KT150 to KT120..or KT120 to KT150

@vinylvalet  Do report back once you receive and have run in your new Zesto amp. I am particularly curious as to the difference between the KT150's and the new KT170's.

I would expect the amp to be basically idling when driving your Fyne's...with all the tube choices.

I went from kt120 to kt150. I just liked the sonics a lot more. Everyone has different ears and amps

My Qualiton X200 came with KT120's and sound very nice.

Decided to go KT170 and guess what the 120's are sitting in a box. I also have KT150's but prefer the 170.

KT88's I bought cheap are never going back in.

I've tried GL KT88 (stock tubes), KT120, and KT150 in my VAC Signature 200iQ monos. The KT150 were the most recent acquisition - and they were terrible. Extremely powerful low frequencies and gobs of slam - which honestly was fun - but it completely swamped the rest of the spectrum and was a very unbalanced sound. 

The KT120 - I like them a lot. They're not as polished and refined as the GL KT88 in this amp, and so I think most will prefer the 88's here, but I also think the KT120 are at least competitive here (unlike KT150). I'd gotten so used to the KT120 sound over 10 years of use in Rogue Apollos, that I think it's been hard to wean myself off them in the VACs. They feel like home base lol. I'm currently, maybe, transitioning from KT120 to GL KT88 in my VACs.

I'm sure the KT150 performance is very amp dependent, and I believe they'd be fantastic in an amp properly designed for them - but not in the VACs.

[Initial burn-in matters on these tubes].  I underestimated this on the first try.  

KT150s:

AFTER 200hrs of play, I now consider the KT150 as a sort of a  "do no harm" output tube in my mono block amplifiers. Brand new, I did not like them very much.  Way better after 200-300hrs.  I had been comparing back and forth with my audio local dealer too in the same amps. Top end smoothed more at 300hrs, wearing in.   

KT120s:

In similar fashion, I did not like them brand new in the first 24-48hrs.  In fact, I passed over them too quickly jumping to KT150s prematurely. Missing velvety texture, tone, gave them another shot and super glad I did. At 72hrs+ started showing some hope with a tad rolled off highs/lows. Nice though. Easy listening.