This exhibit is laboratory sample of the 6AF4A from Brimar. Probably these were made as pre-production devices for distribution to manufacturers for testing.
The 6AF4A was designed for TV service as a UHF oscillator in front-end mixers. Typical frequency of operation would be 0.95 GHz.
The /FD identifies the maker as STC, Rochester.
The reverse carries the UK Government specification of CV5074 as well as the /FD. The pins are gold plated.
The anode is shaped so that on each side of the grid/cathode assembly there is a small flat working face backed by a rectangular channel to carry away the heat produced.
With the microscope the grid becomes clear.
The thin glass tube envelope is 18 mm in diameter and, excluding the B7G base pins, is 36 mm tall.
References: Data-sheet & Data. Type 6AF4A was first introduced in 1954. See also1954 adverts.
