The CV531 (commercial 12C8) was designed for Radio/Radar reception and was issued in the late 1930's. The most usual multiple valve with a common cathode is the double diode triode. With a vari-μ pentode and double diode it gave the set designer flexibility to use this valve as final IF stage, AGC rectifier and detector or Detectors and first audio voltage amplifier.
The valve is electrically identical to the 6B8 except that the 12C8 was designed to operate from 12.6 Volt for the heaters. For use in vehicles where the 12.6 Volts were readily available from batteries.
The plain reverse.
For signal screening the control grid of the pentode is brought to the top cap.
The thin metal tube envelope is 25 mm in diameter and, excluding the IO base pins, is 63 mm tall.
References: Data-sheet, 1040 & 1043. Type CV531 was first introduced in 1939. See also1939 adverts.
