Vacuum tubes were used on the third version of the DeLorean time machine, after Emmett Brown and Marty McFly recovered it from the Delgado Mine in 1955. In order to replace key parts from 1985 that would have existed in 1955, including the destroyed time circuit control microchip, Doc worked from the schematic diagram included with the repair instructions to fashion a boxframe unit that was attached with straps to the hood of the car, which included a vacuum tube assemblage that helped control the time circuits.