I'm a sucker for an old piece of hardware... A regulated power supply providing 3 rails: 0-400V 100mA (B) 0-100V 1mA (C) 6.3 VAC 4A It's nicely made, but pretty clearly not a commercial unit. The meters measure either the B or the C output. However there is no deflection of the current meter on the C output (maybe because 1mA wouldn't show up, maybe because it doesn't switch it over). However there's plenty of room above the existing meters to add a smaller pair of meters, and maybe even some pots to add current limiting. The case seems to be of some sort of bolt together construction, possibly also custom made. Are you expecting to find a heatsink on the back? Oooh, no... it has those vacuum tuby thing in it! Let's take a closer look. That's a pair of 6L6GC's you can see there. At this point I don't know if they are in parallel or there is one for each output. These tubes are rated for an anode voltage of 500V and a forward current of 0.9A, so a single tube could handle the load. But why would you use one of these for 100V and 1mA? A view from the top shows you the other valves There's more evidence here that this is a custom or possibly home-made construction. The vintage of the transformer on the left doesn't seem to match some of the other stuff, but I may be wrong. The two outer 7 pin valves are OA2's, and the middle one is a 6BH6. The OA2 is a regulator tube with an operating voltage of 150V and current of 5mA to 30mA. Why are there two of these? And given the low current from the 100V output, would you really have a regulator tube drawing at least 5 times the maximum output current? The 6BH6 is a pentode, and I guess this could be the output tube for the 100V supply, or it may be for something else. Looking underneath, it's nice and clean: You can really see this was finished off by hand -- look at the mounting holes for the two caps that are mounted on the upper side of the chassis. Obviously there are lots of semiconductor diodes here, and apart from the construction, I think the thing that most dates it are the ELNA capacitors. I have checked the basic performance of the outputs, both vary smoothly in the range expected, but the 6.3VAC is closer to 7.5VAC. I have also loaded the 100V output to 1mA, and here things got surprising. The voltage sagged by about 20V when this load was applied. It may be that the output has a high impedance to protect the grids it may be connected to (if you make a mistake) or it may just be that the regulation is poor (or maybe non-existant). I have yet to load-test the other outputs, but that's on my radar. Also, I'm going to reverse engineer a schematic so I can see what's actually happening.