WARNING: Tube/Valve amplifiers use potentially LETHAL HIGH VOLTAGES.
Building, troubleshooting and testing of these amplifiers should only be
performed by someone who is thoroughly familiar with
the safety precautions around high voltages.
With a high gain triode, mu=100, then it would look like 1.2nF to ground from the input circuits point of view, reducing gain above 130kHz or so (with that 1k resistor)