Question for tube aficionados


I have a vintage Conrad-Johnson PV 11 preamp.
 I’ve always re-tubed it  with the cheapest tubes from Tube Depot (e.g. Electro-Harmonix 12AU7 and 12AX7, Sovtek 5751 and the like.). I’ve been very happy with the sound.
 My question is:
 Would it be worthwhile to spend more money on more exotic tubes?
  Would there be any appreciable difference in the sound?
 I’m powering the system with NuForce Reference 9 V3 monoblocks.
128x128rvpiano
I have a near 25 year old Audio Research pre-amp that came new tubed with Chinese 6DJ8.  I liked the sound quite a bit and decided after a few years to experiment with tubes. Holland, Bugle Boys, Amperex and so on came and went.  ..many different manufacture countries and brands  rolled in and rolled out, until I encountered a Siemens & Halske 6922 grey plate from the late 50's - early 60's.  That was the tube of choice for more than decade until I tried a 1959 Valvo Pinched Waist 6922 Cca, which was great for about 2 years of light use when it began to fade musically. Now it's a 1975 silver single wire Reflector 6N23 which is king of the hill.

The point being the right tube(s) can make or break your sound.  Do some tube rolling. What doesn't work for you can probably sell easily on eBay.
I used to have both the PV11 and PV12. NOS tubes did sound better, but if memory serves, seem to recall in both preamps the tubes were run in a current starved condition. You may want to measure the current/voltage flow through the tube. I dropped the plate load resistors and got much more open sound, but do not remember the values.

Still wish I had my PV5...that preamp made real music.

best.
doing the CJ tube replacement for $310 would be a quick and easy way to get things squared away. Then, down the road, you could roll some tubes. But I'm sure part of that $310 is a fee for their special knowledge of the right tube combination. Maybe not the best value per se, but definitely a quick and easy way to clean the slate and start from a proper baseline. 

But i would have to agree that the Gold Lyons would be more of a lateral move. Absolutely nothing wrong with that, but i just try to make a little bigger move when I do an upgrade.

I'm not talking about exceeding the $130 budget either. But the sound quality gains will be significant, especially since preamps tend to have more influence on the final sound characteristics than amps (and yes, I know, I know, some of you will argue with that ... yeesh).

In fact, you may just ask yourself, "why did it take me so long to figure this out ... :)" 
As a general note, please remember also that replacing a tube alone is not good enough. Compensating tube production variations, tube aging (and, especially, when using equivalent models) always demands a check and adjustment of bias voltage. I experienced surprisingly significant sound differences from the bias voltage differences of 5%. To make it more challenging, certain systems will benefit from setting a bias voltage that is different than the one recommended by the amp manufacturer. Additionally, my recent observation indicates that the replacing tubes and adjusting bias can also introduce embellishment and extension of trebles that can be easily taken for increased resolution while it only adds graininess.