Most of the sound in the ‘60s was in mono, many of the early stereo tracks had the limited tracks that were available from 4 or 8 track recordings shunted to either side, like drums one side, guitars the other, with maybe the bass and the vocals in the middle. Engineers had to focus more on the sound rather than where the sound was apparently coming from when recording/mixing in mono. These engineers and their trainees had decades of experience to call on so with the advent of stereo it meant a lot of the early releases were pretty crude - it took a while for people and the technology to catch up to the concept. Geoff Emerick certainly preferred the mono to the stereo mixes of the Beatles he did in those early days of stereo.
Half my record collection by the time I started working was in mono - but by the time I bought my first really decent turntable/preamp/amp and speakers, CD4, QS and SQ (and other not so popular or successful) quadraphonic records were starting to appear on the market, amplifiers from Pioneer, Aiwa, JVC, Sansui etc were available with some or all of the decoders for this, special cartridges with the ability to track to 50KHz were on the market as the CD-4 format used an FM-PM-SSBFM 30KHz carrier track that carried the rear channel information - the audio information reduced front channels were the difference between the “sum” full content LF/RF-LR/RR channels and the rear subcarried encoded audio LR/RR. This meant a quad record could be played on standard stereo gear with no loss of audio information.
There was an incredible amount of work done on the quad mixes compared to just mixing for stereo and in some cases the quad vinyl had a big edge over the stereo releases of the same material
The sonic quality and fidelity of emerging audio gear for vinyl was incredible for the time and some superb quad vinyl material was available. Simon and Garfunkel Bridge Over Troubled Water, Pink Flord Dark Side of the Moon, Black Sabbath Paranoid, Eric Clapton 461 Ocean Boulevard, Chicago, Miles Davis, Aerosmith, Mike Oldfield…….
Special studios were required to mix this stuff, and in most studios of all formats there was a load of earlier tube gear of all sorts mixed in with the new. All this by the early ‘70s. The same engineers who had been working in mono were now working in stereo and quad.
By the ‘60s audio technology was already in the solid state world so it would be hard to say what recorded material from that era was done on pure tube or hybrid or pure solid state gear. The same mics were being used as well as new arrivals. Rupert Neve built the first commercial solid state console in 1964 - by the end of the ‘60s there were many players in the same field with large track-count multitrack in mind - API, Allen & Heath, SSL and so on with existing manufacturers swapping to semiconductor based design. There is no blanket “60s” sound as it all depended on the studio and the available equipment, the engineers, the producers and of course the artist (not forgetting the budget from the record company) so there was a mix of the great with the awful and the in between.
