The 6J8 (primarily produced as the glass 6J8G variant) is an 8-pin octal triode-heptode vacuum tube introduced in the late 1930s for superheterodyne radio receivers. Designed specifically for converter and local oscillator/mixer applications, it combines an oscillator triode section and a signal-receiving heptode section within a single envelope to minimize frequency drift and cross-modulation at high frequencies. Featuring a top grid cap for high RF isolation on the signal control grid, it operates on a 6.3V heater and fits standard 8-pin octal sockets. Available NOS and tested used.