I have the Pathos Classic One MKIII and have tried many types. My suggestion is to get a Platinum grade, matched pair of Matsushita 7dj8’s. These are excellent, affordable and will work great in your amp.
https://upscaleaudio.com/collections/preamp-tubes/products/matsushita-national-pcc88-7dj8
https://upscaleaudio.com/collections/preamp-tubes/products/matsushita-national-pcc88-7dj8