Inside a 1950s Vacuum Tube Computer: Bendix G-15

Restoration of the Bendix G-15 vacuum tube computer with magnetic drum memory begins by removing all of the circuit boards, removing the dust and grime of the ages, inspecting each for the usual problems of age (in particular, electrolytic capacitors that have lost their mojo), and making an inventory of each distinct circuit type. Each circuit type is described along with its schematic.

A remarkable fraction of the tube circuit modules in the computer are simple buffers whose only function is to amplify the outputs of logic modules to provide sufficient fan-out to drive the circuits to which they are connected. Germanium diodes are used wherever possible (principally in β€œOR” gates) to avoid costly vacuum tube logic.