good regulation on some odd voltages here and there to deal with the drifty tubes well. My only concession to solid state here was rectifiers, and in one case, a zener diode, but mostly I used the neat old gas tube regulators because hey, they are just cool and visually attractive. For the rest of the parts, the best available were used -- polypropylene or silver mica capacitors, 1% mil spec resistors and so forth -- that stuff is now cheap, and no reason to skimp when someone is crazy enough to pay you $10k/channel for a good amplifier, and yes, those guys exist (not many, though).
One of the interesting things we found (and Joe saw this during a vist here) was that the 7586 nuvistors I used as the first stage of the triode amp were temperature sensitive enough that touching one would cause a crazy amount of DC imbalance in the input stage. I wound up fabricating a custom "heat sink" that clamped over both tubes to keep them equal in temperature, a kind of 'tube integrated circuit" to deal with that, which had the side effect of looking pretty cool too, which again, is important at the rarified high end of audio-foolery. Being small, the response was fairly quick too -- a second or so, at this made me really do my homework so that there weren't conditions where one side dissipated more power than the other under normal conditions of audio inputs, a little bit of a challenge. The same issues appear in the article in this thread for solid state opamps, actually. The truth is, all these different technologies inform one another, and we all stand on the shoulders of the people who went before us. And it can sort of travel in time in either direction. Few were still working with tubes when that article was written, but the findings there informed more advanced tube designs just the same.
(I can see now I'm going to have to start another thread about tube amps for musicians, that have deliberate distortion and similar topics -- it's a lot of fun to play with changing the even and odd order distortion content on the fly in a design and in use. I am guessing that as my super video amp gets progress, it will go somewhere else, as it's not a legacy kind of thing, it's a modern thing where tubes just happen to be the best devices to use, still, since I need real high voltages at the output of that and without starting high, the magnetics problems become insurmountable.)
I'll get back here soon with some schematics of those amplifiers -- both turned out pretty well if you like that sort of thing. I'm not a very neat drawer of such things, but they should be readable, anyway. I don't think this should become "lost technology" which is the motivation here. You never know when the old will help out with the new, but I've been around the wheel a few times and it's happened enough to be worth paying attention to as a concept.