Brimar (BRItish Made American Range) was a part of Standard Telephones and Cables Ltd (STC) and was founded in London as International Western Electric in 1883. From 1925 to mid 1980s the company was owned by ITT of the USA.

There is very little information available on how to read Brimar tube codes, but in general, they are one of the easiest to decipher.

The code consists of multiple sections and usually look like:
4G9/980 (4th week of production in July of 1959, tube type 6060)

BTW, if Brimar labeled tube doesn’t have the date code or it has foreign stamped on the tube, it’s not produced by Brimar, but by some other manufacturer. Many Brimar labeled tubes are actually Soviet made.

Deciphering different tube codes is hard even when they are in your own language. Deciphering Soviet tubes is even harder since the majority of information about them is in Russian.

Here is some information about common suffixes: