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.
Given there is no feedback, and a 1N4007 has pretty low junction capacitance (20pF at 1V inverse), and from what I think will be a high frequency roll off that would be dominated by the miller capacitance compared to Cgk, I wouldn't be concerned.
