During the performance of "Get Back" (as seen in a now deleted YouTube video, different than the one I have below), you can see George Harrison turning his amplifier back on. I'm thinking Mal Evans most likely turned it off as he's seen talking to George during the song, probably telling him that they need to stop playing.
After the song, Paul McCartney says, "Thanks, Mo!" in response to the enthusiastic cheering and applause from Ringo's wife Maureen Starkey. Then John Lennon says, "I'd like to say 'thank you' on behalf of the group and ourselves, and I hope we passed the audition!" The dialogue can also be heard on the 'Let It Be' album.