Historical Question: Where did Tomorrowland 67's music broadcast from?

[Dumont]

I have read that on Disneyland's Peoplemover cars there were shortwave radios that transmitted BGM to the Peoplemover speakers. If that is the case, where did that music transmit from? One of the show buildings? Under the rocket tower/Peoplemover station? In Tomorrowland's service tunnel?

Also, what system did they use? At WDW, they used a version of Fidelipacs in the early years. I don't know if they had this same system in the 1960s.