| System | Period | Rows | What it dates |
|---|---|---|---|
| Sugden A21 variants: Richard Allan badge, Series 2/3, A21a, A21SE, Signature | 1967-2015 | 9 | The Richard Allan badge is the trap: those units are 1967-1968 Sugden builds sold under another maker's name, and they are the earliest A21s. A 'Sugde |
| Sugden factory eras (research, Cleckheaton, Heckmondwike) | 1967-2023 | 3 | Factory eras bracket a unit but do not date it: Cleckheaton covers the 1970s, Heckmondwike 1981 onwards. Useful for a provenance note, useless as a ye |
| Sugden Class A heat (safety, not dating) | whole A21 production | 1 | No manufacturer temperature figure is published for the A21; the general Class A statement and the Musical Fidelity A1 measurement in the universal fa |
| Sugden official reference (history, ampography, how-old-is-it) | 1967-present | 2 | A pointer to the source that holds the table. Nothing is read from the number itself. |
| Japanese capacitor date codes - pointer to the universal layer | whole vintage period | 0 | Not duplicated: component codes date the part, not the unit. |
| Hunts capacitor date code (WHITSUNDAY) | 1950s-1969 (Hunts taken over by Erie in the late 1960s, probably 1969) | 25 | Dates the CAPACITOR, not the unit: it gives a terminus post quem. the source notes that nobody knows how long new capacitors sat on stockroom shelves, |
| British year-letter date codes (TCC, Dubilier, Radiospares, Woden, Welwyn) | 1950s-1960s | 4 | Dates the component only. Welwyn codes this way ONLY on wirewound resistors ('only wirewound resistors have date codes'). The characters before the co |
| Mullard 'mustard' capacitor date code | late 1963 onwards (used occasionally in late 1963, more frequently from mid 1964) | 3 | Dates the capacitor. It says nothing about the unit other than a terminus post quem. |
| Egen potentiometer date code | 1960-1964 (year letters documented by the source) | 2 | Dates the pot. Two traps: 'L' is both December and 1964 depending on position, and this Egen year series is NOT the British R=1960 year series used by |
| EIA component source/date codes | whole vintage period | 1 | Component codes date the PART, never the unit. hi-fi-only additions to this layer are the British capacitor codes above and the Fisher house code 1056 |
| Safety warnings that apply to any vintage valve hi-fi | whole vintage period | 4 | Restoration and safety guidance — a warning that comes with reading the part codes, not a dating rule. |
| Japanese electrolytic capacitor date codes - the shared YYWW mechanic | documented samples 1993-2023; no maker states when a format started or ended | 0 | Dates the CAPACITOR, never the unit: it gives a terminus post quem. A recap destroys the evidence, a replaced capacitor is newer than the chassis, and |
| Nippon Chemi-Con date code (year digit + bracketed character) | 2000s production (the repair page was published November 2005) | 2 | One year digit means a whole decade of ambiguity (4 = 1984, 1994 or 2004). The page's own sanity check is that Chemi-Con does not build the same grade |
| Nichicon date code (plant letter + YYWW) | 1990s-2010s (documented 1993 and 2013 samples, same format) | 4 | Some forum answers read the leading letter as a month (e.g. 'B = February'); on the evidence collected here the letter is the plant - with the week al |
| ELNA date code (four digits, YYWW) | 1990s-2000s (documented 2000 and 2003 samples) | 2 | ELNA prints no full part number on many of its caps, so the date code is often the only marking present. Clones exist; the vent shape is the check the |
| Rubycon date code (plant letter + YYWW) | 1990s-2000s (documented 2002 and 2008 samples) | 3 | The same Japanese page records that Rubycon production of the late 1980s to early 1990s was notorious for leaking (fourth-grade-salt electrolyte) - a |
| Matsushita / Panasonic lot-code date (xYMD), SMD parts | 2020s SMD parts (documented example decoded as April 2023) | 1 | A DigiKey community answer, not a Panasonic publication: DigiKey's own staff reply in the same thread says the lot-code meaning is 'specific to the ma |
| Nichicon month letters J-Z (official notice, power capacitors and reactors) | 2004 production numbers; the notice itself is dated 2022-04-01 | 4 | Scope trap: this notice covers high- and low-voltage POWER capacitors and reactors, not miniature aluminium electrolytics. It is encoded because it is |
| Class A heat, bias and the dating trap - safety notes for this wave | whole Class A vintage period (1967-present) | 3 | The valve warnings are NOT duplicated: they still govern every valve ARC unit. |
A21SE — read the number from the outside. Valve equipment of this family stores lethal voltages after it is switched off; the maker's own service text says the chassis should not be opened by anyone without experience.