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This is called an IBM Puggable Unit using a vacuum tube and supporting electronics for computing machines of the late 1948s. This was a new and revolutionary idea of the era. In 1948 IBM announced the 604 Calculating Punch Machine that used a revolutionary internal circuit called a “Pluggable Unit” for NOT, AND comparison logic and mathematical calculations that could quickly be removed if it failed and new replacement inserted. Prior machines often times failed and would take many hours, days and even weeks to repair. That is because supporting circuitry for the Vacuum Tubes was internal to machine and NOT easily repaired. The IBM 604 and later machines could have as many as 1,400+ tubes and it was important to diagnose point of failure and easily swap out failed Pluggable Unit with new Unit. This treasure has IBM tube (tube marked 2D21 and TR-2) with three levels of supporting electronics (Tube, and 2 levels of electronics). Size 5” in length. We have seen Ebay auctions with prices nearing $ 300.00+ for this museum treasure. These 50+ years old Pluggable Units are rarely found as most are now in museums. This is a very rare treasure of computing history and belongs with a serious collector or computer museum.
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