What I was trying to say is that what you describe might happen after many years (and that's actually the case if one uses a good pot) or the amp is not really used and actually spending most of its time collecting dust maybe in a dump place. I have done it to know that is not a problem and I never make choice giving un-necessary importance to minimal risks otherwise I should just travel by plane and never use a car, for example. I was not saying what one should do or not do. If one is using vintage stuff then adding resistors is certainly a must. It was just a comment based on my experience, not suggestion. My suggestion is no AC supply at all. Having read half a page I think that visiting that site would be a waste of time for me.
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Worth noting that the Intermodulation spurs (frequency terms at 50/60, 100/120... and upward) have an amplitude that does not usually increase linearly with the test tone's amplitude.
This happens because with AC-heating, you have to adjust the hum-pot to get minimal hum, when the amplifier is at idle.
The pot adjustment locates the best symmetry in the triode curves, with the AC-heat waveform applied both to Vgk and Vak and skewed along the filament by the varying filament voltage along the filament's length. It is more complex that it might appear at first glance.
But this symmetry only applies for zero music signal amplitude. The symmetry breaks down with increasing music signal, because the triode curves are shifted into a different region by the music signal, and it makes the IMD bounce up and down somewhat unpredictably. This does not produce a natural sound, for sure.