In this case, I felt compelled by a pile of tube-related parts I had harvested after ripping an old 500-series Tek scope apart, a wish to play with test tube circuits (test-tube circuits?) on the bench with a handy bench power supply built just for this purpose, and not much else to do. In order to construct some tube circuits on a “breadboard” style set up and be able to manipulate or dial-up the supply voltages at will, I would need to have a bench supply that would put out low as well as high voltages, not to mention grid bias voltages, filament power and would display what those voltages were. Being able to also display the current drawn from any of those would be a bonus. It might also look pretty cool.
As I said I wanted to put together circuits that were “breadboard” style, sort of like those awful-but-ubiquitous (don't get me started) white push-in proto-boards that you see everywhere anybody is messing around with electronics. But for tubes. At least as far as capability goes; I don't really mean to use those white things for circuits with 350 V floating around them. But the breadboard part is for another instructable and not covered here.
By the way, the term “breadboard” comes from the 1920's and 1930's when young people were just getting into an exciting new thing called “radio”. They were building their own crystal radio receivers from scratch and when they needed a platform to mount coils and cat-whiskers and such to, the handiest way to do it many times was to “borrow” a real honest-to-goodness bread-cutting board from Mom's kitchen, sometimes when she wasn't looking. I'm just guessing, but She probably wasn't too impressed. Yeah, hackers existed then, too, and the term just stuck.
I also assumed that I would need to build it for minimal cash outlay, hence the old tube-based scope.
First, my source of parts...