Sidssp makes a valid and important point, and I would argue further that the "sound" of a tube is confined what the specific tube IN A SPECIFIC CIRCUIT (Topology, Transformer, Driver stage, coupling etc.) can/will deliver. The second point - to reiterate - is the 811 (and 805, 845, 300b, 2A3) is (are) triodes - that is they have three elements, Anode(Plate), Cathode(For many triodes, the cathode and filament are the same, or called: 'Direct Heated') and screen or grid. the 6L6 is a 'Beam Power Amplifier'-per the RCA manual - and is actually a tetrode, or four element tube with 2 screen/grids and an extension from the cathode to focus the beam. They are not the same beasts....