Nonsense. Most modern power tubes are more than adequate for the job. Believe it or not some sound really good. And once you get a good 12AX7 (either new or old) it'll last for years, sometimes longer than the player. This really is about tone chasing tube rollers. And most tube rolling is based on a bunch of myths and unqualified hype. It took me a lot of time and money to figure that out. Sure, a Mullard EL84 would be optimal for your all original, 1962 AC30, but for an Orange Tiny Terror? It would make little difference to use old tubes when considering the ratio of price to any "improvement" in tone for most modern amps. My personal preference for old 12AX7/7025 tubes has to do with my bad luck with modern pre's and microphonics. Tone "improvement" is mostly marginal and varies too much to definitively say one brand is better than another brand with old pre tubes. I've had RCA 7025's and Mullard 12AU7's from the same respective batches sound different. Other old glass 9 pin pre's popular in guitar amps (12AU7, 12AT7, etc) are still readily available at good prices. Again, once I get a good 12AX7 (new or old) they stay in the amp unless they go microphonic. I have 50 year old 12AX7's still running in 50 year old amps I've owned for 20+ years. I miss the old RCA 6L6's, but no way I'm paying that kind of money when there are pretty kick *ss sounding new 6L6 variants like the Tung Sol 7591A.