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.

The Brimar “T” Yellow Label

In addition to the etched date codes, you will frequently encounter Brimar tubes—particularly from the late 1950s and 1960s—featuring a prominent yellow “T” logo on the glass. This was not a decorative choice; it signified a specific grade of vacuum tube designed for high-reliability applications. The “T” stands for Trustworthy. These were Brimar’s “Special Quality” (SQ) valves, engineered to be more robust than their standard commercial counterparts. They were the British equivalent of the American “Ruggedized” or “Premium” lines (like the GE Five-Star or RCA Command series).

Date codes have:

• The first number is a week of production
• The second number is a month of production
• The third is a year
• / (Slash separator)
• Tube type

First number – week of production:

1. week 1 of production month
2. week 2 of production month
3. week 3 of production month
4. week 4 of production month
5. week 5 of production month

Second letter – month of production:

• A = January
• B = February
• C = March
• D = April
• E = May
• F = June
• G = July
• H = August
• I = September
• J = October
• K = November
• L = December

Third number – year of production:

Forth number – tube type:

3 digit code shows pre-1960 production, 4 digit code shows that a tube has been produced after 1960. This, combined with the third number can determine exact production year.

Also take a look at Brimar Special Type tubes