I have a number of RCA classical recordings from the '50s. From Wiki:
On October 6, 1953, RCA Victor held experimental stereophonic sessions in New York City's Manhattan Center with Leopold Stokowski conducting a group of New York City musicians in performances of George Enescu's Roumanian Rhapsody No. 1 and the waltz from Tchaikovsky's opera Eugene Onegin. There were additional stereo tests in December, again in the Manhattan Center, this time with Pierre Monteux conducting members of the Boston Symphony Orchestra. In February 1954, RCA Victor made its first commercial stereophonic recordings, taping the Boston Symphony Orchestra, conducted by Charles Münch, in a performance of The Damnation of Faust by Hector Berlioz. This began a practice of simultaneously recording orchestras with both stereophonic and monaural equipment. Other early stereo recordings were made by Toscanini (never officially issued) and Guido Cantelli respectively, with the NBC Symphony Orchestra; the Boston Pops Orchestra under Arthur Fiedler; and the Chicago Symphony Orchestra under Fritz Reiner. Initially, RCA used RT-21 quarter-inch tape recorders (which ran at 30 inches per second), wired to mono mixers, with Neumann U-47 cardioid and M-49/50 omnidirectional microphones. Then they switched to an Ampex 300-3 one-half inch machine, running at 15 inches per second (which was later increased to 30 inches per second). These recordings were initially issued in 1955 on special stereophonic reel-to-reel tapes and then, beginning in 1958, on vinyl LPs with the "Living Stereo" logo. RCA has continued to reissue many of these recordings on CD.[16] Another 1953 project for RCA was converting the acoustically superior building Webster Hall into its main East Coast recording studio. RCA operated this studio venue from 1953 to 1968.