There is no "triodfied" pentode here but as you say results are similar to pentodes with cfb. Triode strapped pentodes only manage good efficiency at typical 5% THD if have good gm but rarely go beyond 25%, IME. Pentode with cfb is a different story and that is the configuration that is comparable here. The 811a is just a high mu triode and the 46 is a dual grid device with 2 modes of operation as triode only. The standard 46 triode is just as linear as 300B, the other one (originally intended for class B operation) is pretty linear too. For sure more linear than pentodes. That's why I am confident 5% THD is a rather easy target for 4W output class A2 (or 8W for the PSE). It will be less with 5-6 dB cathode feedback. Max power for SE triodes has always been rated at 5% THD where the distortion as function of power typically changes slope and rockets (clipping). Up to that point feedback will be pretty much effective. You can see that the zero fbk 46 Class B amp has more (crossover) distortion at low level than at max Pout.....
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