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 been re-branded by the re-seller Bentley.
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.
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.
One triode section with the screen behind. The grid is wound on copper rods for good heat dissipation and the heater has been twisted together before being inserted into the cathode. This is a hum reduction technique.
The thin glass tube envelope is 21 mm in diameter and, excluding the B9A base pins, is 46 mm tall.
References: Data-sheet & 1040. Type ECC85 was first introduced in 1954. See also1954 adverts.