I first saw Zeppelin in '69, supporting LZ II, I believe. Semi-large concert hall in Chicago, on N Clark St...I forget the name of the venue, but it was large enough to host The Who, Zep, Joe Cocker, & many other of the larger acts of the day. LZ 's amps were miked. Later, as they became more famous, they graduated to still larger venues, all of which required the amps to be miked. The Acoustic (360 I believe it was called) was one of the largest & most powerful amps available at the time. But, just like today's 1500 watt monsters, large enough venues require everything to be miked, for a proper balance.