Try it with the stock tube. You probably won’t hate it, but if you do I’m not sure another tube will fix it. I’ve seen several 6SN7 shootouts, one was even using several Sagas and blind. A NOS tube can sound better, but ask yourself how much you are willing to spend on a tube compared to the price of the preamp before getting sucked down that rabbit hole. There are tubes that sell for more than you paid for the Saga.
I put a Raytheon VT-231 in my Saga+. Mostly it was out of curiosity as I’m pretty new to tubes. Might try some others eventually to see if I can get a better feel for tube characteristics so I’m capable of describing differences with more detail than I like it. Even if it’s obviously better, it’s hard to describe in terms that aren’t a basic salad of audiophile buzzwords.
