Each stage of preamplifiers was designed with the help of this "test equipment".
Right part is the tube version of the stage with input and output interstage circuits.
At the FET part, I first set up the gain below the cathode circuit cutoff frequency of the tube stage by adjusting the resistor at the FET source (adjusting biasing voltage at the same time to keep operating point).
After this I added a correcting RC circuit at the FET source to adjust gain above the cathode circuit cutoff frequency of the tube stage. R define gain, RC define cutoff frequency.
Frequency response i checked by "RightMark Audio Analyzer".
Thats why you don`t see original values of components in source networks.
The last thing I adjusted the parameters of the "scalable diode" part to provide adequate "grid" limitation.