How to Read Mullard & Philips Tube Codes

01 / Look first

Find the small code—not just the big label.

Check the lower side of the glass, near the base, and the bottom of the tube or its base, where the construction allows. Some codes are etched or otherwise permanently marked on the glass; the historical Philips reference also illustrates codes applied to the bases of different valve styles. The type and production groups may be on two short lines, or arranged differently around a base.

1. Record the large printed brand and type exactly as seen, such as Mullard ECC83 or Amperex 12AX7. That is the marketed identity, not a factory certificate.
2. Locate the smaller type / change group and the factory / date group. Photograph both and preserve spaces, symbols, uppercase and lowercase letters.
3. Check whether the layout is the old system or the new system. Do not decode an old month symbol with the new month chart.
4. Read factory, date and type together, then cross-check construction, packaging and any original printed markings before making a firm identification.

02 / Understand the arrangement

Two groups, two different jobs.

The reference uses six letter labels for what each position means. T identifies the tube type; C is a change/batch symbol; F identifies manufacturer, factory or—in some bought-in production—country of origin; Y is the last digit of the production year (new codes only); M gives the month; and W can give the week of that month. These letters are placeholders in the diagrams, not the markings you should expect to see literally.

Physical position varies. The original diagrams show the old code on glass envelopes and on valve bases, with the groups sometimes separated, reversed or positioned around the bottom. The new code has a common TTC / FYM or TTC / FYMW arrangement, but the reference also documents FYM / TTC and W F Y M layouts, including examples from Brazil, Australia and Eindhoven. Read the roles of the characters; do not assume that the top visible row is always the same group.

03 / Old-code method

Old codes: the month changes with the year cycle.

The old system used a T…C type/change group and an FM factory/month group. The month symbol repeated every three years. To resolve the year, use the change character's three-year sequence together with the old month character. The chart below reproduces the underlying relationships in a new reader-friendly layout.

Old month symbols (do not use the A–L new-code chart here)

Old change/batch symbol cycle

The three rows in the historical table are sequences for 1948–50, 1951–53, and 1954–56. The symbol is not a simple year number. A blank in the later rows below means the reference does not specify an entry for that sequence position.

The Philips reference notes an earlier numeric type-identification system and that Mullard adopted the later format around 1955. The historical transition is not an exact universal cutoff for every factory.

04 / New-code method

New codes: read factory, year digit, month and (sometimes) week.

In the typical newer arrangement, the type group is T…C; the production group is FYM or FYMW. The year digit alone does not identify the decade: 4 may indicate 1954, 1964 or 1974 depending on the factory, type and other evidence. For the documented yellow-print examples below, the survey establishes the 1960s context.

New-system months

05 / Where was it made?

Factory symbols, origin and the printed brand.

Read the F position in the correct production group, not an isolated letter somewhere else on the tube. This expanded directory retains the historical reference's multiple assignments where a symbol was reused or applied to purchased-in tubes. Letter case, period and adjacent code characters matter.

This is a broad, reader-oriented selection of the source's factory/origin list, not a verbatim or exhaustive reproduction of every unusual graphic symbol. Some printed symbols do not render consistently as plain text; do not equate an unfamiliar etched mark to a letter simply because it looks similar in a photograph. Consult the complete visual factory table if the mark is unusual.

06 / What tube is it?

Search the type-code index.

The other line is often the best clue when the large commercial type designation is worn away. The type code can be one, two or three symbols; the single-symbol group in the historical list applies to B7G tubes. A further change/batch character may follow it, so do not treat every character of the upper line as part of the tube type.

The entries below are selected, useful identifiers re-arranged from the Philips reference. They are not every entry in its extensive type register. Some tube types have multiple type codes or changes in construction; in other cases a code has more than one listed application.

Search ignores letter case; the codes in the results retain their original capitalization.

69 selected entries shown.

07 / Mullard yellow printing

Yellow ink is interesting. The etched code tells the manufacturing story.

An earlier photographic survey of yellow-printed Mullard valves found decoded manufacturing examples spanning 1962 to 1965. That is the range observed in its sample, not proof of the complete production period, and yellow printing alone is not a test of condition, originality or sound quality.

Observed manufacture-date suffixes in the historical yellow-print sample

These are transcribed from the survey's tabulation on its fourth page. They show reported specimens, not continuous production, production totals or a complete census. An asterisk indicates an incomplete character in the survey.

Examples by tube type in the photographic survey

The survey also includes specimens bearing D4F1 and Z4G*. A Mullard-branded yellow example therefore should not automatically be described as Blackburn-built. The individual construction, marking and full code determine the origin claim.

Reference and research note: This is an original, reorganized reader's guide based on Philips Factory Valve Codes, revision 7 (17 May 2005), especially its introductory legend, old/new code application diagram, factory symbols and type-code sections, together with a separate historical photographic survey of Mullard yellow-printed valves. Some listed codes have more than one assignment; ambiguous symbols and the limits of the sample are stated rather than silently resolved. The source documents contain more codes and exceptions than this web-page selection; consult the complete historical code register for uncommon types and difficult symbols.