• 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.

Static noise

Welcome to the Tubes / Valves threads.
Thanks for telling us in Post # 1 that this is for a guitar amplifier . . . I appreciate it.

Did you try a different shielded cable?
Did you try a second guitar?

Someone on the Instruments and Valves threads has probably already experienced your problem, and fixed it.