The 6H6 is a metal-envelope twin diode vacuum tube introduced by RCA in the mid-1930s for detector, automatic volume control (AVC), and low-current rectification duties in superheterodyne radio receivers. Featuring two completely independent diode units with separate cathodes and plates sharing a common heater, it provides excellent circuit flexibility and low-interelectrode capacitance for detector and noise-limiter applications. It operates on a 6.3V heater and fits standard 8-pin octal sockets. Available NOS and tested used.