Based upon this information, I cycled the EF86 heaters between 3.15V and 6.3 volts, on a 5 minute at normal and 5 minute at low heater voltage cycle. Triode mode, flat. This produces a bias voltage of about 2 volts, with about 110 to 120V on the plate. Noise is the input referred equivalent RMS noise. See my noise tester schematic for details.
Operating point remains the same.
Pentode mode, flat. The only difference is the screen fed with 120V directly. Similar to triode mode RIAA, except screen fed with 120V directly. They are now substantially better than the Amperex. They exhibit some low level of microphony.