The 6A8 is an octal-base pentagrid converter designed for local oscillator and mixer service in superheterodyne radio receivers. Originally introduced in metal-envelope construction (with Pin 1 connected to the metal shell for internal shielding), it was also produced in glass variants including the shoulder-style (ST-12) 6A8G and compact tubular (T-9) 6A8GT. Operating on a 6.3V/0.3A heater, it combines frequency conversion and oscillator functions into a single stage and features a top grid cap for control grid connection. It was widely specified in mid-to-late 1930s console and tabletop receivers manufactured by RCA Victor, Zenith, Philco, Crosley, and General Electric. Available in NOS and tested used conditions.