Query Re "Kelly's Heroes"

[Richard Coutts-Smith]

One of my all time favourite movies, this has now been relegated to Sunday early afternoon veiwing times, which at least gave me the excuse to get out of a hot shed and in front of the A/C. while I try not to watch it with a critical eye, today saw me musing on Oddballs Shermans, leaving me with the very important, highly technical question that only MLU expurts can answer.
Oddballs tank is fitted with loudspeakers to create positive vibes while attacking, how does he play the music?? Assuming wire recorders were not in use then, the needle would have bounced of the '78, doubt if the local radio station would have been playing the required track.
Please come up with a satisfactory answer or I may have destroyed any future veiwings due to being a pedantic sod
Rich.