The first Boeing 747s (-100s and 200s) had a small hump behind the upper deck that was covering some antenna.
On nearly all early Jumbo Jets this "second hump" was replaced in the late Seventies. Only very few of them were carrying that antenna cover after 1980. But I remember I´ve seen an old PIA Pakistan 747 two years ago still flying with it.
Does someone know from which line number or year they abolished that cover and why? Must have been some time in the early 70s I think.