Terry Kath with a pre-CBS Strat through an Acoustic solid-state amp and who knows what for speakers. I watch this concert every once in a while. I didn't get Chicago when I was a kid, it sounded hokey and big band and I was way into Hendrix, Van Halen, Rory Gallagher, Clapton and guitar fronted music. Chicago was something else with this line up and when 25 or 6 would come on the radio, they'ed chop the lead off so I never knew about the guitar parts. I don't think he could play a bad note with his style, it's as if he's talking. The equivalent of Yes, The Who, Led Zeppelin, ELP, and the other super groups of the day.
Terry blew his brains out when he was 31 years old.
You can look at the sun, just don't stare.
You can always have fun, just not there.