Records tell me that he was the San Francisco branch manager of Brunswick records in 1924. There is some debate if this is the same C.P. MacGregor... Due to the location, and the experience curve I'm going to make the assumption that it is. Every incarnation of the MacGregor company was in this region, and it just makes sense.
MacGregor was a prolific producer and distributor syndicated transcription discs. He did the Shadow, Cecil and Sally Eps, AFRS programs, Al Jolson, Jubilee, Lux Radio theatre, The Hollywood Theatre, Eb and Zeb, and sessions with Leadbelly, Charlie Parker, Stan Kenton... hundreds of others. There is no end to the catalogs if you Google his name. the predecessor to Capitol Records, Liberty records recorded in their studios in the 1940s.
In the book On The Air, John Dunning wrote:
"He argued that transcriptions enabled him to produce flawless shows, losing the excitement of live performance was a small price to pay."The first of his companies, MacGregor and Ingram Co. was incorporated about 1929. Some of their records of this era bear the call letters of KFRC-AM. That's 610 in San Francisco and they were a customer at least as early as 1932. Interestingly, The KFRC Anson Weeks program with Walter Bunker, Jr. announcing were all recorded at CPM demonstrating a strong business connection. In that year the company changed its name to MacGregor & Sollie, indicating a change of partners. That incarnation, located on 865 Mission Street, survived until 1937. I have no idea what happened to Mr. Sollie, but C. P. MacGregor continued on solo into the 1970s. I have no proof but I suspect this coincides with his death.
MacGregor & Sollie promoted their San Francisco transcriptions as “Hollywood”-style dramas, capitalizing on the screen backgrounds of veteran actors like Carl Kroenke. stations from coast to coast contracted with MacGregor & Sollie at $17.50 for each episode. By 1945 the C.P. Macgregor studios had moved to a more upscale neighborhood: 729 South Western Avenue, Hollywood, CA. In that era they were using 16" transcription discs.
They had competition of course. Westinghouse was the largest of these. Their World Broadcasting transcriptions are a common sight. WBS discs were pressed on red acetate or vinyl and were more often music programs.
Today the Library of Congress has possession of the MacGregor collection. The surviving masters and recording ledgers of all three companies, MacGregor and Ingram, MacGregor and Sollie, and C. P. MacGregor are at least preserved.