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

@mulveling , thank you for taking the time and effort to type out that explanation. I am going to print it and try reading it slowly and thoroughly to digest it. I think that you probably did a good job, I struggle with electrical. When I was in HS the Air Force recruiter told my mom that I did "real well on electrical on the ASVABs." I don’t believe that he was telling her the truth. When I finally did go in a year later, they were, "Sorry, son, electrical is full--how about open mechanical?" (Meaning airplane grease monkey.) Probably a good thing electrical was "filled up." I doubt I would have been good at it. Anyway, I think you are right about "better than death."

@atmasphere , thank you also for the explanations. I was pretty sure you would have a handle on this stuff. I now wish that I had gave UL a SERIOUS whirl (as opposed to the short try outs or ear bleed sessions) before this. Not that I didn’t like my amp in triode, but now I am thinking it is "more better sounding" in UL. Thanks again for the feed back.

UL mode is a pentode in "partial triode" mode. The screen and plate are operated at the same voltage and when the screen is tapped at the load (plate) it's triode mode and pentode mode when the screen is tapped at the B+ of the transformer. In between the two is the UL tap (about 40 to 43% of the winding) and that provides a negative feedback to the screen, resulting in lower distortion in push-pull operation.

I have a KT150 P-P. In UL mode it sounds like a solid state amp -- clean, tight transients and excellent bass response. In triode mode it's a little more syrupy and tube-like. I prefer the triode mode.

@gs5556 Your explanation is partially correct. The bit about 'partial triode' is not. What UL allows is for a pentode to have better linearity than a triode.

However there's been a wrinkle caused by the fact that the UL technology was the topic of a patent. To get around it, other manufacturers moved the taps away from the ideal point as taught by the patent. The linearity goes down rapidly. The patent also taught there was an ideal percentage for the tap that depended on the power tubes being used, which is why you can't use the same output transformer with EL34s and 6L6s unless there is a tap for each tube type.

The use of the incorrect tap has become a tradition and is now so ingrained that everyone thinks 40-43% is the right ratio; so UL operation it typically incorrect. I think that's part of why you see debate around 'UL vs triode' in high end audio. Depending on the amp, triode may or may not be better as a result. So its good in the case of the original post that the Cary seems to have gotten this bit right.

@ozzy62 , I will say that reading what the owner/operators of SETs have written about the experience has always sounded intriguing, if not tantalizing.  I sort of have a fantasy about higher efficiency speakers and one of Dennis Had's Inspire setups.  But that ship has sailed for now.  Maybe that is why I was so dead set locked in about triode versus UL--I thought it would be the next best thing?  Maybe.

@frogman your perception of triode versus UL is also interesting.  I suppose the possibility does exist that I am preferring UL at the moment in my sweet spot is due to it being different.  Different is often exciting.

@viridian 

It says right in your owners manual that the designer, Dennis Had, preferred the amp in triode, for whatever that is worth.

Yes it does!  And that may be where the power of suggestion comes in to play and why I was previously unwilling to give UP any serious time beyond ear-bleed rock-out sessions.  I also hate to admit that it was probably Dennis Had who turned me into a fan of Female vocalists.  The power of suggestion again.

@freediver 

I do however believe this is speaker dependent

possibly, and up until this spring I was always using the V12  in triode to drive a pair of B&W 805 Matrixes.  

@elliottbnewcombjr 

I remember a convesration we both particiapated in about someone's SLI80.  I believe you made a reference to face slapping when I stated I preferred my V12 in triode.

@silverfoxvtx1800 

wow!  I had a pair of ARC VTM120s that intermittently blew grid resistors on start up.  And I thought that was bad!  Those ARCs were pussy cats and replacing grid resistors was a minor inconvenience compared to what you just described.