Anax only likes the Woo WA5 and the Eddie Current amps with transformers.
My favorite Eddie Current amp doesn't have output transformers. The Zana Deux gets a nicely low output impedance from the 6C33C tubes. Their transformer-coupled amps are quite good, too, but the Zana is special because it is an OTL that drives low-impedance headphones well.
I'm not big on hybrids. Some are better than others, but quite a few are primarily solid state amps with a tube tacked on because everyone wants tube amps today.
The tipoff is when the list of acceptable tubes includes ones that are electrically incompatible. Some tubes can be swapped back and forth without changing the circuit, like the 12AX7 and the 5751. But amps that use multiple incompatible tubes have a switch, so the internal circuit changes for a different tube. You'll see this for amps that run the 2A3 and 45.
But if an amp claims to run multiple incompatible tubes without a switch, be careful. It means one of two things. First, it could mean that the amp has a sophisticated system that can detect a different tube, know what kind of tube it is, then automatically adjust itself. That's pretty unlikely. It'd be expensive and very complex - the kind of thing that would be bragged about in sales lit. It would be a real achievement since I don't know of any amp that does that.
On the other hand, the amp could be lighting up the filament (what makes a tube look like it is working) and then running multiple tubes
just enough to pass a signal and add some tube flavor to the solid state amp. Like a tube buffer.
Why not just run the tube as it was intended? There's a good reason for this. Tubes want a high voltage power supply. They start around 100V, but many like power in the 250V-400V range. That requires an expensive power transformer and some good filtering, also expensive.
Solid state runs on low voltage, around 12V-24V. That's a lot cheaper to build right.
So instead of having two power supplies, which would make the amp a lot more expensive, they run the tubes and solid state off the low voltage supply. You can get away with this because most tubes run 6V or 12V on the filaments. (You can tell by the first number of the tube's name: a 6SN7 has a 6V filament and a 12SL7 has a 12V filament). So the low power supply will make the tube look like it is working.
Then the tube is run at something like 12V so it'll pass the signal and add some tube flavor. But that tube won't really be amplifying the signal since, like I said, most will want 250V+ to really amplify, and it's too expensive to add a power supply that will do that.
The end result is primarily a solid state amp with a touch of tube coloration. Not really a real tube amp. It'd be like putting a teaspoon of scotch into a pint of water and telling people that it is a glass of scotch. These amps would work just fine if you bypassed their tubes.
Though I should add that some hybrids are legitimate and done right. But unless you can tease out the real thing from mostly a glass of water, be careful.
My take is to either run pure tubes or pure solid state. With pure tubes, you get a proper high voltage supply - there's no way to fake it. (Well, some put a switching power supply into amps. Those are electrically noisy, cheap and generally verboten in audio. Look it up. Good gear will run a linear power supply.) And don't dump on solid state. Done right it sounds fantastic. And you know there aren't any games played with it.
