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

@decooney 

@immatthewj you were pretty close on your thoughts and memories of the Mesa Baron amp. Appears that amp delivers 150Wpc in full pentode mode, 120Wpc in 2/3 pentode, 85Wpc in 2/3 triode, and 60Wpc in full triode.

Ask: so, which of the switch modes did you enjoy most with the Mesa Baron amp?

If I may suggest, there might be a "next chapter" for you in your discovery, possibly moving to now try a (non-switchable) dedicated Ultralinear amp(s). Then trying a dedicated (non-strapped, true single ended) Triode amp with actual Triode tubes. 

I found that issue of Stereophile, and what a looker that amp was!  Dual monoblocks in one chassis, rack handles, meters, switches, knobs, a dozen output tubes . . . that, unfortunately, was probably a lot of the reason I was initially intrigued with it.  (A guy I used to work with used to say I was like the Indians who sold Manhattan for some shiny trinkets.  He may have been somewhat correct.)  Anyway, Anyway, I also found the flier from Mesa for The Baron that the dealer gave me (I had the flyer inside the Stereophile) and Mesa was saying that the amp utilized "pentode."  As far as which mode I preferred, well, I spent very little time in full triode or full pentode, most of the weekend was spent in 1/3 triode 2/3 pentode per dealer's advice, and I actually was intrigued and initially liked the presentation until I did the A/B I typed about.  At the time, I was using a B&K digital HT (prologic back then) preamp, and I had a dealer in Philadelphia who had set me up with that first system (the B&K and the SLA70) and I talked to him about the experience and maybe upgrading to a pair of SLM100s to get the sound stage without the "smokiness" and he told me (and I will have to paraphrase) that 'the Baron is a chameleon'  I do remember he did use the word "chameleon" and the sound I heard was due to the level of preamp.  Which may have been true.  But I didn't buy SLM100s from him.

What I did do not a whole lot later was to buy (through the classifieds in the back of Stereophile)  a secondhand pair of ARC VTM120s, four 6550s each, 100 wpc in NONSWITCHABLE UL.  And I like those ARCs, I really did; they would rock out (and I mean ROCK OUT) or whisper . . . and it was CLEAN sound and that was with the B&K in front.  And then, another aside, but still another local dealer had a second hand modded SLP90 that I took  home for a weekend, and then and there I learned the difference a preamp can make.

The reason I didn't keep those ARCs (I still have the SLA70, btw) is that they had a random habit of blowing a grid resistor on start up.  And taking one of them down and desoldering and resoldering grid resistors is no way to start a listening session.  I used to grit my teeth and cross my fingers when I flipped the switches.

Anyway, when Sterophile reviewed the V12 I was intrigued by the switchable from triode to UL feature and I knew that back then (in the Dennis Had/Kirk Owens days of Cary) I found my SLA70 to be reliable and Cary's tech support (when needed) was superb, so I took the plunge and bought a V12 from a dealer in Colorado, sight unseen.  

And that's how I got to the V12.

Thanks for the great post, and with your V12, did you roll any tubes besides the EL34s?  Like 6550s for example?  I do note that in the owner's manual, Dennis Had was saying one could do that.  I have about three good quads of 6550s for my SLA70 (six of NOS Tung Sols 6550 from Andy in Michigan, a quad of Svetlanta 6550Bs,  and I think a quad of KT88s, but I'd have to look to be sure, hat were branded "Tesla" that I got from Audio Advisor).  I was thinking of possibly biasing the amp for two tubes aside someday, and trying it in UL with 6550s?  I tried four tubes aside once back in '18 or '19, but I have to confess that this was back in the days when I was swearing by triode, and I wasn't crazy about it.

I was just pulling your leg. Its a bad habit I have.

@artemus_5 , you asked a legitimate question--I didn't take any offense to it.  After all the time I spent swearing that triode was a superior sound, I hated to admit that after yesterday I feel that I may have been mistaken.

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.

@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.