@daveyf these are the QS Mono 120s are 120watt amps designed and sold with KT150s new as stock. KT120s are doable yet I cannot run KT88s or EL34s in these amps. Will burn them up, according to the designer. These have the big transformers and power caps in these particular amps, very transparent too.. They do run higher plate voltage in these. KT150s are super linear in these amps. I sort yearn for a throwback KT88 type sound every once in a while, so the KT120s put me back closer to that when I swap them in. KT150s and KT120s only in these. Already had quad spares thank goodness.
KT150 to KT120..or KT120 to KT150
Has anyone here gone from using KT120's in their amp to KT150's and preferred the KT150 tube...conversely has anyone gone from KT150's in their amp to KT120's and preferred the KT120's?
Showing 22 responses by decooney
Check with the amp designer if you can before buying KT150s, fwiw. Test-1: In reverse, just for grins I tried KT120s in my monoblock amps specifically designed and optimized to run KT150s. Day-1 the amps were designed to run KT150s, big transformers, increase in plate voltage, etc. The KT120s were a bit more dry sounding, not as musical, bass was less full in THESE particular amps. Re-installed the KT150s and wallah, nice! Was it too much plate voltage, too much bias, or a less optimum circuit for the KT120s, possibly. --------------------- Test-2: A buddy had tried KT150s in his nice upgraded integrated amp originally designed to run KT88s. He’d been complaining it did not sound right to him. We popped in some new production PAVANE CV-181s, wallah, nice! Was it due to an insufficient amount of plate voltage, smaller transformers, an amp never designed to run KT150s, possibly. ----------------------- If unsure, defer to the amp designer about "what output tubes" to run. | |
@dsholl1 I’m a big EL34 amp fan myself in the right implementation. Was hopeful the KT120 would be the answer, for the exact same reasons you’ve outlined here - however MY particular amps just did okay with them. The amp designer told me to try KT120s knowing I was a big EL34 fan, but we eventually agreed the KT150 was a better synergy in my case. New, yes, at first the KT150s had more of a "hi fi sound", yet at 200-300 hours run-in time on the KT150s output tubes + good vintage input/driver (12xx7), was a game changer. More of an EL34 sound now with a tad more air on top and definitely more weight on the bottom-end, less rounded off on the bottom end now - with THESE amps. >> the real trick I found was getting the right vintage input tubes paired with KT150 output tubes to achieve the right balance, tone, texture << Pairing the good input tubes and the right silver-gold coupling caps in my amps truly made the KT150s a real pleasure to listen to now. Not until then. I’ve also heard the same amps with stock caps and stock input tubes with 500+ hours on the KT150s and they smoothed waaaaay out. KT150s do smooth down with longer run-in time. | |
@daveyf Yes, and...With limited availability and great variation in supply in large scale, it seems many tube amp designers kinda have no choice but to focus more on new tubes now, and much discussion about Vintage input/driver tubes ends abruptly - for good reason. I.e “why talk about it if it’s not something they can do with consistency” etc. Or the rare few with a massive supply stash of NOS at a special price for purchase with new amps 😳 I find the same abrupt conversation occurs with average vs high quality coupling caps replacement. Most just go with the available average stuff to keep cost under control (and keep variation down to standardize) as it seems; excluding the few builders that offer “upgrades” as an option with warranty. It’s great to see some of the better designers able to voice some of these recent version amps with the newer tubes over the past few years. Some of the latest builds with KT150s are starting to sound really nice. Keeps it interesting. Quite a few more amps out with KT150s this past year, still evolving it seems. Good fun. | |
Found a helpful article for anyone comparing the jump from EL34 to KT150 output tube based amplifiers. My former amps were EL34 output tube based. Liked them fairly well. Loved the midrange. Now running other new mono tube amps, jumped through KT120s, on to KT150s, not letting myself forget the former, EL34s.. Initially, I missed my old amp and the magical EL34s, until the KT150s got past 150hrs burn-in. Also, found the right pair of small input/drive tubes to pair up, thus changing the sound of the KT150 result in a great way. After burn-in, soon realized I did not miss the EL34s or KT120s any more. Article, Hifi-Advice: See the "From EL34 to KT150" or "From KT150 to EL34" paragraphs. A helpful read to confirm what I've been hearing, even with completely different amps yet experiencing similar findings after making the jump. https://www.hifi-advice.com/blog/review/analog-reviews/amplifier-reviews/primaluna-dialogue-premium-... | |
@daveyf if I learned anything more since this thread, its back to what a few mentors have shared with me, it's about the designer and the circuit... If the amp was optimized to sound a particular way with a certain input or output tube (in this case), merely changing output tubes up the chain might not necessarily improve the sound. Also, I've been varying bias on my own KT150s between 40,45,50,55 ma in my mono amps. While I could not get the KT120s to sound quite right in my particular amps, trying different bias has changed the sound, tone, sound stage and character of the presentation to keep it interesting and enjoyable to listen to. Back down to 40ma now and a tad more laid back, less forward, which I tend to prefer in my particular system and speakers. | |
@fsonicsmith Does your ARC 150 amp have the upgraded and lowered main circuit board mod for KT150s, and with more clearance for the top cover? I remember reading some (not all) of the ARC tube amps around 2015 having issues with KT150s and main board changes, some failing resistors or something, among other things got redesigned. Bias issue and close matching tubes might not be as much of an issue after mod, I don't know. Also, comments about improved sonic quality and longevity. Seeing redesigned amps by different brands with KT150s past two years, and suspecting maybe they figured out how to drive the tubes differently, fwiw. I wonder if ARC might offer any tweaks for them today? | |
@daveyf Good to know. I have some friends with CJ older amps that swear the KT120 sounds better in THEIR particular amps, i.e. not designed to run KT150s. I believe what your designer friend is saying maybe for that amp circuit. Fast forward, now CJ has amps designed for KT150s, 2x the cost, go figure. Optimized to run KT150s. All new amps, new circuits... In reverse, my current mono tube amps are designed to run KT150s natively, but I thought I'd be smart and try KT120s at first hoping they'd sound more like EL34s did in my old amps. Amp designer said I could try KT120s and see. Nope, no-go. They sounded more dry, less musical, kinda plain, some call it analytical, less musical - and lost some air up top. Just not engaging in these amps. Yanked the KT120s and replaced with matched pairs of KT150s, and wallah (for these amps). More top air, more bottom, and a mild mannered midrange. So, I then ended up back to rotating the former pairs of vintage input/drivers in my amps to bring out more midrange, it was better. Then, went to better coupling caps, and even better midrange with KT150s, now I was "there". When I tried these same changes with KT120s, just did not help all that much. With KT150s, worked really well. And, opposite in my buddies integrated amp that was originally designed and voiced for KT88s. The new KT150s were not cutting it in HIS amps. Less musical. Yanked out KT150s after 6 months, then went with PSVANE KT88s, and wow they worked so much better in HIS amp. Finding the right tube(s) inpu/driver/output for the circuit seems to be the ticket for me. I don't know if I believe in the whole "universal" amp theory and just changing the driver.. may work with some combos, not all. My designer knew KT150s worked better in my amps circuit. | |
@wolf_garcia On that note, KT150s were not particularly special in my former SEP Class A DH Inspire Hot Rod amp either. Seems most like the smaller tubes with the smaller transformers in that amp. I concluded that KT150 tubes were a waste of $ and no value-add in those smaller footprint amps. However, KT150s in my current Quicksilver Mono 120 tube amps is at an entirely different level of sound, stage, and enjoyment for sure. Transformers are 2.5x the size, higher plate voltage used, and yet I can manually bias them down to about 40ma per tube, and it sounds closer to something between EL34 and KT88s in triode mode in my prior Cary or Inspire amps. Owners stating something similar about the higher $ CJ amps specifically designed for KT150s. Seems the specific amp design, the circuit, and use of sizable transformers sure make a difference for running KT150 tubes in their most optimum state. Now seeing more amps designed just for KT150s. | |
1/8/2022: KT150 > KT120s. Re-testing and giving it a lot more time this go-around with two mono amplifiers specifically designed to run KT120s and KT150s. Big transformers, higher plate voltage, 40-45ma per tube bias. Picked up a quad of Tung Sol KT120s a week ago. Giving it another try after locating and reading back through threads I’d not seen before on the CJ Owners Forum and DIY builders, noting several members favoring KT120s over KT150s and KT88s. I kept seeing these comments, and realized it was time for a complete do-over. Update; At 48hrs burn-in on the KT120s, here is what I’m noticing in comparison to KT150s. After more time and paying close attention, I’m observing similar traits as others. The KT120s vs. KT150s, are:
Adding to the thread, hope it helps others. I’ve come to appreciate the KT120s a lot more than I did the first time around. They are a nice [go-between] alternative to KT88s or the more clear and linear sounding KT150s. | |
runwell, I agree with your comments and description. The plan is to rotate the KT150s back in every once in a while. They are an amazing wide range tube with added depth, clarity, sound stage. Definitely in a class of their own, yes, agree. However, the KT120s are a "throwback" to older familiar tube sounds I use to enjoy and expect from all of my former tube amplifiers with el34s, kt88. A nice tradeoff too. I understand >> a lot better now << what some were reporting about why they liked or preferred KT120s over KT150s. There are different reasons I like and appreciate both - particularly when used with purpose built amplifiers designed to run them. | |
[Initial burn-in matters on these tubes]. I underestimated this on the first try.
KT150s: AFTER 200hrs of play, I now consider the KT150 as a sort of a "do no harm" output tube in my mono block amplifiers. Brand new, I did not like them very much. Way better after 200-300hrs. I had been comparing back and forth with my audio local dealer too in the same amps. Top end smoothed more at 300hrs, wearing in. KT120s: In similar fashion, I did not like them brand new in the first 24-48hrs. In fact, I passed over them too quickly jumping to KT150s prematurely. Missing velvety texture, tone, gave them another shot and super glad I did. At 72hrs+ started showing some hope with a tad rolled off highs/lows. Nice though. Easy listening. | |
[Interconnect type pairing between these two output tubes] can help fine tone too. If you trying both of these types of OTs, and you are looking for fine tuning of tone and prefer a good balance half way between ultra clear and rich tones, here are two combinations I landed on with interconnects after a few hundred hours of comparative testing fwiw. I don’t run silver over copper interconnects any more except with EL34 output tubes. This is only referring to KT120 vs. KT150s in neutral sounding amplifiers. Your results may vary of course. Happy listening.
KT150 / OFC ICs:
KT120 / OCC ICs:
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daveyf OP
Sure, and referring to tone changes mostly in a specific case example as an approach. No debate on whether OCCs work well or not with KT150s. All preference. In fact, I’m running Analysis Plus Crystal OCC cables at my source to preamp, preamp to amps right now with (KT120s or KT150s). Also, validated with five different pairs of Cardas Audio interconnect cables too up and down the line, in a similar manner. If I change to the exact same design cables in OFC Copper, it offers a slightly richer tone at the cost of slight loss of upper most frequency detail. Something else to try in general terms with tube comparisons, if interested.
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@daveyf my KT150s are back in their boxes, nice, yet kept comparing. After the KT120s had 100-200hrs on them, have not wanted to remove them. My first impressions were off for sure, and they just needed time to settle in. Very nice. | |
@daveyf two Quicksilver Mono 120 tube amplifiers with upgraded Mundorf EVO Silver Gold (non oil) capacitors, Premium Psvane MKII 12AU7 and 12AT7 small signal tubes paired with Tung Sol KT120 output tubes. Combo works nicely. | |
@daveyf, I had a Dennis Had Inspire KT150 Hot Rod amp for a year. Was nice, fairly resolving, yet I needed more than 10wpc for my larger 92.5 db amt/ribbon speakers. And was sure the 150 tube could do more with more transformer and plate voltage behind it. Sure enough, two years later ended up with the QS Mono 120 with KT150s. Wow, much fuller, bolder midrange, super transparent, hearing deep in to the sound stage, across the front. Now he and crew are fascinated with KT170s. A good sign. Glad to see other new tubes coming out. Would be nice to see WE do something less exotic and more mainstream. Meanwhile I'm going backwards landing on a blend of old/new sound. Nice. | |
-------------------------------------------------------------- @ozzy for what its worth to you, while my purpose built mono block tube amps were designed specifically to run KT150s, nice, clear, pure, I am back to running KT120s again, now. Kinda missed the more textured (older) midrange, so I’ve alternated a few times. 150s are extra detailed on top, slightly larger and deeper sound stage if bias is turned up, but is the grass greener, maybe. The 150s can be so linear sometimes on my system, i miss that littlest of the midrange bulge reminiscent of EL34s, KT77s and maybe even KT88s. Popped the 120s back in, and there it is. Back and forth enough times now to know for sure in my setup. Been playing again with bias on both 120s and 150s past six months. On my amps both tubes at 60ma are brighter. My ears are sensitive to bright sound. After 100-200hrs+ on both KT150s or KT120s, I decided on backing the bias down to 40-45ma per tube for low volume listening. Normally at 50ma. Just for grins, now sitting at 40ma with KT120s, lowest I’ll go. #1) saves the tubes a little longer, #2) takes a little of top edge off with bad recordings, and sounds nice. No fatigue at all. Save the $, keep enjoying those KT120s! I have zero desire to put the KT150s back in, and not for a good while. Like them enough that I had a spare quad set of KT120s stored too. | |
@jerryg123 are you running your KT170s in amps with proper transformers and plate voltage ability to take advantage of the extra 15 watts capability these tubes have over the KT150s? What "attributes" are you hearing differently from KT150s - if you can share more, thanks. | |
Thanks @jerryg123 that helps understand more.Similar findings excluding 170s. I've owned and listened to a few amps running KT150s with smaller transformers and lower plate voltage, and they did not sound very good to me. KT88s were nicer in amps designed for the smaller and lower power tubes. While my amps were designed for KT150s, and they sound unique vs. other smaller amps I've run KT150s in before, I have yet to hear a robust amp specifically designed for KT170s to get the most out of them. Doing some research, came across a designer noting this about them: "The Tung-Sol KT170 has a plate dissipation of 85 watts! ... making it the most powerful tube in the Tung-Sol family. A pair of these tubes in push-pull configuration can deliver power levels of 190 or more watts. When used at the parameters found in existing 6550/KT88/KT90 circuits, the Tung-Sol KT170 is impervious to overload, delivering peak power with extreme reliability and long tube life. However, taking advantage of the higher current handling capacity of these tubes, a very unique and super powerful and stable amp can be designed using the Tung-Sol KT-170." unquote. Hopefully other future manufacturers will come out with their own competitive versions of KT150s and KT170s to try. Will be on the lookout.
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@wolf_garcia Nice, good for you. The 25 is a nice amp. Except for a signature 98 preamp, I sold off most of my DH, Cary, and Inspire stuff. Was nice, gone now. Moved on. I’m following along with few buddies considering going back to ss myself after hoarding enough collections of tubes. In two years, maybe taking a step in reverse further backwards to a full integrated, pass or coda. Enjoying tube monos a few more years or while it lasts. Enjoy the xa25, nice with the right preamp. | |
@aljordan I now run between 45-50ma with the KT120s in the Mono 120 amplifiers. There is a difference, the Mono 120s have a plate voltage of 600v at the plate. Running the basic calculators, it says I’m barely close to running the KT120s in their optimum window. Don’t recall if Silver 88s run 450v at the plate or what. Not near a place I can check but would be good to find out what plate voltage your amps are, and check a calc to see what is optimum current for yours, amps, tubes when running KT88 or KT120 or KT150. Yes, you’ll get less high freq extension with KT120s, part of what Iike about them in my setup. I prefer the midrange, and yet KT150s are totally neutral across the board in my amps biased at 45-50ma. Nothing really stands out with the KT150s I guess, maybe how it should be. Different rooms, hearing, and preference matters too, along with speakers, cables, now I'm digressing, in circles. Haha. |