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.
Bond it to the chassis (which should be bonded to mains earth). This will improve safety and may reduce RFI. Signal earth is a different thing and should be bonded to chassis at the input of the most sensitive stage in the system (usually the phono stage).