I hate to say it, but now I think maybe I like my amp in ultralinear mode versus triode

Don’t feel bad about it. There’s some paranormal audiophile force that makes us feel like the more "purist" approach must always be better: triode versus pentode, DHT versus separate heaters, single-ended versus push-pull, ladder-dac versus delta-sigma, discrete circuitry versus opamp / IC, lower output MC versus higher, single full-range driver versus multiple etc. However, when we shut up and actually listen, we can plainly see this isn’t always the case - and certainly, preferences play their hand heavily here. And preferences can change over time - you’re allowed :)

I’ve done plenty of triode vs. UltraLinear comparisons on Rogue amps and prefer UL 9 times out of 10 (maybe more). Better dynamics and PRaT (or whatever you call it) for certain. I do play loud, and a lot of rock - certainly, that factors in. Triode has sweeter mids by a smidge, but it’s honestly so minor IMO. UL is awesome. Don’t confuse UL with "Pentode" mode. UL one of those rare compromises that leans very heavily into "best of both worlds" territory. It was hot sh*t when it was invented back in the 1940’s (!!), and still is. When I need a sweeter midrange (a common complaint in Rogue amps), rolling the right tubes moves the needle MUCH further than switching down to triode mode. That way I can get both dynamics, slam, and sweetness. The stock tubes can be fairly awful, honestly. I just put some Tung-Sol 7581A tubes in a Rogue ST100 I picked up for fun (office rig), threw away the stock JJ 12A*7’s (JJ’s go right in the trash), and holy crap this amp sounds amazing! Had a friend over to confirm. Yes, UL mode. I’ve owned Rogue's top-dog Apollo Darks before, own top-end VAC, and this little combo is somehow blowing me away right now.

I readily admit to how illiterate I am when it comes to electrical. Actually I had always thought that the one was a synonym for the other. I am in need of an education. Can you put into layman’s terms the difference between the three? If layman’s terms just won’t work because the subject matter is just too complex and it would take writing a book, I understand. I can live with just knowing that today I liked UL better today.

@immatthewj I’m no circuit analyst or electrical engineer, so I’m possibly not the guy you need to hear this from. But I’m a computer programmer who often has to explain things to people with a tenuous grasp of coding, so I’ll give it a crack lol. Based on my limited understanding, what differentiates a tetrode / pentode (call these both "pentode" from here on out, as the 5th element is not relevant to this discussion) from a triode is that the former have a screen grid that triodes don’t. The screen grid is positioned between the control/signal gird and the plate (the biggest metal part you see in a tube). You can sometimes spot it through the plate holes - its coiled wire is spaced out much more than the tighter control grid coils.

When you run these amps in "triode" mode, this screen is tied directly to the plate, and basically acts like it isn’t there (mostly). When you run them in "pentode" or UL mode, the screens are wired to the output transformers, but these 2 modes differ in exactly HOW they are wired to the transformer. Basically, UL is more cleverly done so that its distortion levels are much closer to triode mode than pentode (lower is better) and its power output is much closer to pentode mode than triode (higher is better). So you really do get "the best of both worlds", sort of. The output transformers do need to be designed with UL mode in mind for this to work. But frankly, it would be very odd to encounter an amplifier with only a "pentode" mode instead of UL (UL mode was devised in the 1930s and became common since the 1940s, e.g. the "Williamson" amplifier - incidentally, every time I hear of that "Wilsenton" Chinese amp brand I think that must be an Engrish-mangling of the name "Williamson"!). And those which offer switchable triode vs. "pentode" modes should also be rare - in those cases, you should probably just stick to triode. The only meaningful choice is triode versus UL. And in my opinion, borne out by when I’ve tried this - if you’ve got tetrode / pentode tubes running in your amps, you really want to be running UL mode. That’s the best use of their design elements.

True power triode tubes, DHT, and SingleEnded (these 3 often go together but not always!) are other balls of wax - I’ve heard them a couple times and don’t think they are for me. At least, I haven’t been won over yet. I listen loud and feel like I benefit too much from the extra power of UL mode. Give me tubes which slam, or give me solid state! (that’s better than death, I guess)

Everything was great at first then after a couple months the problems began, when I would turn everything on after a hour the amp would make the most awful load noises like metal bending and it was loud. That went on no matter what I would do,there was no support to help me…it was one of those things you could not find, then after a year or so the stock tubes started shorting out, getting that red light on start up, and fuses blowing at the same time…the wife and I would look at each other when I turned it on, holding our breath..the sound with the Fortes was ok not great

@silverfoxvtx1800 Ooof! I don’t know how on earth you had so much patience and/or capacity for self-abuse on that front! Months...a year later? I would’ve hit my tolerance limit at or before "a couple days" at most. If I thought my speakers were at risk it’s not going back on, period. And if the dealer / distributor / manufacturer aren’t willing to assist (sounds like a lemon unit), then frankly it’s going in the trash - and I'd let plenty of fellow audiophiles know what I think of said dealer / distrib / manufacturer. And then you say it didn’t even sound that great, to boot! Life is short man - find something else that brings you joy.

Isn’t ul mode solid State? Doesn’t it make sense that more would be involved for solid State and that it would sound a little bit

I think use of the word ultra linear is a marketing term and kind of dumb

Out of all the possible questions to be asked on this forum, this is one I would never have expected before now. No, UL is not solid state. And it’s about as much a marketing term as "gravity" or "electromagnetism".

Regardless of what we each think of the term "UltraLinear", and its alignment on the good-versus-evil spectrum, I found the following diagram most succinct and easy to digest. It’s from a web search that hits el34world dot com.

Note the wiring in the orange boxes (these would be easily controlled with switches), and the "UtraLinear" taps coming from the transformer primary, to the right - these UL taps are the legs that are positioned (symmetrically) between the 2 outer taps (each tied to their corresponding push/pull tube’s anode plate) and the center tap. These particular taps are disconnected in triode and pure pentode modes. They are connected to the corresponding tube screen grid in UL mode.

I assume the exact % of the UL taps’ positioning between outer taps and center tap is what’s at issue for "optimal" UL loading to a given output tube type - as circuit gurus like Ralph have pointed out.

In pentode mode, both tube screens are tied to the center tap. In triode mode, each screen is tied to its own tube's anode plate.