> I didn't understand how they worked - I just followed the instructions
Indeed, Heath's instructions took a paint-by-numbers approach that did not offer analysis or explanation, so I have to disagree with hypertexthero that more than very basic theory was communicated. As for circuitry explanation, I found out the hard way on one occasion that I hadn't soldered a transistor properly, but there were no instructions on how to test for such a problem within the same "anyone can do this on a kitchen table" kit, so I mailed the board to Heath and they sent it back in working order for a small fee and postage. It is nevertheless a fond memory.
It’s been a looong time since I made a Heathkit (I think the last one was an oscilloscope in the 80s) but I do remember a theory of operation section in the manual, separate from the very clear assembly instructions. It’s true of the ones I randomly checked in the archive [0]. That said, the mail-in repair service for when things go sideways was a fantastic feature that not many kit companies had/have.
The first H-151 I built had a flaw. We went to the Heathkit store, about 45 minutes away, which provided the instructions for the fix. It was something like "scratch this trace off the circuit board and solder a wire between these two points."
Indeed, Heath's instructions took a paint-by-numbers approach that did not offer analysis or explanation, so I have to disagree with hypertexthero that more than very basic theory was communicated. As for circuitry explanation, I found out the hard way on one occasion that I hadn't soldered a transistor properly, but there were no instructions on how to test for such a problem within the same "anyone can do this on a kitchen table" kit, so I mailed the board to Heath and they sent it back in working order for a small fee and postage. It is nevertheless a fond memory.