What was the first arena/stadium tour to use modern amplification?

My dad was probably just expecting something more loud and in your face. I’ll ask him more about his memories. I know he saw Zeppelin in Chicago in 1969. I’ll bet that one was loud

 

You are right, but two different although slightly the same stories. Bill Hanley: "When The Remains landed the gig of a lifetime backing the Beatles on their 1966 tour, the Boston sound engineer arrived unpaid and unannounced at Chicago Stadium. It was here where he convinced the band to use his equipment. As luck would have it, Beatles manager Brian Epstein heard the quality of The Remains sound system and hired Hanley on the spot; even inviting him to accompany the band(s) for most of the East Coast tour dates." Bill Hanley: The Father of Festival Sound - FRONT of HOUSE

Duke Mewborn: "By 1965 The Beatles had become used to being unable to hear themselves play. FB 'Duke' Mewborn, the boss of Atlanta hi-fi store Baker Audio, decided to give the group something that had never been done before: monitor speakers on the stage, pointing towards the group, to allow them to hear their voices and instruments.

It was adequate. We got over it, we were on top of it. You could hear them amidst the screaming.
Duke Mewborn
It wasn't just on stage that the sound was different. The state-of-the-art setup on the field included four Altec 1570 amplifiers, each giving 175 watts of sound, which in turn powered two stacks of Altec A7 speakers. Although unremarkable today, in 1965 it was an unheard of amount of power for a pop concert.

The difference was noted from the stage, with Paul McCartney exclaiming after She's A Woman: "It's loud, isn't it? Great!"

Being able to hear themselves enabled The Beatles to play tighter than usual, and they were delighted with the results. Afterwards Brian Epstein suggested that Mewborn deal with the sound for their other shows, but the offer was turned down." Live: Atlanta Stadium, Atlanta, Georgia

Here is the comment card from Brian that Duke solicited.

I have not gone through the blog where this is from but there is another good pic of the A7s, and the 1570 amps INSIDE BOB FOREMAN'S BRAIN PART 2: SEPTEMBER 2014 THE BEATLES



Edit 2: Finally to close this out, since it was bugging me the earlier Atlanta '65 Beatles pic you didn't really see if anything was directly in front of the stage, I forgot there is this pic, so nothing seemingly in front, so either any foldback monitor is behind the A7s, or perhaps the A7s were so loud they did the job relative to every other setup the Beatles had that year and the rest about the monitors is more lore.