acorn tube: a small vacuum tube; used at high frequencies
tube: electronic device consisting of a system of electrodes arranged in an evacuated glass or metal envelope
council of trent: a council of the Roman Catholic Church convened in Trento in three sessions between 1545 and 1563 to examine and condemn the teachings of Martin Luther and other Protestant reformers; redefined the Roman Catholic doctrine and abolished various ecclesiastical abuses and strengthened the papacy