Chamber of Chills #6 is a digest-sized reprint of Chamber of Chills #1.
There are minor differences - the title banner at the top of #1 has been omitted; there is a yellow background filling up blank space above the title; and the advertisement on the rear cover is for The Amazing Spider-Man series, not the Avengers. Otherwise it is a facsimile of the first issue.
There are a few years between these issues - Chamber of Chills #1 is from 1977 with a $0.50 cover price, #6 from 1980 with a $0.60 cover price.
Interestingly, The Amazing Spider-Man also sold for $0.60 at this time, but was still published as a full-size series.