Peter Bartok, as it turns out, was the son of the famous composer, and after coming to America, became the engineer for Folkways Records. The AudioXpress article not only has a wide-ranging discussion of the early days of magnetic tape and the LP record, but also has two circuits from Peter: a mag-tape preamp dating from the late Fifties, and the all-tube cutterhead amplifier that he used for mastering records.
There’s also a sidebar on the equalization choices made in the early days before RIAA equalization became the standard - a straight 6dB/octave slope over the whole audio spectrum gives too much HF pre-emphasis (leading to distortion), and no EQ at all results in too much HF noise and excessive groove excursions in the bass.
The RIAA curve we use today is a half-way house between the extremes. In the early Fifties, record companies had many different proprietary curves of their own, and audio magazines simply advised listeners to adjust the tone controls until the got the sound they wanted. Hifi enthusiasts and the equipment manufacturers demanded the record industry agree on a common standard, and the RIAA curve came out of that. The 45/45 Westrex stereophonic LP standard made a few years later was a similar industry-wide agreement.
This article is the kind of thing that is all too rare in audio writing; a serious technical article about one of the real pioneers in audio, with an extensive discussion of the technology of the day. Thank you, Ed Dell and Paul Stamler.
Thom Mackris, of Galibier Designs, pointed me to a 
