Essentially, the design of the head was based on linear Dynaco hifi amplification, more exacting and purposed differently than musical instrument amplification of the time. Add to that the use of KT-88(later 6550)power tubes, which I don’t think was common at the time. The cabs were unique as well; a proprietary, unusual design with angled port channels(but not a “folded horn” as it’s sometimes called, erroneously). Loaded with a pair of JBL D-140’s, which could more than handle the head’s peak output.
Yet, why is it that there are so many threads where someone complains that any amps on stage are too loud? I’m personally not down with the IEM thing, it’s too antiseptic and prophylactic for me, but my first real amp was a Sunn Sorado, a budget version of the 200s, then I moved to the real thing. I never had a problem keeping up with a drummer, let alone 20-50 watt guitar amps. If there was PA support(not common then), that would be gravy.
The current consensus here is that no guitarist should be working with more than 30 watts or so, but I don’t know how you could enforce that.