{
  "format": "circuit-codex-reference",
  "version": 1,
  "id": "aa764",
  "url": "https://circuitcodex.com/amps/aa764/",
  "attribution": "The Analog Maker / Circuit Codex",
  "license": "https://creativecommons.org/licenses/by-sa/4.0/",
  "revision": "ebddc3fd2cf887dca010bbe60487d7391ea6c052",
  "scope": "DC and drawing checks have separate coverage. See included check results and the circuit page; not a dimensioned build template or a physical-build certification.",
  "metadata": {
    "id": "aa764",
    "name_style": "Blackface Champ-style",
    "family": "blackface",
    "era": {
      "start": 1964,
      "end": 1968
    },
    "wattage": 5,
    "tubes": [
      "12AX7",
      "6V6GT",
      "5Y3GT"
    ],
    "topology": {
      "rectifier": {
        "kind": "tube",
        "type": "5Y3GT"
      },
      "bias": "cathode",
      "phase_inverter": "none",
      "tone_stack": "tb"
    },
    "lineage": {
      "derived_from": [
        "5f1"
      ],
      "influenced": []
    },
    "conventions": {
      "designators": "sequential"
    },
    "sources": [
      {
        "desc": "Fender 'Champ Amp AA764' drawing (I-FD), schematic + layout sheets: every component value AND the printed voltage chart read directly from the published sheet — two 68 kΩ input stoppers on a 1 MΩ leak; 12AX7 stages with 100 kΩ plate loads and 1.5 kΩ/25 µF cathodes; treble-bass tone stack (250 pF, 100 kΩ slope, 0.1 µF and 0.047 µF, 250 kΩ treble and bass pots, 15 kΩ to ground) ahead of a 1 MΩ volume; 47 Ω/2.7 kΩ negative-feedback divider under the second cathode; 0.02 µF coupling into a 6V6GT with a 220 kΩ grid leak and a 470 Ω · 1 W cathode; rails +360/+350/+330 on three 20 µF · 450 V cans split by 1 kΩ · 1 W and 10 kΩ · 1 W; 5Y3GT rectifier off a 320-0-320 V winding; transformers TR1 125P1B and TR2 125A35A. Notice: values ±20%, read to ground with an electronic voltmeter. Not reproduced here; archived at EL34World",
        "url": "https://el34world.com/charts/Schematics/files/Fender/Fender_champ_AA764_schem.pdf"
      },
      {
        "desc": "Fender 'Champ-Amp AA764' layout drawing (I-FD), companion sheet to the schematic: the order of the board's parts and every point-to-point lead read from it — the three-node dropper stack over its chassis filter can, the 470 Ω/25 µF and 1.5 kΩ/25 µF cathode networks, the 47 Ω/2.7 kΩ feedback divider, the 220 kΩ/0.02 µF pair at the 6V6 grid, the two 100 kΩ plate loads off one +330 V tie point, the 250 pF/0.047 µF/0.1 µF tone caps beside the 100 kΩ slope resistor, the two 68 kΩ stoppers, and the chassis-mounted 1 MΩ leak at input jack 1 and 15 kΩ leg at the Bass control. Also the wire colours: PT reds and red/yellow, the 5 V yellows, the two greens of the 6.3 V winding (one grounded), the output transformer's blue plate lead with black and yellow secondary, and the brown/blue/white control leads. Not reproduced here; archived at EL34World",
        "url": "https://el34world.com/charts/Schematics/files/Fender/Fender_champ_AA764_layout.pdf"
      }
    ],
    "verification": {
      "status": "verified",
      "date": "2026-08-02T00:00:00.000Z",
      "max_deviation_pct": 19
    },
    "contributors": [
      "TheAnalogMaker"
    ]
  },
  "parts": {
    "notes": "One channel across two input jacks (high/low), each with its own 68 kΩ stopper sharing the 1 MΩ leak. V1B's 1.5 kΩ cathode resistor does not go straight to ground: it lands on a 47 Ω leg that carries the 2.7 kΩ negative-feedback return from the speaker jack, and its 25 µF can bypasses only the 1.5 kΩ. Both transformer part numbers are printed on the drawing, which labels them TR1 (125P1B) and TR2 (125A35A); the output transformer's impedance ratio is not. This list numbers them T1 and T2, the archive's convention where a drawing prints no designators of its own: T1 the power transformer, T2 the output transformer. The 125P1B is the power transformer Fender shared across the Champ, the Princeton and the Princeton Reverb, and the HT winding is not annotated the same way on every sheet: this drawing prints 320-0-320 V, while the Princeton AA964 and Princeton Reverb AA1164 sheets print 340-0-340 V for the same part number. Each entry records the figure its own drawing prints.",
    "items": [
      {
        "ref": "R1",
        "part": "Carbon comp resistor",
        "value": "68 kΩ · ½ W",
        "role": "Input grid stopper, jack 1 (high)"
      },
      {
        "ref": "R2",
        "part": "Carbon comp resistor",
        "value": "68 kΩ · ½ W",
        "role": "Input grid stopper, jack 2 (low)"
      },
      {
        "ref": "R3",
        "part": "Carbon comp resistor",
        "value": "1 MΩ · ½ W",
        "role": "Input grid leak"
      },
      {
        "ref": "R4",
        "part": "Carbon comp resistor",
        "value": "100 kΩ · ½ W",
        "role": "V1A plate load"
      },
      {
        "ref": "R5",
        "part": "Carbon comp resistor",
        "value": "1.5 kΩ · ½ W",
        "role": "V1A cathode bias"
      },
      {
        "ref": "R6",
        "part": "Carbon comp resistor",
        "value": "100 kΩ · ½ W",
        "role": "Tone stack — slope resistor"
      },
      {
        "ref": "R7",
        "part": "Carbon comp resistor",
        "value": "15 kΩ · ½ W",
        "role": "Tone stack — bass leg to ground"
      },
      {
        "ref": "R8",
        "part": "Carbon comp resistor",
        "value": "100 kΩ · ½ W",
        "role": "V1B plate load"
      },
      {
        "ref": "R9",
        "part": "Carbon comp resistor",
        "value": "1.5 kΩ · ½ W",
        "role": "V1B cathode bias"
      },
      {
        "ref": "R10",
        "part": "Carbon comp resistor",
        "value": "47 Ω · ½ W",
        "role": "V1B cathode return / feedback divider leg"
      },
      {
        "ref": "R11",
        "part": "Carbon comp resistor",
        "value": "2.7 kΩ · ½ W",
        "role": "Negative feedback, speaker → V1B cathode divider"
      },
      {
        "ref": "R12",
        "part": "Carbon comp resistor",
        "value": "220 kΩ · ½ W",
        "role": "6V6 grid leak"
      },
      {
        "ref": "R13",
        "part": "Wirewound resistor",
        "value": "470 Ω · 1 W",
        "role": "6V6 cathode bias"
      },
      {
        "ref": "R14",
        "part": "Power resistor",
        "value": "1 kΩ · 1 W",
        "role": "Rail dropper B+1→B+2"
      },
      {
        "ref": "R15",
        "part": "Power resistor",
        "value": "10 kΩ · 1 W",
        "role": "Rail dropper B+2→B+3"
      },
      {
        "ref": "VR1",
        "part": "Audio-taper potentiometer",
        "value": "1 MΩ",
        "role": "Volume"
      },
      {
        "ref": "VR2",
        "part": "Audio-taper potentiometer",
        "value": "250 kΩ",
        "role": "Treble"
      },
      {
        "ref": "VR3",
        "part": "Audio-taper potentiometer",
        "value": "250 kΩ",
        "role": "Bass"
      },
      {
        "ref": "C1",
        "part": "Electrolytic capacitor",
        "value": "25 µF · 25 V",
        "role": "V1A cathode bypass"
      },
      {
        "ref": "C2",
        "part": "Mica capacitor",
        "value": "250 pF",
        "role": "Tone stack — treble cap"
      },
      {
        "ref": "C3",
        "part": "Film capacitor",
        "value": "0.1 µF · 400 V",
        "role": "Tone stack — bass cap"
      },
      {
        "ref": "C4",
        "part": "Film capacitor",
        "value": "0.047 µF · 400 V",
        "role": "Tone stack — bass leg cap"
      },
      {
        "ref": "C5",
        "part": "Electrolytic capacitor",
        "value": "25 µF · 25 V",
        "role": "V1B cathode bypass (across R9 only)"
      },
      {
        "ref": "C6",
        "part": "Coupling capacitor",
        "value": "0.02 µF · 400 V",
        "role": "V1B → 6V6 grid"
      },
      {
        "ref": "C7",
        "part": "Electrolytic capacitor",
        "value": "25 µF · 25 V",
        "role": "6V6 cathode bypass"
      },
      {
        "ref": "C8",
        "part": "Electrolytic capacitor",
        "value": "20 µF · 450 V",
        "role": "Filter, B+1 (reservoir)"
      },
      {
        "ref": "C9",
        "part": "Electrolytic capacitor",
        "value": "20 µF · 450 V",
        "role": "Filter, B+2 (screen)"
      },
      {
        "ref": "C10",
        "part": "Electrolytic capacitor",
        "value": "20 µF · 450 V",
        "role": "Filter, B+3 (preamp)"
      },
      {
        "ref": "C11",
        "part": "Film capacitor",
        "value": "0.047 µF · 600 V",
        "role": "Across the AC line (period part; omitted in modern builds)"
      },
      {
        "ref": "V1",
        "part": "Preamp tube",
        "value": "12AX7",
        "role": "Both gain stages (V1A/V1B)"
      },
      {
        "ref": "V2",
        "part": "Power tube",
        "value": "6V6GT",
        "role": "Single-ended output"
      },
      {
        "ref": "V3",
        "part": "Rectifier tube",
        "value": "5Y3GT",
        "role": "Full-wave rectifier (V3A/V3B)"
      },
      {
        "ref": "T1",
        "part": "Power transformer",
        "value": "Fender 125P1B · 320-0-320 V · 6.3 V · 5 V",
        "role": "HT + heaters + rectifier filament"
      },
      {
        "ref": "T2",
        "part": "Output transformer",
        "value": "Fender 125A35A",
        "role": "Single-ended output (impedance ratio not marked on the drawing)"
      },
      {
        "ref": "—",
        "part": "Fuse",
        "value": "1 A slo-blo",
        "role": "Mains fuse"
      }
    ]
  },
  "publishedVoltages": {
    "source": "Fender 'Champ Amp AA764' drawing (I-FD), printed chart: +360 V (reservoir / OT primary feed), +350 V (6V6 plate pin 3 and screen pin 4), +330 V (preamp rail), +19 V (6V6 cathode pin 8), +200 V / +1.8 V (12AX7 first stage plate and cathode), +205 V / +1.7 V (12AX7 second stage plate and cathode)",
    "nodes": {
      "BP2": {
        "chart": 350,
        "tol_pct": 5,
        "note": "6V6 screen node, after the 1 kΩ · 1 W dropper (R14)"
      },
      "BP3": {
        "chart": 330,
        "tol_pct": 5,
        "note": "preamp plate rail, after the 10 kΩ · 1 W dropper (R15)"
      },
      "P1A": {
        "chart": 200,
        "tol_pct": 20,
        "note": "12AX7 first-stage plate, chart pin 1"
      },
      "K1A": {
        "chart": 1.8,
        "tol_pct": 20,
        "note": "12AX7 first-stage cathode over 1.5 kΩ, chart pin 3. Read +1.8; the I-FD layout page settles it (V1 audit 2026-10-03, aa764.md): its glyph (2171x1591, crop 1540,980,1640,1070) closes its lower bowl, unlike the 9 of the same page's +19V (crop 1020,990,1090,1060). The 72 ppi I-FD schematic is too coarse to decide; it does not contradict the layout. Until then the corpus carried +1.9"
      },
      "P1B": {
        "chart": 205,
        "tol_pct": 20,
        "note": "12AX7 second-stage plate, chart pin 6"
      },
      "K1B": {
        "chart": 1.7,
        "tol_pct": 20,
        "note": "12AX7 second-stage cathode, chart pin 8 — 1.5 kΩ down to the 47 Ω/2.7 kΩ feedback divider"
      },
      "K2": {
        "chart": 19,
        "tol_pct": 20,
        "note": "6V6GT cathode over 470 Ω · 1 W, chart pin 8"
      }
    }
  },
  "operatingPoint": [
    {
      "node": "BP2",
      "chart": 350,
      "sim": 354.031,
      "disputed": false,
      "dev_pct": 1.1517142857142872,
      "tol_pct": 5,
      "gated": true,
      "within": true,
      "note": "6V6 screen node, after the 1 kΩ · 1 W dropper (R14)",
      "dispute_note": ""
    },
    {
      "node": "BP3",
      "chart": 330,
      "sim": 331.518,
      "disputed": false,
      "dev_pct": 0.4599999999999916,
      "tol_pct": 5,
      "gated": true,
      "within": true,
      "note": "preamp plate rail, after the 10 kΩ · 1 W dropper (R15)",
      "dispute_note": ""
    },
    {
      "node": "P1A",
      "chart": 200,
      "sim": 218.134,
      "disputed": false,
      "dev_pct": 9.066999999999993,
      "tol_pct": 20,
      "gated": true,
      "within": true,
      "note": "12AX7 first-stage plate, chart pin 1",
      "dispute_note": ""
    },
    {
      "node": "K1A",
      "chart": 1.8,
      "sim": 1.701,
      "disputed": false,
      "dev_pct": 5.499999999999998,
      "tol_pct": 20,
      "gated": true,
      "within": true,
      "note": "12AX7 first-stage cathode over 1.5 kΩ, chart pin 3. Read +1.8; the I-FD layout page settles it (V1 audit 2026-10-03, aa764.md): its glyph (2171x1591, crop 1540,980,1640,1070) closes its lower bowl, unlike the 9 of the same page's +19V (crop 1020,990,1090,1060). The 72 ppi I-FD schematic is too coarse to decide; it does not contradict the layout. Until then the corpus carried +1.9",
      "dispute_note": ""
    },
    {
      "node": "P1B",
      "chart": 205,
      "sim": 219.771,
      "disputed": false,
      "dev_pct": 7.205365853658529,
      "tol_pct": 20,
      "gated": true,
      "within": true,
      "note": "12AX7 second-stage plate, chart pin 6",
      "dispute_note": ""
    },
    {
      "node": "K1B",
      "chart": 1.7,
      "sim": 1.728,
      "disputed": false,
      "dev_pct": 1.6470588235294132,
      "tol_pct": 20,
      "gated": true,
      "within": true,
      "note": "12AX7 second-stage cathode, chart pin 8 — 1.5 kΩ down to the 47 Ω/2.7 kΩ feedback divider",
      "dispute_note": ""
    },
    {
      "node": "K2",
      "chart": 19,
      "sim": 22.602,
      "disputed": false,
      "dev_pct": 18.957894736842107,
      "tol_pct": 20,
      "gated": true,
      "within": true,
      "note": "6V6GT cathode over 470 Ω · 1 W, chart pin 8",
      "dispute_note": ""
    }
  ],
  "checks": [
    {
      "id": "dc",
      "title": "DC operating point",
      "status": "Verified",
      "summary": "7 reference nodes are within tolerance. Maintainer verification is recorded for 2026-08-02; changes since then are awaiting maintainer re-review.",
      "details": [
        "The circuit's facts (netlist, reference voltages, parts list, both drawings' connections, capacitor polarity marks and heater declarations) have changed since the maintainer's review, or no review fingerprint is on record yet. The badge stands on its date until the maintainer re-reviews.",
        "This compares simulated DC conditions with the cited reference. It does not test sound, physical construction or every part of the circuit."
      ],
      "tone": "checked"
    },
    {
      "id": "schematic",
      "title": "Schematic against DC model",
      "status": "Checked",
      "summary": "Connectivity of modelled components is checked on every change.",
      "details": [
        "Parts outside the DC model need separate checks and source review."
      ],
      "tone": "checked"
    },
    {
      "id": "board",
      "title": "Board against DC model",
      "status": "Checked",
      "summary": "Connectivity of modelled components is checked on every change.",
      "details": [
        "This does not establish heater wiring or physical spacing."
      ],
      "tone": "checked"
    },
    {
      "id": "drawings",
      "title": "Schematic against board",
      "status": "No open findings",
      "summary": "No disagreement is listed in the published comparison.",
      "details": [
        "A finding identifies a difference or a coverage gap. The factory source must decide which drawing, if either, needs correction.",
        "1 sheet-only part is explicitly excluded: C11. Heaters and the pilot lamp are checked separately."
      ],
      "tone": "checked"
    },
    {
      "id": "heaters",
      "title": "Heater and filament wiring",
      "status": "Not established",
      "summary": "The drawn supply-leg connections have not been established by this check.",
      "details": [
        "Supply-leg grouping still needs confirmation at V1.",
        "The I-FD layout sheet exists, but every located copy is the same 2171 x 1591 (200 ppi) JPEG — the el34world PDF and each of its Internet Archive captures from 2016 to 2025 — and it does not resolve the socket pins; the Vibro-Champ page of the same drawing family was read at 708 ppi and declared, and a copy of this sheet at that class of resolution is what clears these sockets.",
        "V1: pins [4, 5] are one leg at 6.3 V and opposite legs at 12.6 V"
      ],
      "tone": "attention"
    },
    {
      "id": "polarity",
      "title": "Capacitor polarity",
      "status": "Partial",
      "summary": "1 capacitor marking cannot be confirmed by the DC model.",
      "details": [
        "C5: C5.a: on KFB, which has no simulated volts"
      ],
      "tone": "attention"
    }
  ],
  "corrections": [
    {
      "id": "aa764-k1a-2026-10-03",
      "date": "2026-10-03",
      "amps": [
        "aa764"
      ],
      "title": "AA764 first-stage cathode voltage",
      "description": "The first-stage cathode figure is +1.8 V, as the factory layout page prints it; we had +1.9 V. The low-resolution schematic is too coarse to decide the digit, and the notes now say so. The simulated value remains within tolerance.",
      "commit": "70b4558d1263ed8d7ed812710d1fb8fa50d489cd",
      "url": "https://github.com/TheAnalogMaker/circuit-codex/commit/70b4558d1263ed8d7ed812710d1fb8fa50d489cd"
    }
  ],
  "sourceDirectory": "https://github.com/TheAnalogMaker/circuit-codex/tree/ebddc3fd2cf887dca010bbe60487d7391ea6c052/amps/aa764"
}