The Heathkit SB-620 “Scanalyzer” is an IF spectrum analyzer. It graphs the amplitude of signals around the one that your receiver is looking at, so you can see all of the signals around you at a glance. Problem is, it has to be setup for the particular IF frequency of your receiver. The original kit included parts for a wide range of IF frequencies. Only one frequency could be installed though and my unit had the wrong frequency for the classic Heathkit SB-301 receiver I have.
The pdf article describes how to convert it to the IF frequency common to many Heathkit receivers, including: SB-100, SB-101, SB-110, SB-102, SB-104, SB-300, SB-301, SB-303, HW-100, HW-101 and HW-104. The photo above shows it operating with actual 80m signals. Get the article and schematic below: