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The CV1981 (commercially the 6SK7) is a variable μ pentode for RF and IF amplifiers in superhet receivers. The gain of the device being controlled by a negative voltage derived from rectifying the final IF signal. In this way strong signals do not overload the receive chain because the various controlled stages have their gain reduced.

The reverse of the steel envelope is plain protective black paint. Stamped into the base of the envelope is 6SK7.

The thin metal tube envelope is 25 mm in diameter and, excluding the IO base pins, is 51 mm tall.

References: Data-sheet & ¹⁰⁴⁰. Type CV1981 was first introduced in 1938. See also 1938 adverts.

Pin Connections

Absolute Maximum Operating Conditions^¶

Thanks to Frank Philipse for supplying the above PDF datasheet.