The CV1991 is electrically equal to the 6SQ7 but the specification is for the Glass Tubular version 6SQ7GT. It is a double diode triode sharing a common cathode.
The triode is seen at the top with the carbonised anode, the double diodes are seen as the bright anodes between the triode and the pinch. One diode anode is the box and the other is formed from the two vertical rods.
The KB/T identifies this valve as being made to specification K1001 or K1006, the B denotes qualification by a UK authority and the T identifies the maker as British Tungsram, Tottenham.
The triode at the top and below is the screening box shielding the two rod anodes for the signal diodes.
A closer view.
The metal skirt has separated and adhesive tape is holding it in place.
The wide glass tube envelope is 29 mm in diameter and, excluding the IO base pins, is 70 mm tall.
References: Data-sheet, 1040 & 1043. Type CV1991 was first introduced in 1939. See also1939 adverts.
