KT150 to KT120..or KT120 to KT150

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?

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.

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. 

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.

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.

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.