Some valve/tube manufacturers put a cryptic code on the glass, in addition to the normal valve type and logo etc. The factory code is often etched into the glass, so may remain when the normal printing has been rubbed off. The codes used by Philips/Mullard/Valvo etc. are well documented on the web (for example, see Philips Code List), but there is little information for the codes used by Brimar and other Thorn group brands (such as UK Mazda and later Ediswan).
I have gathered together some Brimar codes here. Some are gleaned from the web - I have tried to give correct attribution. Others are from my own collection - there seem to be lots of Mazda valves around on eBay in the UK at present.
Anyone owning Brimar/Mazda valves will know that their factory codes tend to be harder to read than the Philips ones, and more easily smudged. In many cases the code is less resilient than the normal printing, but there will be times when the code may be the only way of identifying the valve type so a list will hopefully be useful.
The suggestion given here is not my own, but gleaned from a 2007 post on the Vintage Amps bulletin board - which sadly seems to have disappeared. A Brimar code consists of two parts. The first part is three characters, number-letter-number, which give the date of manufacture. The last number is the last digit of the year (so this suffers from the same ambiguity as the Philips code). The letter gives the month (A=January etc.), while the first number gives the week within the month. For example, 2C7 is the second week in March 1957 or 1967. However, I have a 6/30L2 (ECC804) which has a date code of 1N8 so are some letters omitted from the month code sequence, or is it more complicated than we think?
The second part is just a number, usually three or four digits long, which gives the valve type. Different versions of a particular valve type will have different numbers, although these may sometimes be grouped together. For example, 1573 and 1574 are types of ECC83 but so is 2162. It is suggested here that four digit codes started in the 1960s.
Between the two parts of the code there may be a slash /, or a space, or nothing at all. Sometimes it is difficult to distinguish a three-digit number preceded by a slash from a four-digit number with no separator, so there is some uncertainty in some of the four-digit codes starting with 1. For example, the code for ECC82 is said to be 1571 (see ref AA1), but I have some which are clearly marked 571. However, I have some 19AQ5 marked 660, and others marked 1660, so perhaps xyz and 1xyz are related (different factory)? Digits 5 and 8 can look quite similar. The code may be horizontal or vertical, and could occur at almost any height on the glass envelope. Sometimes it will be obscured by the normal printing.
|DPK||244||6BR7||CV2135||see 979, 8979|
|DPK||571||ECC82||12AU7||CV491||see also 1571|
|DPK||585||12BH7?||valve is unmarked but looks internally like a 12BH7|
|DPK||630||CV2212, 13D3||similar to CV4068, 6158|
|DPK||660||HL90||19AQ5||150mA version of EL90/6AQ5, see also 1660|
|DPK||977||E83CC||12AX7WA||CV4004, 6057||box anode, black, 1 flange, D getter - see 3977|
|eBay||979||6059||SQ 6BR7, see 244, 8979|
|DPK||1175 or 175?||6AK6|
|DPK||1291||PF818/EF812||7ED7/6EL7||30F5/6F23||30F5 and 6F23 are very similar, was one a mislabelling?|
|DPK||1426 or 426?||EZ90||6X4|
|AA1||1571||ECC82||12AU7||CV491, CV4003, 13D4, 13D5, 13D8||see also 571|
|DPK, VA1||1574||ECC83||12AX7||14mm plate|
|DPK||1576 or 1876?||ECC804||6GA8||6/30L2||I only have one of these; looks identical to 2195 version.|
|DPK||1660||HL90||19AQ5||150mA version of EL90/6AQ5, see also 660|
|DPK||1791||ECL82||6BM8||6PL12||pentode anode grey, staples facing out, no grid tabs, see 2242|
|DPK||1822||PL84||15CW5||300mA version of EL86|
|DPK, VA1||2160||ECC81||12AT7||black wing anode with rounded end|
|Oth||2161||ECC82||12AU7||14mm anode (branded Ediswan?)|
|DPK, VA1||2162||ECC83||12AX7||CV4004||14mm plate|
|DPK, JR1||2167||ECC88||6DJ8||see also 3910|
|DPK||2195||ECC804||6GA8||6/30L2||most of my ECC804 have this code|
|DPK||2242||ECL82||6BM8||6PL12||pentode anode black, staples facing in, grey heat tabs on control grid posts, see 1791|
|DPK||2563 or 2568?||30PL15|
|JR1||3910||ECC88||6DJ8||see also 2167|
|VA1,DPK||3977||ECC83||12AX7||CV4004, 6057||box anode, grey, 1 flange, O getter - see 977|
|DPK||3980||ECC81||12AT7||CV4024, 6060||SQ version, black single-flange anode with square end, sometimes triple mica|
|DPK||3981||6BW6||black anode, round getter, double support (see 1252)|
|DPK||3982?||QV03/12||6062||CV4039, SQ 5763|
|DPK||3986 or 3988?||EL821||6CH6||CV4055||see 1274|
|VA1, Oth||3987||ECC82||12AU7||CV4003||17mm grey plate, also seen on black half-box plate|
|DPK||8979||6BR7, 6059||CV4006, VX7081||SQ version? see 244, 979|
|Ref Name||Ref Location|
|AA1||Audio Asylum bulletin board|
|DPK||My own collection|
|JR1||Jogis Roehrenbude website|
|TC1||Virtual Valve Museum|
|VA1||Vintage Amps bulletin board|
|eBay||seen on eBay|
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updated 22 Aug 2018: modified for new website, note that Vintage Amps board has gone