Good 61NP replacement tube for NovaPre?

My Peachtree NovaPre (pre amp not integrated) will be returning this week from Signal Path from warranty repair. I though while I have it out of shelf, maybe a new tube would be fun to try. To be honest, I cannot tell much of a difference between tube and SS when switching (remote has tube off button). According to specs, the unit ships with a 61NP tube. So with that info, I am always looking looking to warm up and extend low end if possible (I know it may not make a huge difference). My current system NovaPre, B&K ST140 (last version), ZU Omen speakers (latest version), Oppo 103, Apple TV, and Canare 11 gage speaker wire.

Don't get me wrong, I love the way my system sounds. Just getting the urge to tinker. Also I wrote upscale audio...but no reply (afetr a couple of weeks).
Yes 6N1p. Hopefully I'm not stuck with a single manufacturer for a tube
One of my amps uses the 6n1p as driver for a 300b. I found the NOS ones to sound better. Do a search for one that has 6n1p-eb, Voshkod or has the "rocket logo" on it.
Don't waste your time...I tried rolling some NOS tubes in mine and the difference was too minimal to even describe. The tube is a buffer and EVERYONE I have talked to has said the tube sound is virtually identical to the SS sound.
You may wish to try using 2 tube dampening rings on each tube if you wish to change it's sonic character, i.e. too bright.