Dim Bulb Tester: What It Is, How I Built Mine, Seeing It In Action

Need tools? Here's a video showing what I use (with links!): https://youtu.be/MLK649c1_fM I get this question from subscribers here and there: What the heck is this thing? How does it work? Why do you need one? BETTER EXPLANATION OF HOW IT WORKS: https://www.youtube.com/watch?v=K9_MR7L0hrw Additional resources: https://antiqueradio.org/dimbulb.htm and https://audiokarma.org/forums/index.php?threads%2Fdim-bulb-tester-build-and-how-to.808399%2F