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? 
749cdfb3 0814 490e b189 a364ad773263daveyf
First of all, please ensure your amp manufacturer is on board. With that disclaimer, I went from a kt120 specified ARC vsi75 to a kt150 specified ARC gsi75 some years ago. I presently utilize an ARC ref75se and love it. The amp specs between the two integrateds are virtually identical but the kt150 is a far superior tube to my ears. It is smoother and yet more dynamic. More texture while having a less grainy presentation. Of course it all depends on the amp and the plate voltage. Your amp may be able to utilize the kt150 but it may not be able to take advantage of its strengths if it simply puts out the same plate voltage into both tubes. 
Kt150s cost roughly double so if your amp doesnt exploit its strengths by running them at the appropriate specifications its likely to be an underwhelming result.
I have a Carver Crimson 275 that comes with Tungsol kt120's.  Tried  kt150's and preferred the 120's.  Seemed like the 150's were just too much oommph, if that makes any sense.  After that I just recently got a quad of the new Shuguang Dawning series wekt88 Plus tubes.  They are great!  They are the result of top Chinese engineers attempting to manufacture the finest current tube using the best materials and tooling available.  In the past I wouldn't give you anything for a chinese tube, but then I got a preamp with these same series we6sn7 plus tubes and they were also fantastic.
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.

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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.

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If unsure, defer to the amp designer about "what output tubes" to run.



Hi Dave

I have had a KT150 amp on loan to compare with my KT120 amp. 
I prefer the KT120. There is just something about the KT150 I find too Hi-Fi sounding and cerebral.
I wouldn’t characterise the Kt120 as dry at all. I think it’s a blend of a EL34 and a good 6L6. 
It just sounds a bit warmer tonally to me than the KY150 which does all the Hi-Fi tricks very well. 
I’m sure it comes down more to implementation than the actual tube. 
I have to add that the KT120 takes hundreds of hours to settle in and I think that’s why people dismiss them to soon. 
All the best. 
I ask the question in my OP because there is a well known and respected (justifiably so, IMO) amp designer, who believes that the KT120 is superior sounding to the KT150. This has NOT been my experience, but i am questioning if others have experienced the same results as the designer claims.
Would love to know the amp designer. I have been saying the same thing but everyone seems to be on the KT150 bandwagon. 
Keep us posted if you give it a try. I think you are safe to swap them in your Jadis. Might just need rebiasing?



@dsholl1
There is just something about the KT150 I find too Hi-Fi sounding and cerebral.I wouldn’t characterise the Kt120 as dry at all. I think it’s a blend of a EL34 and a good 6L6. It just sounds a bit warmer tonally to me than the KY150 which does all the Hi-Fi tricks very well.
I’m sure it comes down more to implementation than the actual tube.

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.
Interesting, 
I have the Bob Carver Raven 350 mono blocks that use KT-120 tubes and I have been wonderin' if the KT 150 tubes would be better.
Bob Carver told me they would work fine with the amps but he was reluctant to say if they would be an improvement.

ozzy 
@dsholl1 I don’t want to tell who the amp designer is, but I really like his gear and I respect his opinion ( generally). However, my opinion is that he is mistaken when it comes to the differences. @decooney What you posted about the quality of the driver tube is exactly my experience as well. Right now,I am using stock EH driver tubes in my amp, but I have rolled in a variety of NOS vintage tubes...and the difference is not slight. The KT150’s really seem to light up bass on what is upstream. Since the amp designer I am talking about doesn’t believe in NOS vintage, I would strongly suspect that this is where he is basing his finding on..a mismatch between th driver tube and the KT150, leading to his favoring the KT120.( in his particular amp). Nonetheless, @dsholl1 in what context( amp..driver tube etc) did you find the KT120’s better?
@daveyf  I listened to the Jadis DA88smkii compared to the i50. I much preferred the 88. The 88 was considerably more expensive too. It just has such a musical sound with massive amounts of density. The i50 sounded very clean and Hi-Fi. The i50 has better bass but lacked density and warmth if that makes sense?

 I would’ve bought the 88 if it wasn’t so damn expensive where I come from. 
@dsholl1  Unfortunately, I don't believe that you can lay the differences that you heard between these two designs, the i50 and DA88sMk2, at the feet of the power tubes utilized by these amps. There are signifiant differences in amp abilities as you go up the Jadis line, just like most other manufacturers. There is a reason for the price differentials. 
@daveyf

decooney What you posted about the quality of the driver tube is exactly my experience as well. Right now,I am using stock EH driver tubes in my amp, but I have rolled in a variety of NOS vintage tubes...and the difference is not slight. The KT150’s really seem to light up bass on what is upstream. Since the amp designer I am talking about doesn’t believe in NOS vintage, I would strongly suspect that this is where he is basing his finding on..

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.