Looking for advice on these speakers

If I may weigh in. . . There are SETs and then there are SETs; there are too many variables to lump all SETs together. I have Zu Def IVs and am happy with my Ancient Audio 300b SET (using Takatuski 300b) that seems to be able to drive these speakers successfully. (I have very eclectic tastes in music that include both solo instrument and fullscale orchestra, jazz, classic rock, female vocals, etc.) I started with a 45 SET and then tried a 2a3 SET; both sounded underpowered in my large space. I have also tried higher powered amplifiers, but was not impressed. On the other hand, Phil (213Cobra) swears by his Audion 845 SET with his Def IVs and his Audion 300b PSET with his Druid Vs and considers a 300b SET underpowered with insufficient drive for Zu speakers.

My post may be better suited for the amplifier forum, but since it is related to this discussion, I hope you'll indulge me.

My 180-watt tube monoblocks have a switch for ultralinear and triode operation. When I first got them a few years ago, I settled for the ultralinear mode and never thought to re-audition the decision, I guess since the mode was arguably the best compromise between low distortion and most power. This thread made me go back and revisit my choice and oh my. Perhaps there was something in the air today and it will disappear, but it was a revelation. The sound may have lost a fraction of the punch with rock music, but I just can't get over the overall improvement. Hard to describe it, but it's as if the sharp edges have been smoothed out, and a new quality to the sound emerged and made familiar recordings sound so revived and fresh they became literally intoxicating. In an A-B comparison, I could tell some difference, without a clear preference, leaning toward the triode mode, but not to the degree that the subsequent listening confirmed.

My amplifiers are obviously not SETs, but I'm curious to understand why switching to the triode operation made such a positive difference. Am I getting a taste of a true SET amplification with my 180-watt amps operating in the triode mode?

Hi,
I can relate to your revelatory experience. I had two Push pull amps that
were switchable between modes.
1) 40 watt UL and 20 watt triode.
2) 100watt UL and 60 watts triode.
In both of these amplifiers I much preferred the triode mode as the sound
was simply better/more natural IMO. It gets even better if you use true
triode tubes ( rather than pentodes strapped as triodes). I'm bias toward
DHT(directly heated triode) tubes which are very linear(and can get by with
little or no NFB added). When used in a SET or push pull configuration (if
good design and implementation) can further what you've described. It
must be emphasized that a proper speaker must
be chosen to extract the full potential sound that SETs are capble of.
I think you're headed in a good direction. The 300b is a very popular DHT (
but there's other good alternatives as well). My amp is SET, Al's VAC
Renaissance 70/70 is an excellent example of 300b push pull amplifier.
Just depends on what you want/need to drive your speakers.
As Gsm18439 alluded to, all SET amplifiers aren't created equal.
Once you find your desired amp-speaker combo I belive you'll be amazed
and very pleased.
Charles,

I'll second all of Charles' comments, and Gsm has provided some valuable perspectives as well, IMO. And although I've had no experience with Rogue products, yes I would suspect that going to triode mode on your 180's is shifting their sonics at least slightly in the SET direction.

I've had two amps that were switchable between the two modes, the classic and highly regarded vintage monoblock Marantz 2's and 9's, from the 1950's and 60's respectively, both of which I owned about 20 years ago. Both were EL34-based, with the 2's rated at about 20W/40W in the two modes, and the 9's at about 35W/70W. In both cases I much preferred the richer and in other ways subjectively better sonics of triode mode. Although the 20 watt triode mode capability of the 2's was inadequate on some recordings with the speakers I was using at the time, rated at 90 db/1W/1m and having fairly easy to drive impedance characteristics. In that mode with the 2's I actually caused the power tubes to arc and flash brightly a couple of times on Telarc bass drum beats, although no damage resulted. I don't recall having any problems with 40 watts.

BTW, a point of interest: In principle, if implemented in a certain way UL mode is capable of providing the sonic benefits of triode strapping, while providing considerably greater power capability at the same time. See this post by Atmasphere. You'll also find in that thread some varied reports of experiences comparing the two modes. As usual, implementation of the specific design seems to trump all.

Best,
-- Al

Al, I may have asked this question some time ago.

The output stage coupling of most ARC tube amps, at least my Ref 150, "is a combination of 'ultralinear' and Audio Research’s patented 'partially cathode-coupled' topology, which is superior to conventional pentode or triode operation." The foregoing cite is off of the ARCDB web site link to the Ref 150.

I have absolutely no idea what ARC is talking about, but suspect it may be a form of local negative feedback of sorts. ARC also touts that its circuit topology makes for better performance than "conventional pentode or triode operation." No comment.

I mention that here because of your last several posts which recommend caution in using some very low power SETs, especially if the amp will be called upon to drive dynamic music. Certainly, there are higher power amp options that may get one close to the presumed benefits of a SET amp, e.g., Ralph's zero NF OTL amps, or VAC amps, etc.

Maybe you can push the fog away.