Best cheap NOS tubes:GE, Phillips and Sylvania

Rocc - I'm very happy with Mullards in my premier 14 over stock GE and Sylvania. Try Upscale audio, at the very least you should have different types of tubes to experiment with. I was using stock for a while and switched speaker cables from Kimber 8TC to Alpha-Gore MI2's and the stock tubes sounded a little aggressive on the top end, especially on bright digital recordings. The Mullard's in this case are a better match, much less fatiguing, instruments sound more life like IMO....

The tubes need to be very low in microphony, and not likely to become microphonic OR noisy. That's not an easy task for the PV-10A, PV-11, and PV-12. Not easy for a CAT either.

They used RFT for a while at the factory. Those worked fine. Mullard sound better. I might suggest using the box plate version called a CV4003. They seem to hold up, if you get good ones to begin with.

Being up there, you are best off finding the cheapest 6GK5 you can get and weeding through them yourself, esp if on a budget.