B7G base
The 7-pin B7G tube base was developed in the late 1930s for miniaturized all-glass tubes. The earliest tubes using this base were commercially introduced in 1939, such as the 6J6.
The pins are arranged evenly in a circle of eight or ten evenly spaced positions, with one pin omitted; this allows the tube to be inserted in only one orientation. The pins are stiff wires protruding through the bottom of the glass envelope and plug directly into the socket; the base is an integral part of the glass envelope. The pinched-off air evacuation nub is at the top of the tube.
B9A is the most common base for tubes from the 1940s to the 1960s.