Question for tube aficionados

I contacted Conrad-Johnson.  They sell a complete set of recommended tubes for the PV 11 for $310.
I wonder if I should go in this direction.

The Conrad-Johnson description of the tubes is as follows:
 “V1 & V2: 12AX7 MULLARD| V3: 5751ELECTRO HARMONIX | V4, V5 & V6: 12AU7 YUGOSLAVIA.”

No further description than that.

It sounds like these are new production tubes. To go in this direction would get u right back where you started.
The only upgrade path is to try NOS. 

I think lowrider57 may be incorrect. The Mullards could be new production or old. The Yugoslavia 12AU 7's are definitely old stock. They haven't been inproduction for 20+ years. When this unit was first produced I don't think  new production Mullards were available - my guess is that they are more probably old stock and I think that the NOS and new production do not have the same tonal qualities. 

I'm not familar with your pre-amp but I suspect that the V1 and V2 positions are likely the positions most affected by tube changes. If that is so, and if I wanted to play with tubes changes, I would start there keeping in mind that different brands have different tonal qualities and it helps a lot in selecting tubes you want to try to have some 'tonal' goal and try tubes that have a similar tonal signature.

@newbee , you may be right. I traced the PV11 preamp back to at least 1992, so the Ei and Mullard could have been NOS. But CJ is now re-tubing the unit, and $310 is a very low price to include 2 NOS Mullards.