The Amperex white label PQs should be a great way to learn what is possible beyond the stock tubes. I've run a variety of Amperex, Telefunkens, Siemens 6DJ8s and 7308s in the ARC PH7 with results easily better than stock.
The trick will to use tubes that are quiet. Before purchasing pricey NOS tubes, get some assurance from the seller that they've been tested for noise. In a vinyl system the majority of all signal amplification happens in the phono stage and you'll learn pretty quickly if its tubes are microphonic or otherwise noisy. To an extent all tubes are noisy. This can be diminished (more or less based on the tube's condition) by using some sort of dampening. I don't know if the PH3 came with tube damping O-rings but ARC includes them with the PH7. And better than those are the ones from Herbies Audio Labs (no affiliation, happy customer). Best of luck with your tube rolling!
Tim
The trick will to use tubes that are quiet. Before purchasing pricey NOS tubes, get some assurance from the seller that they've been tested for noise. In a vinyl system the majority of all signal amplification happens in the phono stage and you'll learn pretty quickly if its tubes are microphonic or otherwise noisy. To an extent all tubes are noisy. This can be diminished (more or less based on the tube's condition) by using some sort of dampening. I don't know if the PH3 came with tube damping O-rings but ARC includes them with the PH7. And better than those are the ones from Herbies Audio Labs (no affiliation, happy customer). Best of luck with your tube rolling!
Tim