Some years ago I regularly use #26 preamp (filament biased, CCS loaded, parafeed output to S&B TVC) and very satisfied with it....but IMHO TT (thoriated tungsten) filament is the another world. I'm in love it.
I tried #01 (UX201). It has wonderful tone, but (for me) driving capacity (I use TVC) is problematic (see Ale's site
Slew Rate (Part 2) | Bartola Valves ).
I continuously use 841, 10/10Y/VT-25, 801/801a/VT-62 tubes in my VAS, CF and output stages with excellent results.
The topology is usually simple, but no free lunch. Separated (filament transformer, raw DC PSU and -I use Rod Coleman' type- regulator) filaments, optionally filament bias, significant - 20-30mA -anode currents, silent HT PSU(s), large heatsinks etc.
My humble rule: every 1 kg amplifier needs 10kg PSU.
I'm on the finishing state of 801 (or 10 and variants) preamplifier.
Filament biased (Rod Coleman V7 regulator), gyrator loaded (Ale's design), capacitor (V-Cap CuTF) coupled. The volume control is one TKD potmeter in the input.
The PSUs is in the other box: two raw filament supplies, one common HT (300-320V, cLCLC).
I will try it with graphite anode 801 tubes.