Of course, he totally missed the concept of a dim bulb
tester.

Nobody said he was a tech, so you're probably right. But the thing does act as a rheostat.

I think it could come in handy for tube equipment. There are also those Sony amps with the VFETs that will fry on a DBT.

I was thinking about when you have lots of current overhead, like lighting the filaments of a bunch of tubes. The bulb would probably go across the liquistat. (add to spellcheck) Then even on solid state ones you can laeae the stat open and run through the bulb, When you want to crank it up and see how it does on more power, the light gets bright of course, this is where you would engage the liquistat. That would be good on a receiver or amp with remote control because the line voltage to it might get too low and then the damn thing shuts off.