I have been restoring vintage VTVMs (most of them being by Heathkit) over the last several years, and have gathered a fair amount of experience and knowledge about them and their workings. I decided to put most of that into this single video documentary in order to share it with others. I also include complete details on how to make a suitable battery eliminator that works well with the Heathkit lineup of VTVMs.
The latter 2/3 of the video features my newly CAD drawn schematic/documentation package, and the PDF of that may be downloaded here:
https://www.serpentwebsite.com/fileshare.htm
with the IM-18 link near the bottom of the page
Here is a timeline table of contents for this video:
00:00 Introduction & history
05:48 Opening the typical Heathkit VTVM case
06:21 Internal overview
12:06 Restoration (things that commonly need attention or replacement)
19:09 Battery eliminator
29:58 Vacuum tubes
33:34 Test leads
35:05 Calibration
46:35 Schematic diagram & circuit theory