Can excellent tubes transcend modest amps?

Actually- The better and more resolving the equipment and system, the more you will be able to appreciate the difference NOS tubes make. I'm referring to some of the Holy Grails here(ie: Telefunken ECC801S, Siemens CCa, TungSol JAN CTL round plate, Sylvania JAN CHS/6SN7W tall bottle, etc.) and not just any NOS tube. The benefits of finding and installing a strong pair of NOS drivers/phase splitters in your amps will far outweigh the costs/time involved. The differences between these NOS and ANY new production tubes are NOT subtle either. Don't allow your ears to be ripped off by heeding the nay-sayers who, for the most part, have never listened to a system equipped with the best of the NOS valves. As far as output tubes: The prices of matched sets of NOS anything are now obscene(I WAS using matched octets of Phillips ECG 6550s in my monoblocks). I'll now only purchase outputs from Upscale Audio, as their screening/matching/burn-in procedures are second to none, and Kevin has always directed me to the right power tubes to suit my equipment and tastes in music reproduction. Happy listening!!

No.

You can put great tires on an Impala and it's still an Impala.

Not the expert, but you can put moderately priced NOS tubes in moderately priced well built amps and take the musical enjoyment up a seveal notches

IMO, NOS is very overrated. The most important thing is quality capacitors, well built power supply, quality circuit, and a well matched dammping factor between amp and speakers. NOS is just a blip in a far more complex chain of events. Good tubes by Winged C, and JJ are as good as NOS, and even better in some cases. NOS is a good way to make a lot of money on old tubes. NOS is hard to match, and many have a lot of hours on them. I like new, but do have NOS too, I just buy new now after comparing the two. A bad circuit cannot be saved by NOS. Point to point with no PCB is great and quality caps like v-cap will do more than NOS ever hoped to do. NOS and power cords are similar IMO in that they are very over emphasized and emphasis should be elsewhere. Jallen