KT120 back to 6550


Seen a ton of threads praising the KT120 over the 6550 or KT88. I get the new tube's durability and design but given that your amp was originally designed around one of the older tubes has anybody gone back.

I recently purchased and ARC Ref 110 that came with a set of KT120s. The output tubes test and match well so they don't seem to be at the end of their life (same for the signal tubes). 

This was a change from a VT100 equipped with 6550s. The VT100 had good midrange but seemed a little lean otherwise. Percussion was fantastic and voices just right. Just deep bass a little thin. The REF 110 definitely fills in the deep bass but seem a little congested in the midrange. Both top and bottom are an improvement.

Both these amps were sandwiched between an LS25Mk1 and a pair of JBL 4430s. Could be a synergy thing, these speakers work very well with high power solid state (Adcom GFA 5802). I've been trying to work up a good tube amp for these but so far I'm not feeling the love.

So the question is could it just be this system would work better with 6550s instead of KT120s?

Thanks
monoogan

Showing 1 response by gbmcleod

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.