Brimar was part of STC group and founded in 1933 to manufacture American pattern valves for the British market. Brimar stood for "British Manufactured American Radio" (valves). Valves were produced in the UK in various locations such as Foots Cray where it shared a site with Kolster-Brandes, another STC company. In 1960 Thorn Electrical Industries acquired the Brimar cathode ray tubes and valve business from STC and in 1961, Brimar became part of the joint venture between Thorn and AEI to manufacture and sell valves and cathode ray tubes. Brimar valves were produced and sourced from various factories across the world in later years. The Brimar name continued in Thorn Brimar and Thorn EMI Brimar. A facility at Middleton in Manchester was established in 1979 and ten years later Sidcup was closed and all design manufacture and testing moved to Middleton. In 1986, RET acquired Thorn EMI Brimar and the company was renamed Rank Brimar Ltd. The Rochester site was shut well before the merger with RET.
In 1996 Rank Precision Industries sold Rank Brimar together with sister companies Rank Taylor Hobson and Rank Cintel to a management buy-in (MBI) team. Finally in 1997, two new companies Brimar Ltd and Cintel Ltd were sold as a Management Buy Out process under a holding company called Image Precision International Ltd.
Brimar finally fell into administration in November 2012, blaming the economic climate and difficult trading conditions. However in 2013, Dermot Power, BDO business restructuring partner and joint administrator of Brimar, announced that they had completed the sale of the business of Brimar Limited, with a sale of the vision system display business to Image Precision Limited on 3 May 2013, and the Cathode Ray Tube and Long Range Thermal Imaging business to BAE Display Technologies Limited. (See also Rank Electronic Tubes)