KT150 to KT120..or KT120 to KT150

@decooney Yes Qualiton X200 by Audio Hungary.

Each of these tubes has their own sound characteristics. 

KT 120 is a great all around tube for all types of music. 

KT170 and 150 I like for Jazz, Rock, Blues, really like the sound stage and upper end.

KT88 I really enjoy with  classical it is fuller sounding than the 120's

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.  

My Had amp wound up with GL KT66s, and I liked them so much I "panic bought" a back up pair. Great sounding tubes in a great amp...however...I recently bought a new Pass Labs XA25 and none of my tubes work in that amp (you can lay tubes on top of it or maybe cram some underneath)...that said, although not necessarily completely broken-in yet, I think the XA25 is an amp every tube freak (with compatible speakers and things) should hear. Good Ol' Nelson, whom I've admired for his DIY community support and First Watt stuff (never owned one of those, but still), has simply designed a killer thing in the 25...I've never heard a solid state amp that resolves detail and provides the astonishing tonal "rightness" like this thing...just pure Class A slam and life, utterly quiet performance with effortless clarity, accuracy, and soul for days...I'm smitten (smote?)...

@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.

I'm keeping my Had amp to use when I feel like it...it's a work of art and only uses 4 tubes so I want the amp to think I'm just giving it a well deserved break so as not to hurt its feelings. The Pass amp was bought out of curiosity after reading so many glowing reviews and opinions about it, and I generally like Nelson's open attitude toward the DIY community and his design ethic.