my Cayin came with Cayin branded 6sn7 and 6sl7.
one burnt out, I tried a pricey pair of .... from Brent Jessee. Definitely changed the sound, I did not like them. Brent had me burn them in 60 hrs, then decide.
He let me exchange them for a different brand, half price, they sound terrific. I paid shipping, he refunded the difference in price.
IOW, research, ask, buy from someone like Brent Jessee who will let you exchange them till you get the magic.