KT120 back to 6550

Lalitk, I believe the KT150 requires a higher draw, as such it can damage the transformer if that is not up to the task. Presumably, the transformer in the VT80 can handle the draw like in the VT80SE?

Very old thread, but I thought I’d add something I saw on the whatsbest forum site about the KT120s.
The poster (who has a 100k+ system) noticed that the KT120 were not "particularly transparent."
I would have to agree with that, having had them for months in my Audio Research Vsi60. The "sound" can impress you, but the actual transparency? It’s not, in my book, top of the world. And I say this as someone who once had a Goldmund Mimesis 9 (back in 1990), THE most transparent amp (although solid state) I have EVER had. NOTHING escaped its resolution. Terrific transparency, too. (It cost $11k back in 1990, so it would cost $23,000 (used an inflation calculator) in today’s dollars. I’ve heard some of today’s "super amps." The Goldmund only loses out in the bass frequencies, and some microdynamic nuances and delicacy.

Back to the KT 120s. The midrange is more "ice milk" than "ice cream." It CAN fool you because the resolution is good, but on stellar RCAs, Mercury Living Presence, Decca (all classical) of the ’50s and ’60s, the midrange does not have the lushness (and it’s there on the records). I’ve had Jadis, Goldmund, VTLs, VAC amplifiers, and Jadis, Convergent, Audio Research Sp-11, Rowland Coherence 1 preamplifiers (again, in the ’80s, ’90s, and into the new millenium) and none of them diluted the richness of tone that was on the album - if it was there to begin with. I think the (KT-120) midbass had punch and kick, BUT NOT the right amount of WEIGHT/BODY to make instruments solidify. And it is the midbass that is MAINLY responsible for the solidity of instrumental images, while the upper bass and lower midrange give the sound a kind of....well, lets use the words of Robert E. Greene, a former colleague at The Absolute Sound: " the power range" which makes music sound "BIG" when it swells up.

The KT-120s seem to have more ’push’ at the top and the bottom, but, after wondering if it was something else in my system (it wasn’t): I bought, over the last 2 years, top of the line Shunyata power cords (Sigmas), the Vsi60 (last year), Hana ML cartridge (last year), speakers (Nola), interconnects (two weeks ago) (jumped from Nordost Frey 2 to Nordost Tyr 2) and Shunyata Anaconda ZiTron speaker cables, I resigned myself to it being the sound of the KT-120s. Again, no component is perfect, so this is not meant to slam the tubes. I’m merely pointing out what I see? (hear?) as their inherent traits, so someone reading this can compares notes among all the posters here, many with equipment different than mine, and so the tubes will vary in other systems. Slightly. (The transparency factor, though? NO. That is a part of the tube itself.) But my comment is no more or less authoritative than anyone else’s. (It took me a while to come to the conclusion about its traits because I was changing equipment pretty rapidly over the last 7 months). The only things leftover from the previous system are the PS Audio Power Plant (and that never made anything sound thin), another (older) pair of Nola speakers, Shunyata Cobra ZiTron speaker cable and an Arcam FMJ23 CD player and that’s it. So, after hearing the tubes remain the same in terms of their virtues/flaws? It’s NOT my system!

If you have to "compensate" for sweetness - the kind that is in the music itself - than you’re adding a coloration to your system by getting something euphonic. No two ways about that. A truly neutral component will reveal "sweetness" if it’s already on the record. The component shouldn’t be doing it, because that’s a deviation from normal. And there’s no shame in building a system that way, but don’t kid yourself that your system is neutral if you do that. As soon as you upgrade/get some new component that is TRULY neutral, you’ll hear that euphonic component easily.

The KT-120s seem a bit "lightweight" in the midrange and also lacking in transparency. I can live with it, I guess. But I’m not happy about it. But glad I came here and saw that two posters noticed that "lightweight midrange" also. And I am comfortable with my experience as a listener of music through High End components over the past 40 years, since I bought close to state-of-the-art components (it speeded up my EDUCATION in High End components, for sure!), nor my time as a writer and editor in the high end industry.

I’m only writing this much print so someone else has an idea of what they might notice if they get these tubes. I like ’em, but not as much as some others. Oh, and the poster on the WhatsBest forum posited that the KT120s were not as transparent ( in the Vsi60) as the 6550 tubes, which, as it turns out, were the tubes installed in the amp when my old buddy, Wayne Garcia, wrote a review of the Vsi60 in The Absolute Sound. So, it would seem that with 6550s, you get the ultimate transparency; with the KT-120s, more slam and other qualities. Take your pick.

Worth bumping this thread again as this was a revelation to me and I think gbmcleod articulated what I heard very well.  I run Rogue M180 monoblocks with KT120 tubes and have a mature and highly resolving system, but was still lacking natural tone and transparency to vocals in particular.  Very detailed, layered and resolving, but not smooth, magical and perfectly clean and clear.  

Tested a matched set of new KT120s recently and while they were bigger, clearer and more layered, they still sounded somewhat the same.  Just newer and better.

Last night a friend stopped by as we have been discussing tube options (no surprise now) and he had picked up a set of 16 Svetlana winged C 6550 tubes for his ARC Classic 120s.  We dropped 8 into my M180s after level setting 3 album sides and were really impressed.  Lower noise floor and just such a perfect natural tone to vocals.  Nothing felt forced or had any edge.  More surprising was the bass just felt tighter as well.  Nothing bloomy like with the KT120s.

While certainly not a fair test of well used KT120s to NOS winged Cs, I did recently enough try new and matched KT120s to know I did not get the same transparent and involving experience, only better and similar to what I already had.  Makes sense.

Went back briefly to the KT120s last night before we all agreed, nope, put the winged Cs in for the rest of the night.  The pure transparency and natural tone of the winged Cs in my system was truly impressive.  One of the last albums I put on was the 45rpm 10 year year edition of Nicholas Jarr's Space is only Noise and it was pretty incredible.

Got about 6 hours of listening in before we had to pull them, but impressed enough to email my local tube guy at midnight and get a set of 8 6550 winged Cs ordered for me.  6550 tubes on my M180s?  I'm in. Who knew...

p.s. - To the OP, yes, I believe ARC switched to the KT120s when they ran out of said Svetlana winged C 6550 tubes specifically.  In fact, I think they had bought the bulk of them once they stopped being produced so they could run with them for as long as possible.   

 

@kingpin75s  I have heard the same thing as you on several amps, the 6550 sounded better. However, these amps were originally designed to run on 6550's and then modded to work with KT120's. Of the amps that were originally designed to work with KT120's, that is usually the best sounding tube for them. Was your amp originally designed ( circuit wise) to run 6550's?

@daveyf  Your observation makes sense.

Regarding:  Was your amp originally designed ( circuit wise) to run 6550's?

I would expect so as the original M120 monoblocks were based on 6550/EL34/KT88 tubes.