• 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.

is it ok to open up a small PCB hole with a larger diameter drill?

Yes, though if the PCB is PTH type and you need contact on both sides, you will need to solder it on both sides. Be mindful of how much pad is left over after the drill. Less pad surface also means less adhesion and the possibility of lifting the pad/track.