The C-J PV14L preamp is not exactly the best candidate for tube rolling, but I do have some experience with the dfiference that tubes can make. The PV14L only uses one pair of tubes, as the preamp only has one gain stage.
The second version of this preamp (which mine is) was built around the Mullard M8080/CV4058 tube. When I received the preamp, it sounded good with the tubes provided, but I found that they were highly microphonic, exhibiting a rattling noise on certain loud notes. I had ordered in a pair of Tung-Sol 6C4s to try. They sounded slightly better, yet there was still some evidence of microphonics. Just not as pronounced as the Philips ECG 6C4s I had replaced but still unacceptable.
When the Mullard M8080s came in (from a UK seller), right away I noticed that there were no microphonics whatsoever. Sonically I did not notice a huge difference between these tubes. If anything, the sound was slightly more mellow and balanced with the M8080 than with the others before it, the Philips ECG tubes perhaps being the brightest and maybe slightly more etched of the pair I tried. However, these latter tubes had an unknown lifespan on them–I believe the seller mentioned they were about “halfway used.”
In the meantime, I had gotten in some silicone o-rings to try as tube dampers. A bag of 10 properly sized o-rings is only a dollar or two; some audiophile tweak companies charge ten times this amount for the same thing! There is no difference. In fact, the silicone o-rings that ship with the PV14L are the same material, just of a smaller thickness. The inner diameter of these tubes is tighter, so it takes a little more effort to place on the tube. But, that should assist in better dampening.
As one of the M8080s has gotten noisy (the seller is thankfully sending a replacement at no charge), I placed the 6C4 Tung-Sols back into the preamp. The thicker tube dampeners have made only minimal difference in the microphonics of these tubes. Dampeners can help with by reducing some of the vibrations but, of course, will have no effect on any of the tube components physically rattling inside the glass.
Seeing there aren’t many options in this family of tubes, I will stick with the M8080s. The CV4058 is actually a military spec tube, made to more durable specs and tight tolerances, hence the absence of the microphonics. There are still plenty out there, and it is not a popular audio tube. An older McIntosh component used the 6C4, and C-J has used this in three of their preamps. These tubes do so much right that I don’t really see a point in changing out the tubes for a different sound.