A very interesting post by Yaroslav Voronov on the Facebook Tube amp builders (DIY) page:
? Perfect GIF to get people to understand the concept of Ultra-Linear. Here, we can see a Russian 6P14P (EL84 equiv.) traced with the tube going from Tetrode to Triode connection gradually, the percentage of tap is on the top right. The knee point drops rapidly until it's non-existent, but the linearity increases at the same rate as you can see, in other words gaps between control grid 2V steps get more even as the percentage of tap goes up. So a gradual sacrifice of power for linearity.?
Here is the original link from hi-fi.ru
? Perfect GIF to get people to understand the concept of Ultra-Linear. Here, we can see a Russian 6P14P (EL84 equiv.) traced with the tube going from Tetrode to Triode connection gradually, the percentage of tap is on the top right. The knee point drops rapidly until it's non-existent, but the linearity increases at the same rate as you can see, in other words gaps between control grid 2V steps get more even as the percentage of tap goes up. So a gradual sacrifice of power for linearity.?

Here is the original link from hi-fi.ru