The 6K8 and 6K8GT are 8-pin octal triode-hexode converter vacuum tubes introduced by RCA in the late 1930s. Designed specifically for local oscillator and frequency converter service in shortwave and all-wave superheterodyne radio receivers, the triode and hexode sections are internally coupled to provide exceptional oscillator stability and minimize frequency drift at higher radio frequencies. The standard 6K8 features a durable metal envelope for built-in RF shielding, while the 6K8GT utilizes a compact T-9 glass shell. Both variants incorporate a top grid cap for high isolation on the RF control grid, operate on a 6.3V heater, and fit standard 8-pin octal sockets. Available NOS and tested used.