The CV233 is gas filled protective spark gap with a maximum breakdown voltage of 5.5 kV. The prototype was the BS5.
The KB/SL identifies this valve as being made to specification K1001 or K1006, the B denotes qualification by a UK authority and the SL identifies the maker as AEI, Leicester.
The CV designation on the base cap and a serial number on the glass. Inside there is an open cylinder of white ceramic.
The top electrode is positioned by the spacer resting on the ceramic.
The wide glass tube envelope is 30 mm in diameter and, excluding the IO base pins, is 60 mm tall.
