The main question I want to ask, does maximum plate power dissipation stay constant over all voltage ranges or does it increase as plate voltage increases? Existing bias charts ( weber vst, Jim jones), and bias calculators use one value for max plate dissipation for all plate voltages. The tube spec sheets show the max plate dissipation rising with the plate voltage. I did bias charts both ways, here is the sliding scale I came up with: The 6v6 is a seven watt tube at 300 volts (matches the spec sheet) rising to a 14 watt tube at 450 volts (matching reality) The 6L6 is a 22.5 w tube at 400 volts rising to a 32.5 watt at 500 volts. Here is my argument for a sliding scale. The tube can handle more power at higher voltages. At lower voltages, the current would be unpracticable to reach the full power like a 6v6 putting out 14 watts at 300v. Here's where my argument breaks down. For a 6v6 to be a 14 watt tube at a low plate voltage like 300 volts, it needs 46.7 mA of current, and 28 mA at 60 % idle. It doesn't sound unlikely, it doesn't sound like too much current to work. Here's my samples for the 6L6, unfortunately I don't know how to show data on this forum, so it's just photos. The first is the 6l6 with constant power out no matter the voltage, the second is the sliding scale.