KT150 to KT120..or KT120 to KT150

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.

I concur @wolf_garcia , I recently ran an XA25 into a pair of refurbished Quad 57’s and resolution was off the scale yet retained a natural tonality and texture.

@decooney, I purchased a set of Silver 88 mono-blocks back in 2014. When I ordered them, I paid extra for the KT150 customizations. I had always been running KT150s, but recently tried some KT120s. I am finding less high frequency extension with the KT120, and less midrange lusciousness as well. I run the KT150 at 50ma, and the KT120 at 44ma.  Maybe I have not given the KT120 long enough, but they came out of a friend's CAT amps, so I think they have been run for at least a couple hundred hours. I am curious as to what bias you are running the KT120s in your Quicksilver amps.

Thanks

@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.