How can it be that some old recordings sound sublime?

Class A tube mastering amps, tube microphones, minimal miking and a real sound engineer with real ears doing the work. Simple
enough as opposed to most of the dreck of today

All the above I agree with. But I am struck by the assumption implicate in the question, that newer recordings should sound better than older ones. In many fields, newer is almost always NOT as good as older. In Vintage Drums for instance, the most desirable and expensive snare drums are Ludwigs from the 1920’s. Not just because of their rarity and collectability, but because they sound better than newer ones. They were made in a way (I won’t go into the details here) that was expensive (they were over $100 in the late ’20’s, a LOT of money at the time), and the Great Depression brought an end to their production. No one has ever resumed making them the way they were in the ’20’s, certainly not Ludwig.

Microphones and other recording gear from the 1950’s and ’60’s is very desirable amongst recording engineers, and fetch high prices when sold. They often possess a sound quality rarely matched by newer gear, just as some (Many? Most?!) old recordings sound better than newer ones. Age or era alone is not the determiner of quality. I don’t understand the assumption that it is, could, or should be. A 1950’s and ’60’s Corvette was a far better car than the Corvette of the late 1970’s and ’80’s, when emission regulations forced a change in engine and exhaust design.

Contemporary recording equipment and technique is not necessarily about achieving sound QUALITY ya know. Not to mention the fact that recording engineers these days are too commonly somewhat ignorant practitioners in their field. I was at a session where a "school" educated young engineer placed an ambience mic right in the upper corner of the studio and recorded the sound emanating from it. The very spot we audiophiles put absorption because of the nasty sound that room corners produce! His "education" obviously did not include even basic acoustic theory or he would have known what that would sound like when recorded. Recording engineers of the ’50’s and ’60’s had learned their craft the old way---not in a "school", sitting in a class, but working as an apprentice, a "second" engineer, side-by-side with a master. They were in many cases radio engineers in World War II, and when they returned to civilian life went to work in early recording studios, before there was even such a thing as a tape recorder. By the time they were making those legendary great sounding 1950’s and ’60’s recordings, they were masters themselves. There is a fantastic documentary entitled "Tom Dowd and the Language of Music", in which Tom, engineer of many great recordings (as you will learn in the doc), tells us all about it. A MUST see, it’s available on DVD.

In the 70’s I made some recordings of my Jump Blues/Swing band playing live, using a pair of omni condenser mics straight into a Revox A-77. No pre-amp, no mixer, no EQ, no compression, no limiting, no noise reduction---no nuthin’. Those recordings sound more like life music than 99.99% of my LP’s and CD’s. I use them to evaluate Hi-Fi equipment, especially loudspeakers. I also recorded solo speaking and singing voices, and those recordings are invaluable for ascertaining the freedom from vowel colorations of speakers. Electrostatics = excellent; magnetic-planars = very good to excellent; dynamics (cones and domes) = okay to very good; horns = not so good. Just kidding!

The sound on 50’s and 60’s LP’s are recording engineers of the time attempting to make "High Fidelity" recordings, capturing the sound of live music. The closer the sound of the recording to live sound, the higher the fidelity, of course. In the documentary I mention above, Tom Dowd is shown in the studio, walking around the musicians, stopping in front of each and listening. He then returns to the control booth, making adjustments to his recording equipment to make the sound in his monitors more closely resemble that of the live sound he just heard in the studio.

When I’m in the studio now, the engineer usually compares his recorded sound, not to the live sound in the adjoining room, but to commercial recordings, a/b’ing between his recording and a hit CD. It’s relative fidelity, not High Fidelity. The intent of engineers now is quite different than that of the guys who made the recordings "we" think sound so good. "Fidelity" is now a quaint notion, of relevance only to audiophiles. Hardly the target audience of the vast majority of record companies!

But the best recording engineers of today (Kavi Alexander of Water Lily, Keith Johnson of Reference Recordings, Pierre Sprey of Mapleshade, Barry Diament of Soundkeeper Recordings) are as good as any of the old-timers, maybe better!