Identify your tube

Engineers and hobbyists identify tubes by combining type number (on glass or box), structure (plates, getter, mica), and factory marks (date / plant codes). This page is a practical field guide — then look up the type in browse, the explorer, or search.

1. Read the type number first

Look for codes such as 12AX7, ECC83, EL34, or military CV numbers. American RETMA and European Pro Electron numbers are often electrical equivalents (e.g. 12AX7 ↔ ECC83). TubeDatabase links common equivalents on type and detail pages — still verify heater voltage, pinout, and max ratings on a datasheet before substituting.

2. Getters (the silver flash)

The getter is the reactive metal that keeps the vacuum hard. Its shape and support often date a construction era (US vs European progressions differ slightly).

• United States (oldest → newer): square getter → D getter → large O (halo) → small O (from roughly the mid-1960s).
• Europe (oldest → newer): foil getter → D getter → large O → small O.
• Support posts:single vs double ("goalpost" / cage) help separate families such as early Mullard long-plate ECC83 (mC1, f91) from later short plates.

Community chronology discussions (e.g. pinkfishmedia getter threads) are useful starting points; always cross-check against photos of known factory production.

3. Plate styles (and “carbon black plate”)

• Long black plate — roughly 1940s through mid-1950s on many US and early European dual triodes; prized for tone by some, more microphonic on average.
• Carbon black plate — plates coated or treated so they appear deep matte black (high thermal emissivity / secondary-emission control). Often discussed for premium 1950s RCA and similar constructions; not every dark plate is “carbon,” and not every carbon plate is labeled as such on the glass.
• Long gray plate — transitional late 1950s designs.
• Short gray plate — from about 1960 onward on many ECC83 / 12AX7 lines; lower microphony, more common today.
• Square plate (military ECC83 family)— often coded CV4004, CV492, B339, M8137; Mitcham ("R") and later plant codes appear on date marks.

4. Factory and date codes (high level)

Plants printed short codes for factory and date. Exact tables fill multi-page PDFs; the patterns below help you know what to look for:

• Philips / Mullard family— three-character style codes (e.g. plant letter + year/month digits). Blackburn often "B", Mitcham "R" in period discussions. Public code lists are maintained by collectors (Philips code lists, Mullard decoding guides).
• Telefunken— diamond / <> marks and date codes on base or glass; factory and period decoding is documented on specialist sites (e.g. tctubes.com Telefunken notes).
• US makers (RCA, Sylvania, GE, …) — etched or inked date codes; black-plate + D-getter combinations are classic late-1950s RCA 12AX7 cues.

We link out rather than republishing full copyrighted code tables. Prefer primary datasheets and established decoder PDFs when dating a valuable bottle.

5. Country and rebrand marks

Boxes and glass often disagree: a brand (Telefunken, Amperex, Valvo) may be a rebrand of another plant (RFT, Philips Heerlen, etc.). On TubeDatabase, manufacturer vs brand fields separate that when the data is known. Country of origin may appear as a code or printed name — treat it as a clue, not a complete pedigree.

6. White top = usually dead

If the getter flash has turned milky white across the top of the envelope, the tube has typically lost vacuum (air leaked in; getter exhausted). That is a common “broken tube” visual — not a manufacturing style. Do not confuse with intentional white ceramic bases or printed labels.

7. Mullard ECC83 field notes (worked example)

• mC1:~17 mm long plates; square/cage getter on two supports; copper posts — classic early long-plate sound, higher microphony risk.
• f91:~1957–early 1959; 17 mm plates with halo getter on double goalpost support (unusual combo). Short production window.
• Later short-plate designs traded some “size” of sound for lower microphony and higher yield.

Often-cited reference constructions

• RCA black-plate 12AX7 with square/D getter, late 1950s.
• Early Blackburn Mullard long plates vs later IEC/Mullard short plates (many prefer earlier for tone; later are more common).

Next steps on TubeDatabase

• Search by number or brand.
• Explorer for parameter filters (µ, Rp, heater).
• Submit photos and notes for missing variants.

Attribution: community decoder discussions and classic datasheet practice inform this summary. For full plant code tables see collector-maintained Philips/Mullard/Telefunken references and manufacturer datasheets — TubeDatabase does not claim every historical code combination.