A final comment - one reason older tube amps are so desirable is that the output transformers in tube amps take forever - years - to fully break in. This is one large advantage five to ten year old amps have over new ones.
Although beside the point, another thing to remember is that the tubes are the circuit in a tube amp - if you retube the amp, you essentially have a new amp, this providing a gigantic advantage over solid-state amps for longevity (some high-profile solid-state amps become door stops if they ever lose an output transistor because the transistors have gone out of production - this won't happen to a tube amp that uses output tubes common in the tens of thousands of tubed guitar amps that are sold each year, e.g., EL-34's, 6L6, 6V6, 6550, etc., or that use a classic triode like the 300B).
A really good tube amp is like a Porsche 911 - a bit tricky to operate and conceptually not the most up-to-date, but capable of extreme performance and it will be around when most everything else is long gone.
Although beside the point, another thing to remember is that the tubes are the circuit in a tube amp - if you retube the amp, you essentially have a new amp, this providing a gigantic advantage over solid-state amps for longevity (some high-profile solid-state amps become door stops if they ever lose an output transistor because the transistors have gone out of production - this won't happen to a tube amp that uses output tubes common in the tens of thousands of tubed guitar amps that are sold each year, e.g., EL-34's, 6L6, 6V6, 6550, etc., or that use a classic triode like the 300B).
A really good tube amp is like a Porsche 911 - a bit tricky to operate and conceptually not the most up-to-date, but capable of extreme performance and it will be around when most everything else is long gone.