The CV1891 (commercially the 6B7) is a double diode output pentode for low cost local station receiver applications as detector, AGC rectifier and audio output.
The 6B7 design is of American origin as is the UX7 base design.
The KB/FB identifies this valve as being made to specification K1001 or K1006, the B denotes qualification by a UK authority and the FB identifies the maker as STC, Footscray.
The base cap is marked 6B7.
Below the screened pentode is a rectangular screening box that shields the two rod anodes that form the diodes.
The classic envelope is 38 mm in diameter, and excluding the UX7 base pins is 101 mm tall.
