The 6K7 and 6K7GT are 8-pin octal remote-cutoff (variable-mu) pentode vacuum tubes introduced by RCA in the mid-1930s. Engineered specifically for radio-frequency (RF) and intermediate-frequency (IF) amplifier stages in superheterodyne radio receivers, their variable-mu design allows effective Automatic Volume Control (AVC) without introducing signal distortion on strong local stations. The standard 6K7 features a rugged metal envelope for superior self-shielding, while the 6K7GT utilizes a compact T-9 glass envelope. Both variants feature a top grid cap to isolate the control grid, operate on a 6.3V heater, and fit standard 8-pin octal sockets. Available NOS and tested used.