Why are older tubes so much sought after

I agree with Tvad.

So, the answer to your question is a simple one - because the old tubes sound better. And, the results are not even close.

I just built a Dynakit ST70 to play around with, and I was running the stock Sovtek 7199 driver tubes. Well, the amp was OK, semi-pleasant to listen to, and I threw the, "What do you want for $600?" tag on it. But, I couldn't get past how slow, plodding, and constricted it was. It simply would not get out of the way of the music. As for a letter grade, I gave it a C Minus.

I see several areas where the performance could be upped for free, but before doing that decided to buy an old set of RCA 7199 driver tubes to establish a baseline for what the amp should actually be.

Now, I'm often here preaching the benefits of maximizing one's output and driver tubes to wring as much performance out of their power amplifiers as they can get. I'm also not much of a fan of most Russian tubes at all. Wow, even I was not nearly prepared for the transformation! I've never heard such a performance increase from a tube change in my life. Right away, the sound opened up to where you would hope it would, that EL34 magic midrange arrived in spades, and bass is more extended and tight, and incredibly much more defined. It finally sounds like a tube amplifier. The amp now grades out to a solid B. Borderline B Plus. Perfect? No, not hardly. But I could sit down and be happy long term with it now just as it is. And, I didn't even start tinkering with it yet...

Rodman99999, I'm using the RCA 7199. Sylvanias were also an option, but most people told me the RCA were preferable. Not having tried the Sylvanias, I don't know how they stack up against the RCA, but I was assured either would be a tremendous improvement over the Sovteks.

I'll need to try an NOS rectifier, based on your recommendation.

As far as new production tubes go, there are several I like, the JJ KT88 and E34L and EH 6CA7 among them, along with the Shuguang 12AX7. But, apart from those, I come down on the side that the old tubes absolutely smoke current production.

Mrtennis, all I can say in response to your last post is, bullshit!

Juanpablocuervo and Chadeffect, it's so exciting that you two love the Sovtek new production tubes so much!

OK, so that everyone is happy and sees I am not an ungenerous person, I am willing to buy 1 Sovtek equivalent, be it 12AX7, 12AU7, or whatever for each old tube you can provide me. On top of that, I'll even pay for the shipping!

Man, you guys are going to make out like bandits.

My own personal feeling is that musical preference has little to do with what tubes (or, loudspeakers, amplifiers, CD players, etc.) I prefer. The best tubes, loudspeakers, amps, or whatever do best with all of the many genres of music I listen to.

I will say that personal preference does play a role. For example, many people feel Sylvania 6SN7 to be among the best of the bunch, as there is a clarity and openness there. But, for a lot of applications, I prefer the honkin' fat mid/upper bass that the RCA variants lend. Likewise, the Telefunken 12AX7 is consideres the gold standard, but I find Sylvania Triple Mica 5751 to be so much more open and beautiful, these tubes just seem to make everything bigger, and everything gets better with no tradeoffs whatsoever. Again, that holds true whether I'm listening to hard rock, classic jazz, or dusty 1950s female vocals.