Welcome. 6JD8, 6922, 7308, 7DJ8 to name a few majors.
I’ve enjoyed the BHK pre for more than 3 years. It’s a fine unit.
You’ll find volumes of information here: BHK Preamp tube rolling
My favorites tubes in the pre are in the 12v family. 6v and 7v tend to be noisy or not last long in my unit. Each unit will have a tolerance so don’t be afraid to try. Just know that is was intended to run 12AU7 or compatible tubes with the secondary ability to run 6/7v. Others have had a great experience with 6/7v tubes but they tend to be some rare, expensive versions.
Don’t discount the stock tubes. I would give them 100 hours playtime. They need a few hours to settle and more importantly so does the preamp.