What a good question! We may laugh today, but when I was a kid (in the late fifties and early sixties), my trumpet teacher and other studio musicians from the generation before us were constantly in envy of the Welk band members, who had to put up with LW's strict rules, bad temper and lack of humor, but got paid very well for it. It was *the* gig to have. Man, those guys actually owned their own homes! (My trumpet teacher was glad to be part of the Disneyland band as a part-time gig.)
Behind the haircuts, pastel suits and cheesy routines were some of the best musicians around. When I visit my folks and have to sit through it, I watch for "script smiles" (places where they're trying not to crack up at the corniness of it all). As camp, the show is still astonishing. Of course, it was never anything but sincere to Welk. Welk did a lot for music and musicians in his day.
I hope one of our knowledgable old-timers on this forum can answer your question about the mics they used. Also, I'd love to know what the rest of their recording equipment was like, what console they used, what medium they were recording to. Even though the music is dated and "light," you can still catch glimpses from time to time of how good his musicians were. Almost any one of them could have been in a major symphony orchestra or great jazz band.
Mark H.