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.
I use gridded paper and pencil v1.0 which runs on most any human brain.. Sorry I couldn't resist, but I assume any good cad or drawing program - if you are looking for something with design rules I'm not aware of anything out there.