All tube operating points below are by no means definitive good sound recipe for your particulate tube project. Lowest THD point is not necessary best sounding one and there is always some variance even in a NOS tube batch from the same manufacturer! Below information is only useful as a general starting point and is ment to get you in a ballpark when no measurement equipment is available.
What a superb triode! Just look at those curves. And no grid current with grounded cathode! So no more arguing about which BIAS led/resistor/capacitor sounds better 🙂 Noise floor is quite high, but considering μ of 70 it’s ok I guess. Available for sale.