The CV138 UK prototype was the X138 and subsequent commercial designation was the 6AM6, however the most usual Type designation for this valve is the EF91. It was (almost) the universal amplifier pentode of the early post war era, many manufacturers made versions of this standard valve. The version shown here was made by Brimar and is labelled for service use.The original CV138s were made in the US in the mid 1940s. UK production was all post war.The valve is a high gain, high impedance, sharp cut-off, screened pentode. It could be used from AF to VHF up to about 200 MHz and was found in large numbers in most types of electronic equipment. In radio it was used for RF and IF amplification, for oscillators and frequency multipliers.The electrodes are hidden by the coating on the inside surface of the envelope. This coating was designed to eliminate gas being released from the glass under electron bombardment. The anodes are small and electrons can escape.
Made in England.The thin glass tube envelope is 18 mm in diameter and, excluding the B7G base pins, is 46 mm tall.References: Data-sheet & 1040 Type CV138 was first introduced in 1941. See also 1941 adverts. |
