The 6B8 was designed for signal and AGC detection and first audio amplifier stage in superhet receivers. The glass tubular version is a later development in a smaller envelope. The electrically identical 6B7 is fitted with a UX7 base cap.
The grids are of wire and are supported on notched wire supports. This can be seen in the picture. The top cap can be seen connected to the inner of the wire grid supports.
The wide glass tube envelope is 28 mm in diameter and, excluding the IO base pins, is 74 mm tall.
References: Data-sheet, 1040 & 1043. Type 6B8GT was first introduced in 1937.
Absolute Maximum Operating Conditions¶
Updated January 29, 2013. shape:wide.glass.tube construction:pinch type:double.diode.pentode age:1930.1940 base:io heater:6.3v pins:8 pin:1.m pin:2.h pin:3.a pin:4.a(d2) pin:5.a(d1) pin:6.g2 pin:7.h pin:8.k pin:tc.g1