If you have not already done so, please read the first part of this book, "How Tube Guitar Amplifiers Work (Part 1) - Explanation of the Circuit Diagram" first.
After reading these two books, you are now ready to modify your own amp with your own hands.
Please create your own best distortion sound.
In Japan, it is not common to modify tube amps by yourself, but you can experience a big change in sound just by changing the cathode resistor of the pre-tube or the constant value of the bypass capacitor.
I sincerely hope that you will read this book and, through trial and error with your own hands and ears, pursue the ideal sound that is ringing in your head, and then obtain it.
ce-Crash Sound Source
Low-Gain Version

https://youtu.be/zjXYbWwj_U8

Mid-Gain Version

https://youtu.be/WI_vYP_lUZc

High-Gain Version

https://youtu.be/4hCxyhJdVq8