Question for tube aficionados

I have always gotten solid advice and feedback from Brent Jesse, Andy at Vintage Tube Services, and Upscale Audio. I’ve purchased from all three over the past 20 years, and have not gotten a bad tube from any of the three. 

I would start by replacing the two 12AU7s in the line stage with a very high quality matched pair, as all sources will run through that preamp stage. Replace each additional tube type in phono section in stages to evaluate what each is doing to your sound for your future reference. You may notice some tube positions make larger differences than others.  Have fun!

The Joe's Tube Lore posting is from 1999 from the looks of it, but I didn't read down through the pages. You'd be hard pressed to find much for $5 these days!

The 12**7 tubes last quite a long time, so it's well worth it to step up to something really nice. The Brent Jesse descriptions of the sound qualities of various tubes is very helpful and accurate. As long as the 5751 and the 12AX7's in your PV11 are quiet, I'd go for the gusto on the 12AU7's for line stage... unless, of course, your budget allows for doing them all right now.

I have some experience with the 12AX7 from Psvane. I would definitely give them the nod over all current production tubes that I've tried, except the Gold Lion. The GL gets the nod for tighter, more tuneful bass.

I would not put either brand ahead of a quality, tested, NOS Mullard, Amperex Bugle Boy, Siemens, or Telefunken in sound quality. As with all things audio related, this is a subjective statement. There are other NOS than can be quite good, of course, but those are the biggies. They all have a sometimes subtle, but definite and unique sound character. The different brands will excel in different equipment and systems, and based on listener preference, of course.

I'm not surprised that you are digging the Amperex tubes, as that is one heck of a 12AX7... plenty of detail and the tube black magic, and a nice match with a neutral-to-cool sounding amp. If still running the Belles, I would expect many to lean toward the Siemens or Telefunken. All just generalizations and personal preferences on my part, of course. 

If you can afford to keep both, do it. You may decide to make a power amp change down the road, and those NOS Telefunken tubes could come in handy... they're not going to go down in cost in the future. I could kick myself when I think of the NOS tubes I've sold along with gear over the years.