The 20CV is a vacuum photocell that is most sensitive to near infra-red radiation. This makes it most sensitive to incandescent light bulbs. The cathode is caesium on oxidised silver.
The 20CV photocell has a B8B (aka B8G) base but only four pins are present. The construction is an early form of the pressed glass disc to hold the electrodes. The pins are extensions of the electrode supports. The pressed glass foot was first used by RCA in 1935 for their metal valves and the B8B or Loctal base was introduced by Sylvania in 1938.
The semi-circular photocathode would release electrons in proportion to the light intensity reaching the cathode. The rod anode would be held at about 90 Volts positive of the cathode to collect the photoelectrons.
The wide glass tube envelope is 29 mm in diameter and, excluding the B8B base pins, is 62 mm tall.
References: Data-sheet & 4034. Type 20CV was first introduced in 1949. See also 1949 adverts.
Absolute Maximum Operating Conditions¶
PDF scanned from an original document held by the museum
Updated January 05, 2022.