The ECC85 is the definitive double triode for the front end stages of FM radio receivers. It was designed specifically for the purpose and released in 1954. This exhibit has plain white lettering and is marked as British Made.
It was popular in the late 1950s to add an FM radio board to a television receiver as well as to make dedicated Band II receivers.
The two independent valves are screened by a rectangular plate across the diameter of the envelope. One triode would be used as an RF amplifier and the other as the local oscillator. The oscillator would be run 10.7 MHz lower than the incoming signal, and in the mixer a standard 10.7 MHz IF would be produced.
One triode seen face on with the intersection screen beyond.
The screen extends above and below the mica discs that hold all of the electrodes in place.
The thin glass tube envelope is 20 mm in diameter and, excluding the B9A base pins, is 48 mm tall.
References: Data-sheet & 1040. Type ECC85 was first introduced in 1954.