The Compactron marked the end of the Vacuum Tube Era

The writing was on the wall that vacuum tubes were becoming obsolete while solid state components, such as transistors and diodes, were taking place of many vacuum tube applications.

In 1961, for one last fanfare, General Electric introduced the Compactron, a vacuum tube family to compete with solid state diodes and transistors. The idea with the Compactron was to integrate several vacuum tube components (Diodes, Triodes and Pentodes, oh my!) into a single glass envelope with all components sharing the same filament, thereby, lowering power consumption and the amount of heat generated. Two identifying characteristics of a Compactrons are a 12-pin footprint and evacuation glass tip located at the center bottom instead of the top of the vacuum tube.

While the Compactron never fully stopped the onslaught  of the transition to solid state diodes and transistors in the electronic industry, it did carve out a niche market being used in many low cost hybrid (using both solid state and vacuum tube components) portable color televisions of the 1960s until mid-1970s. The Compactron was used in high voltage, or high current circuits applications where early solid state diodes and transistors were not suitable. 

Eventually solid state diodes and transistors technology became more mature and new lines of these solid state components were designed for high voltage/current applications taking the place of  Compactrons.  Compactrons were completely phased out of new electronics by 1986 but had a good run of 25 years!