How to Decode Vintage Philips & Mullard Vacuum Tube Codes (Online Decoder Tool)

Every audiophile and vintage electronics enthusiast knows that commercial branding printed on vintage vacuum tubes can easily rub off or be counter-printed. Fortunately, Philips and its subsidiaries (Mullard, Valvo, Amperex, Dario, La Radiotechnique) introduced an infallible system in 1948: acid-etched codes directly on the glass envelope or base.

These etched batch and date codes allow you to identify the exact tube type, production revision, factory location, year, month, and week of manufacturing—regardless of what is printed on the glass.

Interactive Philips / Mullard Code Decoder Tool

Use our free online tool below to decode any Philips, Mullard, or Valvo tube code instantly. You can type batch codes like mC6 Δ6C, rX1 B2C3, or I63 B5D1:

Note: The application is case-sensitive. Please make sure to enter the code exactly as it appears etched on the valve.

Understanding the 2-Line Philips Code System

A standard Philips/Mullard code consists of two lines of small etched characters:

Line 1: Batch Code (Type & Design Revision) → e.g. rX1
Line 2: Date & Factory Code → e.g. B2C3

1. Line 1: Type Code and Revision

  • Type Code (2 or 3 characters): Identifies the exact tube model. For example:
    • mC = Long Plate ECC83 / 12AX7 (17mm plates, 1950s)
    • I6 = Short Plate ECC83 / 12AX7 (15mm plates, 1960s+)
    • rX = EL84 / 6BQ5 Power Pentode
    • GA = ECC88 / 6DJ8 Frame Grid Triode
    • A0 = E88CC / 6922 Premium Quality Dual Triode
    • KE / LK / xf1 / xf2 = EL34 Power Pentode variants
  • Revision Number: The digit following the type code indicates the design or batch revision (e.g., 1 for original release, 2 or 3 for minor factory engineering tweaks).

2. Line 2: Factory Symbol, Year, Month, and Week

The second line reveals the manufacturing origin and date:

  • 1st Character (Factory Symbol):
    • B = Mullard, Blackburn (United Kingdom)
    • Δ (Delta triangle) = Philips, Heerlen (Netherlands / Amperex)
    • D = Valvo, Hamburg (Germany)
    • R = Mullard, Mitcham (United Kingdom)
    • ≠ or # = Siemens & Halske, Munich (Germany)
    • L = M.B.L.E., Brussels (Belgium)
    • f = La Radiotechnique, Suresnes (France)
  • 2nd Character (Year Digit): Indicates the last digit of the manufacturing year (e.g., 2 = 1962).
  • 3rd Character (Month Letter): Letter A through L corresponding to January through December (A=Jan, B=Feb, C=Mar...).
  • 4th Character (Week Digit): Digit 1 through 5 indicating the week of the month.

Example Walkthrough: rX1 B2C3

  • rX = EL84 / 6BQ5 audio pentode
  • 1 = 1st manufacturing version
  • B = Produced at the Mullard plant in Blackburn, UK
  • 2 = Year 1962
  • C = March
  • 3 = 3rd week of March

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