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.
@elizabeth I hear what you are saying, and for some manufacturers this is fine, from Schiit (or is it iFi?) that have the sockets. But i think they might limit the quality the OP is after.

I’m not a purist, but I dont use the sockets that allow other tube types, b/c it is just another thing in the way of the audio chain. And the OP is looking for good tubes with good bang for buck. IOWs, I personally would not put a socket on a $75 NOS tube.

TBH, im not familiar with your CJ PV11, so i did a quick look up- this is from the 90s? and uses 3 different tube types? of course it is fine to have an older model, but that will tell us more about its general circuitry under the hood. Some amps can handle substitutions, some cant. Some pre amps now (LTA MicroZotl) have a choice of 6SN7 or 12AuX, b/c the circuit board and electronics inside support these different electrical platforms.

@rvpiano: i would like to make some recs on tubes, but it would help me/us to know:
1. Do you have a budget per tube or to replace all 6 right now? or replace just some? Whatever you do, swap out all the tubes of the SAME type. eg, dont replace one 12AU7, replace all of them at the same time. you probably guessed this, but some people dont.
2. I know the Nuforce class D amps you have, but what speakers do you have?
3. What particular aspects of sound quality do you want to change? more or less hi frequency? more or less mids? more ore less bass? more balance overall? a "sweeter" sound? a dryer sound? a colder sound? a bigger soundstage? a smaller stage? a more aggressive or laid back sound?  you get the picture....
Hi RV,

First, I note the following statement in the manual for the PV11:

It is well known that tubes of a given type vary sonically depending on the manufacturer. We have chosen the brands of tubes we supply based on extensive auditioning of available brands. The choice of brands has been made solely on the basis of sonic performance without regard for either cost or prestige. We know of no vacuum tubes available which will improve the sonic performance of your PV11....

... Please note: The indiscriminate substitution of type 12AX7 tubes for the 5751 will seriously degrade the sonic performance of the unit.

Also, apparently four of the six tubes in the PV11 are used in its phono stage, and only two in its line stage. And I would not necessarily assume that a given tube is likely to exhibit similar behavior in the two kinds of applications.

Given all of that, it may be worthwhile contacting CJ and asking if they can tell you what tubes were originally used in the PV11.

Beyond that, FWIW like some of the others I have had fine results with Gold Lion reissue 12AX7 and 12AU7 tubes, in my case in line-level and driver stage applications in a Chinese-made Paxthon integrated amplifier I used for a while some years ago. They handily outperformed a number of vintage tubes I also tried in that amp, including some vintage Telefunkens which go for considerably higher prices.

Good luck. Best regards,
-- Al

Never sub a 12 type tube for a 6 type tube. The number is the voltage. Hence 12ax7 is 12 volts! BTW, a 5751 has 30% less gain than a 12AX7!