Tube code

At the bottom of the glass of mainly European tubes is a code of 3 or 4 characters. This allows the manufacturer and the date of production to be determined.

For example, a Siemens EL34 from 1975 that I still have with the code B5A2 and the additional "change code" Xf3 above it.

According to the information I could find, these 4 characters refer to:
1 - Manufacturer
2 - Year of production
3 - Month of production
4 - Week of production

For tubes from the period before 1960, the code consists of 3 characters. The indication of the week is missing in that case.

1. Manufacturer code

I was able to find out the following list (probably not complete):

When a brand name is stated on the glass (or sometimes on the base), this will in some cases speak for itself. Keep in mind that these names don't always indicate who the actual manufacturer is. For example, a manufacturer of amplifiers can have tubes made with their own brand. You then have to find out where they were produced. You may come across tubes of the brand "Pope" that just come from the Philips factory (Pope = Productie Overschot Philips Eindhoven).

2. Year

Indicates the year. Difficult because it is only 1 digit Incidentally, there is still a code of 3 characters above the 4 characters described here,
the so-called "change code". With this, the period / batch in which the pipe was manufactured can sometimes be traced. If in doubt, it could be checked whether the tube is in the 60s or 70s
and whether, for example, the number 5 refers to 1965 or 1975.

If the 5 in the example refers to the date 1955, the code would not consist of 4 but of 3 characters.

3. Month

Is indicated with a character:

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


4. Week

The week number "within that month".

Undoubtedly, much more information can be found via the internet and the above is only a brief overview to get an idea of the underlying information of the codes.

NOS / NIB

Tubes deteriorate in use over the years, however, unused pipes will not really age. Many cries are "NOS" (new old stock) or unused tubes from an old stock. "NIB" (new in box) refers to an original production tube that is packaged in a (usually white / blank) box. Watch out for so-called "tests as NOS" offers, it concerns used or even new tubes and such a test does not exist.

New tubes are still being made in some factories, such as Sovtek, J&J / JJ, EH, EI / CVC and Svetlana. The moderate pipes from China are less appreciated.

Major brands have their own name on the tube and packaging. It is more difficult to determine from which factory these come.

Alongside an original Siemens ECC83 from 1976.

Tube type indication

The European type designation consists of letters followed by numbers such as the aforementioned EL34.