[David] runs this computer with two power supplies of +24 and -12 VDC, rather than the hundreds of volts typically used in vacuum tube designs. The modules are constructed on single-sided copper ...

For most of us, vacuum tubes haven’t appeared in any of our schematics or BOMs in — well, ever. Once mass-manufacturing made reliable transistors cheap enough for hobbyists, vacuum tubes ...

The telephone company had problems with vacuum tubes, too, and hoped to find something ... but not as well as a conductor such as copper) had been tossed about before World War II, but knowledge ...

and the tubes are twin Raytheon JAN6418 MIL-SPEC vintage vacuum tubes. According to Astell & Kern the copper here isn't just cosmetic: it says that the metal was chosen for its "outstanding ...