If I may, three different scenarios to share. The first two are friend’s amps I helped them with when they were ready to make tube changes. The last mono block amp(s) mentioned are mine.
1. The Jolida amp my friend Alan had KT150s in it, worked fine, sounded neutral, lacked the velvety rich sound. Swapped to PSVANE KT88s. More engaging now. My friend loves it, everything he was looking for from the sound in this circuit.
2. The Black Ice F22 my friend Richard has came new with lower grade EL34s. He swapped in new production Genelex Gold Lyon KT77s. He truly enjoys the change and sound after there was 50-70hrs on the 77s. He listens to it daily now. I don’t think he’ll ever try KT150s after hearing this setup.
3. My own tube mono block amps have massive transformers, came stock with KT150s, sound very linear, super clear, neutral, amazing sound stage and detail. The designer recommends running them as low as 40ma and high as 60ma. I run them at 50ma per tube. Sometimes I’ve felt it was lacking velvet tube sound, kinda missed KT88s. Can’t run 88s in my amps, too high of plate voltage. Split the difference with KT120s, a more lush tone. After the KT120s had 100hrs on them, I have no desire to put the KT150s back in immediately. KT120s were as close as I could get back to 88 sound. Been enjoying them past three months.
Your F22:
fwiw, I’ve heard your F22 amp and it can sound really nice moving from EL34s to KT77 or KT88s. Hey, KT150s are expensive. FYI, my four KT150s are sitting nicely tucked away in their boxes. Bigger is not always better, IMO. You can also try extra nice KT77s or KT88s s in the F22 if you want to stay closer to a rich full sound without being overly neutral. Trying to save you from skipping a good in-between option to consider. Some of my other friends rotate from 150s back to 88s, 77s - often.