KT150 to KT120..or KT120 to KT150

@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.

@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.

@decooney  I do agree that the design of the circuit is a major factor in whether the KT150 or KT120 is going to be preferred. The amp designer in question is absolutely convinced that the KT120 is superior to the KT150 in SQ. i think while this might(?) apply to his particular amp circuit, it certainly is not a universal. ( even though this guy would like everyone to believe that it is!)