{
  "format": "circuit-codex-reference",
  "version": 1,
  "id": "aa864-bassman",
  "url": "https://circuitcodex.com/amps/aa864-bassman/",
  "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": "aa864-bassman",
    "name_style": "Blackface Bassman-style",
    "family": "blackface",
    "era": {
      "start": 1964,
      "end": 1965
    },
    "wattage": 50,
    "tubes": [
      7025,
      7025,
      7025,
      "12AT7",
      "6L6GC",
      "6L6GC"
    ],
    "topology": {
      "rectifier": {
        "kind": "solid-state",
        "type": "silicon, 3 diodes per phase"
      },
      "bias": "fixed",
      "phase_inverter": "long-tailed-pair",
      "tone_stack": "tb"
    },
    "lineage": {
      "derived_from": [
        "6g6b"
      ],
      "influenced": [
        "ab165"
      ]
    },
    "conventions": {
      "designators": "functional"
    },
    "sources": [
      {
        "desc": "Fender 'BASSMAN-AMP AA864' drawing, title block read directly: FENDER MODEL \"BASSMAN-AMP AA864\" P/B, drawing code H-FD, Fender Electric Instrument Co., Fullerton, California. Every component value and the whole printed voltage chart read from that sheet — two channels (Bass Instrument, Normal) on three 7025 bottles, a 12AT7 long-tailed-pair phase inverter, a fixed-bias 6L6GC (2) pair, and solid-state rectification (three series silicon diodes per phase). Printed chart: +422 (reservoir, and again at the OT centre tap / choke input past the standby switch), +420 (6L6 plates), +420 (screen rail after the choke, and again at the 6L6 screens), +410 (PI plate rail), +340 (preamp rail — the layout sheet marks the same node +380; see the operating-point table), +250/+250 (Normal channel plates), +235/+235 (Bass channel plates), +240 (Bass-channel driver plate), +220/+205 (PI plates), +95 (PI cathodes), +93 (PI tail junction), +2.0/+2.0/+1.8/+1.8/+1.9 (preamp cathodes), −44 (fixed bias). Notice on the sheet: \"Voltages read to ground with electronic voltmeter. Values shown + or − 20%. All resistors 1/2 watt, 10% tolerance if not specified. All capacitors at least 400 volt rating if not specified.\" Transformer table on the sheet: TR1 125P7D (125P7DX on the export model), TR2 125C1A choke, TR3 125A13A output. Not reproduced here; archived at EL34World",
        "url": "https://el34world.com/charts/Schematics/files/Fender/Fender_bassman_aa864.pdf"
      },
      {
        "desc": "Fender 'BASSMAN-AMP AA864' layout drawing, title block read directly: FENDER MODEL \"BASSMAN-AMP AA864\" LAYOUT P/B, drawing code H-FD, Fender Electric Instrument Company, Fullerton, California, U.S.A. — the same two notices as the circuit sheet. The order in which the board carries its parts, the chassis positions of the six sockets (6L6GC · 6L6GC · 12AT7 · 7025 · 7025 · 7025), the two control clusters and their part numbers, and the wire colours of the transformer leads are read from it. It also prints +380 V at the preamp-rail eyelet, where the circuit sheet prints +340 V. Not reproduced here; archived at EL34World",
        "url": "https://el34world.com/charts/Schematics/Files/Fender/Fender_bassman_aa864_layout.pdf"
      },
      {
        "desc": "Wikipedia, 'Fender Bassman' — the AA864 dated 1964 as the first blackface Bassman, a 50-watt piggyback head over a separate cabinet, superseded by the AB165 c. 1965. The drawing prints no power rating, so the 50 W figure is carried from here and from this corpus's own Bassman family file, not read off the sheet",
        "url": "https://en.wikipedia.org/wiki/Fender_Bassman"
      }
    ],
    "verification": {
      "status": "verified",
      "date": "2026-08-13T00:00:00.000Z",
      "max_deviation_pct": 11.6
    },
    "added": "2026-08-08T00:00:00.000Z",
    "contributors": [
      "TheAnalogMaker"
    ],
    "sections": {
      "V3A": "unused — the H-FD layout page wires V3 pins 6, 7 and 8 only; pins 1, 2 and 3 are bare, and the schematic draws only V3B, the bass channel's third stage"
    }
  },
  "parts": {
    "notes": "Both pages draw two input jacks per channel, each with its own 68 kΩ stopper, and hang the channel's 1 MΩ leak from jack 1's tip, jack side of its stopper; the mains fuse and the AC switch sit on opposite legs of the line. Three 7025 bottles supply six triode sections and the circuit uses five — the Bass channel takes three stages and the Normal channel two — so one section is unused; the sheet does not say which bottle carries it. The tone stacks differ between channels: the Normal channel draws the blackface two-knob ladder (100 kΩ slope + 250 pF off the plate, 0.1 µF to the treble-lug/bass node, bass rheostat over the 0.047 µF / 6.8 kΩ foot), while the Bass channel draws the same ladder with a 220 kΩ resistor above a 50 kΩ treble pot, a 10 kΩ bass pot, three 0.1 µF caps off the slope node instead of the Normal channel's 0.1 / 0.047 pair, and a Deep switch that parallels the third of them into the grounded foot.",
    "items": [
      {
        "ref": "R1b",
        "part": "Carbon comp resistor",
        "value": "68 kΩ · ½ W",
        "role": "Bass input grid stopper (jack 1)"
      },
      {
        "ref": "R2b",
        "part": "Carbon comp resistor",
        "value": "68 kΩ · ½ W",
        "role": "Bass input grid stopper (jack 2)"
      },
      {
        "ref": "RGB1",
        "part": "Carbon comp resistor",
        "value": "1 MΩ · ½ W",
        "role": "Bass input leak, jack 1's tip to ground (the V1a grid returns through R1b)"
      },
      {
        "ref": "RLB1",
        "part": "Carbon comp resistor",
        "value": "100 kΩ · ½ W",
        "role": "V1a plate load"
      },
      {
        "ref": "RKB1",
        "part": "Carbon comp resistor",
        "value": "1.5 kΩ · ½ W",
        "role": "V1a cathode bias"
      },
      {
        "ref": "CKB1",
        "part": "Electrolytic capacitor",
        "value": "25 µF · 25 V",
        "role": "V1a cathode bypass"
      },
      {
        "ref": "CTB",
        "part": "Mica capacitor",
        "value": "250 pF",
        "role": "Bass-channel treble cap, off the V1a plate"
      },
      {
        "ref": "RTB",
        "part": "Carbon comp resistor",
        "value": "220 kΩ · ½ W",
        "role": "Bass-channel treble series resistor, above the treble pot"
      },
      {
        "ref": "VRTB",
        "part": "Potentiometer",
        "value": "50 kΩ-A",
        "role": "Bass-channel treble"
      },
      {
        "ref": "RSB1",
        "part": "Carbon comp resistor",
        "value": "100 kΩ · ½ W",
        "role": "Bass-channel slope resistor, plate to the ladder node"
      },
      {
        "ref": "CBB1",
        "part": "Coupling capacitor",
        "value": "0.1 µF",
        "role": "Bass-channel ladder cap, slope node to the treble-lug/bass-top junction"
      },
      {
        "ref": "CBB2",
        "part": "Coupling capacitor",
        "value": "0.1 µF",
        "role": "Bass-channel ladder cap, slope node to the bass-pot foot"
      },
      {
        "ref": "CBB3",
        "part": "Coupling capacitor",
        "value": "0.1 µF",
        "role": "Bass-channel Deep cap, switched in parallel with CBB2"
      },
      {
        "ref": "SWDEEP",
        "part": "Toggle switch",
        "value": "SPST",
        "role": "Deep switch — parallels CBB3 into the ladder foot"
      },
      {
        "ref": "VRBB",
        "part": "Potentiometer",
        "value": "10 kΩ-A",
        "role": "Bass-channel bass (rheostat in the ladder)"
      },
      {
        "ref": "VRVB",
        "part": "Audio-taper potentiometer",
        "value": "250 kΩ-A",
        "role": "Bass-channel volume"
      },
      {
        "ref": "RLB2",
        "part": "Carbon comp resistor",
        "value": "100 kΩ · ½ W",
        "role": "V1b plate load"
      },
      {
        "ref": "RKB2",
        "part": "Carbon comp resistor",
        "value": "1.5 kΩ · ½ W",
        "role": "V1b cathode bias"
      },
      {
        "ref": "CKB2",
        "part": "Electrolytic capacitor",
        "value": "25 µF · 25 V",
        "role": "V1b cathode bypass"
      },
      {
        "ref": "CCB2",
        "part": "Coupling capacitor",
        "value": "0.1 µF",
        "role": "V1b plate → driver grid divider"
      },
      {
        "ref": "RDV1",
        "part": "Carbon comp resistor",
        "value": "220 kΩ · ½ W",
        "role": "Driver grid divider, series leg"
      },
      {
        "ref": "RDV2",
        "part": "Carbon comp resistor",
        "value": "220 kΩ · ½ W",
        "role": "Driver grid divider, shunt leg"
      },
      {
        "ref": "CDV",
        "part": "Mica capacitor",
        "value": "0.001 µF",
        "role": "Driver grid divider shunt cap, across RDV2"
      },
      {
        "ref": "RLB3",
        "part": "Carbon comp resistor",
        "value": "100 kΩ · ½ W",
        "role": "Driver plate load"
      },
      {
        "ref": "CLB3",
        "part": "Mica capacitor",
        "value": "0.003 µF",
        "role": "Driver plate-load bypass — treble roll-off across RLB3 (lettered '.003' on the layout; the schematic's last digit is ink-filled)"
      },
      {
        "ref": "RKB3",
        "part": "Carbon comp resistor",
        "value": "1.5 kΩ · ½ W",
        "role": "Driver cathode bias (no bypass capacitor)"
      },
      {
        "ref": "RMXB",
        "part": "Carbon comp resistor",
        "value": "220 kΩ · ½ W",
        "role": "Bass-channel mix resistor into the phase-inverter grid node"
      },
      {
        "ref": "R1n",
        "part": "Carbon comp resistor",
        "value": "68 kΩ · ½ W",
        "role": "Normal input grid stopper (jack 1)"
      },
      {
        "ref": "R2n",
        "part": "Carbon comp resistor",
        "value": "68 kΩ · ½ W",
        "role": "Normal input grid stopper (jack 2)"
      },
      {
        "ref": "RGN1",
        "part": "Carbon comp resistor",
        "value": "1 MΩ · ½ W",
        "role": "Normal input leak, jack 1's tip to ground (the V2a grid returns through R1n)"
      },
      {
        "ref": "RLN1",
        "part": "Carbon comp resistor",
        "value": "100 kΩ · ½ W",
        "role": "V2a plate load"
      },
      {
        "ref": "RKN1",
        "part": "Carbon comp resistor",
        "value": "1.5 kΩ · ½ W",
        "role": "V2a cathode bias"
      },
      {
        "ref": "CKN1",
        "part": "Electrolytic capacitor",
        "value": "25 µF · 25 V",
        "role": "V2a cathode bypass"
      },
      {
        "ref": "CTN",
        "part": "Mica capacitor",
        "value": "250 pF",
        "role": "Normal treble cap, off the V2a plate"
      },
      {
        "ref": "VRTN",
        "part": "Potentiometer",
        "value": "250 kΩ-A",
        "role": "Normal treble"
      },
      {
        "ref": "RSN",
        "part": "Carbon comp resistor",
        "value": "100 kΩ · ½ W",
        "role": "Normal tone-stack slope resistor"
      },
      {
        "ref": "CBN",
        "part": "Coupling capacitor",
        "value": "0.1 µF",
        "role": "Normal tone-stack bass cap, slope node to the bass pot"
      },
      {
        "ref": "VRBN",
        "part": "Potentiometer",
        "value": "250 kΩ-A",
        "role": "Normal bass (rheostat in the ladder)"
      },
      {
        "ref": "CBN2",
        "part": "Coupling capacitor",
        "value": "0.047 µF",
        "role": "Normal tone-stack middle-leg cap, slope node to the bleed resistor"
      },
      {
        "ref": "RSLN",
        "part": "Carbon comp resistor",
        "value": "6.8 kΩ · ½ W",
        "role": "Normal tone-stack bleed resistor"
      },
      {
        "ref": "VRVN",
        "part": "Audio-taper potentiometer",
        "value": "1 MΩ-A",
        "role": "Normal volume"
      },
      {
        "ref": "CBRN",
        "part": "Mica capacitor",
        "value": "120 pF",
        "role": "Normal bright cap, across the volume pot (top lug to wiper)"
      },
      {
        "ref": "SWBRT",
        "part": "Toggle switch",
        "value": "SPST",
        "role": "Bright switch — puts CBRN across the volume pot"
      },
      {
        "ref": "RLN2",
        "part": "Carbon comp resistor",
        "value": "100 kΩ · ½ W",
        "role": "V2b plate load"
      },
      {
        "ref": "RKN2",
        "part": "Carbon comp resistor",
        "value": "1.5 kΩ · ½ W",
        "role": "V2b cathode bias"
      },
      {
        "ref": "CKN2",
        "part": "Electrolytic capacitor",
        "value": "25 µF · 25 V",
        "role": "V2b cathode bypass"
      },
      {
        "ref": "RMXN",
        "part": "Carbon comp resistor",
        "value": "220 kΩ · ½ W",
        "role": "Normal-channel mix resistor into the phase-inverter grid node"
      },
      {
        "ref": "CPI",
        "part": "Mica capacitor",
        "value": "500 pF",
        "role": "Mix node → PI hot-grid coupling"
      },
      {
        "ref": "RLPA",
        "part": "Carbon comp resistor",
        "value": "82 kΩ · ½ W · 5%",
        "role": "PI plate load (hot side)"
      },
      {
        "ref": "RLPB",
        "part": "Carbon comp resistor",
        "value": "100 kΩ · ½ W · 5%",
        "role": "PI plate load (cold side)"
      },
      {
        "ref": "RGPA",
        "part": "Carbon comp resistor",
        "value": "1 MΩ · ½ W",
        "role": "PI grid leak (hot), returned to the tail junction"
      },
      {
        "ref": "RGPB",
        "part": "Carbon comp resistor",
        "value": "1 MΩ · ½ W",
        "role": "PI grid leak (cold), returned to the tail junction"
      },
      {
        "ref": "RTAIL",
        "part": "Carbon comp resistor",
        "value": "470 Ω · ½ W",
        "role": "PI cathode resistor"
      },
      {
        "ref": "RT2",
        "part": "Carbon comp resistor",
        "value": "22 kΩ · ½ W",
        "role": "PI tail (junction → feedback node)"
      },
      {
        "ref": "RNF",
        "part": "Carbon comp resistor",
        "value": "100 Ω · ½ W",
        "role": "Feedback node → ground; the tail's return and the NFB divider foot"
      },
      {
        "ref": "RNFB",
        "part": "Carbon comp resistor",
        "value": "820 Ω · ½ W",
        "role": "Negative feedback, OT secondary → feedback node (DC-neutral)"
      },
      {
        "ref": "CPIB",
        "part": "Coupling capacitor",
        "value": "0.1 µF · 200 V",
        "role": "Feedback node → PI cold grid"
      },
      {
        "ref": "C1",
        "part": "Coupling capacitor",
        "value": "0.1 µF · 400 V",
        "role": "PI hot plate → V5 grid"
      },
      {
        "ref": "C2",
        "part": "Coupling capacitor",
        "value": "0.1 µF · 400 V",
        "role": "PI cold plate → V6 grid"
      },
      {
        "ref": "RGL1",
        "part": "Carbon comp resistor",
        "value": "220 kΩ · ½ W · 5%",
        "role": "V5 grid leak, from the −44 V bias line"
      },
      {
        "ref": "RGL2",
        "part": "Carbon comp resistor",
        "value": "220 kΩ · ½ W · 5%",
        "role": "V6 grid leak, from the −44 V bias line"
      },
      {
        "ref": "RGS1",
        "part": "Carbon comp resistor",
        "value": "1.5 kΩ · ½ W",
        "role": "V5 grid stopper"
      },
      {
        "ref": "RGS2",
        "part": "Carbon comp resistor",
        "value": "1.5 kΩ · ½ W",
        "role": "V6 grid stopper"
      },
      {
        "ref": "RS1",
        "part": "Wirewound resistor",
        "value": "470 Ω · 1 W",
        "role": "V5 screen resistor"
      },
      {
        "ref": "RS2",
        "part": "Wirewound resistor",
        "value": "470 Ω · 1 W",
        "role": "V6 screen resistor"
      },
      {
        "ref": "T3",
        "part": "Output transformer",
        "value": "Fender 125A13A",
        "role": "Push-pull 6L6GC output, into the 2x12 cabinet + EXT SPKR jack"
      },
      {
        "ref": "T1",
        "part": "Power transformer",
        "value": "Fender 125P7D · 305-0-305 V AC",
        "role": "HT + heaters + pilot (export model: 125P7DX)"
      },
      {
        "ref": "T2",
        "part": "Filter choke",
        "value": "Fender 125C1A",
        "role": "Plate rail → screen rail"
      },
      {
        "ref": "D1",
        "part": "Rectifier diode",
        "value": "silicon",
        "role": "HT rectifier, upper phase (1 of 3 in series)"
      },
      {
        "ref": "D2",
        "part": "Rectifier diode",
        "value": "silicon",
        "role": "HT rectifier, upper phase (2 of 3 in series)"
      },
      {
        "ref": "D3",
        "part": "Rectifier diode",
        "value": "silicon",
        "role": "HT rectifier, upper phase (3 of 3 in series)"
      },
      {
        "ref": "D4",
        "part": "Rectifier diode",
        "value": "silicon",
        "role": "HT rectifier, lower phase (1 of 3 in series)"
      },
      {
        "ref": "D5",
        "part": "Rectifier diode",
        "value": "silicon",
        "role": "HT rectifier, lower phase (2 of 3 in series)"
      },
      {
        "ref": "D6",
        "part": "Rectifier diode",
        "value": "silicon",
        "role": "HT rectifier, lower phase (3 of 3 in series)"
      },
      {
        "ref": "C10",
        "part": "Electrolytic capacitor",
        "value": "70 µF · 350 V",
        "role": "Reservoir, upper half of the series pair (+422 V node)"
      },
      {
        "ref": "C11",
        "part": "Electrolytic capacitor",
        "value": "70 µF · 350 V",
        "role": "Reservoir, lower half of the series pair"
      },
      {
        "ref": "RBL1",
        "part": "Wirewound resistor",
        "value": "220 kΩ · 1 W",
        "role": "Reservoir balancing resistor, across C10"
      },
      {
        "ref": "RBL2",
        "part": "Wirewound resistor",
        "value": "220 kΩ · 1 W",
        "role": "Reservoir balancing resistor, across C11"
      },
      {
        "ref": "SWSTBY",
        "part": "Toggle switch",
        "value": "SPST",
        "role": "Standby — +422 V reservoir to the plate rail / choke input"
      },
      {
        "ref": "C12",
        "part": "Electrolytic capacitor",
        "value": "20 µF · 525 V",
        "role": "Filter, screen rail (+420 V, past the choke)"
      },
      {
        "ref": "RD1",
        "part": "Wirewound resistor",
        "value": "1 kΩ · 1 W",
        "role": "Rail dropper, screens → phase-inverter rail"
      },
      {
        "ref": "C13",
        "part": "Electrolytic capacitor",
        "value": "20 µF · 525 V",
        "role": "Filter, phase-inverter rail (+410 V)"
      },
      {
        "ref": "RD2",
        "part": "Wirewound resistor",
        "value": "4.7 kΩ · 1 W",
        "role": "Rail dropper, phase-inverter rail → preamp rail"
      },
      {
        "ref": "C14",
        "part": "Electrolytic capacitor",
        "value": "20 µF · 525 V",
        "role": "Filter, preamp rail (+380 V on the layout sheet — see the operating-point table)"
      },
      {
        "ref": "RBIAS",
        "part": "Wirewound resistor",
        "value": "470 Ω · 1 W",
        "role": "Bias-supply series resistor, off the 305 V AC tap"
      },
      {
        "ref": "DBIAS",
        "part": "Rectifier diode",
        "value": "silicon",
        "role": "Bias-supply rectifier"
      },
      {
        "ref": "CB1",
        "part": "Electrolytic capacitor",
        "value": "25 µF · 50 V",
        "role": "Bias-supply filter"
      },
      {
        "ref": "VRBIAS",
        "part": "Linear potentiometer",
        "value": "10 kΩ-L",
        "role": "Bias adjust — wiper feeds the 220 kΩ grid leaks"
      },
      {
        "ref": "RBIAS2",
        "part": "Carbon comp resistor",
        "value": "15 kΩ · ½ W",
        "role": "Bias divider, pot to ground"
      },
      {
        "ref": "FUSE",
        "part": "Fuse",
        "value": "2 A slo-blo",
        "role": "Mains fuse, on the line leg opposite the AC switch"
      },
      {
        "ref": "SWAC",
        "part": "Toggle switch",
        "value": "SPST",
        "role": "AC switch"
      },
      {
        "ref": "SWGND",
        "part": "Toggle switch",
        "value": "SPDT",
        "role": "Ground switch (period; not in modern builds)"
      },
      {
        "ref": "CDEATH",
        "part": "Ceramic capacitor",
        "value": "0.047 µF · 600 V",
        "role": "Ground-switch cap (period; not in modern builds)"
      },
      {
        "ref": "V1",
        "part": "Preamp tube",
        "value": "7025",
        "role": "Bass channel input + 2nd stage (V1a/V1b)"
      },
      {
        "ref": "V2",
        "part": "Preamp tube",
        "value": "7025",
        "role": "Normal channel input + 2nd stage (V2a/V2b)"
      },
      {
        "ref": "V3",
        "part": "Preamp tube",
        "value": "7025",
        "role": "Bass channel driver (V3b); one triode section is unused"
      },
      {
        "ref": "V4",
        "part": "Preamp/driver tube",
        "value": "12AT7",
        "role": "Long-tailed-pair phase inverter"
      },
      {
        "ref": "V5",
        "part": "Power tube",
        "value": "6L6GC",
        "role": "Push-pull output (hot side)"
      },
      {
        "ref": "V6",
        "part": "Power tube",
        "value": "6L6GC",
        "role": "Push-pull output (cold side)"
      }
    ]
  },
  "publishedVoltages": {
    "source": "Fender AA864 Bassman-Amp drawing, printed voltages: +422 (reservoir, and again at the OT centre tap / choke input past the standby switch), +420 (6L6GC plates), +420 (screen rail past the TR2 choke, and again at the 6L6GC screens), +410 (phase-inverter plate rail), +380 (preamp rail, from the layout sheet; the circuit sheet prints +340 at the same node — see the BPR note), +250 (Normal channel plates, both stages), +235 (Bass channel plates, both stages), +240 (Bass-channel driver plate), +220/+205 (PI plates, 82k/100k sides), +95 (PI joined cathodes), +93 (PI tail junction), +2.0 (Bass channel cathodes), +1.8 (Normal channel cathodes), +1.9 (driver cathode), -44 (6L6GC fixed bias)",
    "nodes": {
      "S61": {
        "chart": 420,
        "tol_pct": 8,
        "note": "6L6GC (V5) screen after its 470 Ohm-1W stopper, off the +420 screen rail"
      },
      "G61": {
        "chart": -44,
        "tol_pct": 8,
        "note": "6L6GC (V5) grid, fixed bias via 220k from the -44 V supply, through the 1.5k stopper"
      },
      "BPI": {
        "chart": 410,
        "tol_pct": 5,
        "note": "phase-inverter plate rail, derived from the driven +420 screen rail through the drawn 1 kOhm-1W dropper"
      },
      "BPR": {
        "chart": 380,
        "tol_pct": 20,
        "note": "Preamp rail, below the 4.7 kOhm-1W dropper. The two published sheets print two different figures at this node and only one of them closes. The LAYOUT sheet marks the eyelet that feeds the preamp plate loads +380 V; the circuit sheet marks the same node +340 V. Take the circuit sheet's figure and the drawn resistor must pass (410-340)/4.7k = 14.9 mA, but the only load is five 100 kOhm-loaded preamp triodes. Take the layout sheet's and the arithmetic closes: (380-235)/100k + (380-235)/100k + (380-250)/100k + (380-250)/100k + (380-240)/100k = 6.90 mA, a 32 V drop, putting the node at +378 V. The entry therefore carries the layout sheet's +380 V and records the circuit sheet's +340 V as the figure that does not close."
      },
      "PB1": {
        "chart": 235,
        "tol_pct": 20,
        "note": "Bass channel input plate (V1a), 100k from the preamp rail"
      },
      "KB1": {
        "chart": 2,
        "tol_pct": 20,
        "note": "Bass channel input cathode over 1.5k (25 uF bypass)"
      },
      "PB2": {
        "chart": 235,
        "tol_pct": 20,
        "note": "Bass channel 2nd-stage plate (V1b), 100k from the preamp rail"
      },
      "KB2": {
        "chart": 2,
        "tol_pct": 20,
        "note": "Bass channel 2nd-stage cathode over 1.5k (25 uF bypass)"
      },
      "PB3": {
        "chart": 240,
        "tol_pct": 20,
        "note": "Bass channel driver plate (V3b), 100k with 0.003 uF across it"
      },
      "KB3": {
        "chart": 1.9,
        "tol_pct": 20,
        "note": "Bass channel driver cathode over 1.5k — the one preamp cathode with no bypass can"
      },
      "PN1": {
        "chart": 250,
        "tol_pct": 20,
        "note": "Normal channel input plate (V2a), 100k from the preamp rail"
      },
      "KN1": {
        "chart": 1.8,
        "tol_pct": 20,
        "note": "Normal channel input cathode over 1.5k (25 uF bypass)"
      },
      "PN2": {
        "chart": 250,
        "tol_pct": 20,
        "note": "Normal channel 2nd-stage plate (V2b), 100k from the preamp rail"
      },
      "KN2": {
        "chart": 1.8,
        "tol_pct": 20,
        "note": "Normal channel 2nd-stage cathode over 1.5k (25 uF bypass)"
      },
      "PPA": {
        "chart": 220,
        "tol_pct": 20,
        "note": "PI plate, 82k (hot) side"
      },
      "PPB": {
        "chart": 205,
        "tol_pct": 20,
        "note": "PI plate, 100k (cold) side"
      },
      "KPI": {
        "chart": 95,
        "tol_pct": 20,
        "note": "PI joined cathodes, above the 470 Ohm"
      },
      "JPI": {
        "chart": 93,
        "tol_pct": 20,
        "note": "PI tail junction (470 Ohm / 22k), grid-leak return"
      },
      "NFB": {
        "chart": null,
        "note": "negative-feedback node — the 22k tail's return, working into the 100 Ohm to ground. Not printed on the chart; reported for information"
      }
    }
  },
  "operatingPoint": [
    {
      "node": "S61",
      "chart": 420,
      "sim": 419.201,
      "disputed": false,
      "dev_pct": 0.19023809523809004,
      "tol_pct": 8,
      "gated": true,
      "within": true,
      "note": "6L6GC (V5) screen after its 470 Ohm-1W stopper, off the +420 screen rail",
      "dispute_note": ""
    },
    {
      "node": "G61",
      "chart": -44,
      "sim": -44,
      "disputed": false,
      "dev_pct": 0,
      "tol_pct": 8,
      "gated": true,
      "within": true,
      "note": "6L6GC (V5) grid, fixed bias via 220k from the -44 V supply, through the 1.5k stopper",
      "dispute_note": ""
    },
    {
      "node": "BPI",
      "chart": 410,
      "sim": 409.62,
      "disputed": false,
      "dev_pct": 0.09268292682926718,
      "tol_pct": 5,
      "gated": true,
      "within": true,
      "note": "phase-inverter plate rail, derived from the driven +420 screen rail through the drawn 1 kOhm-1W dropper",
      "dispute_note": ""
    },
    {
      "node": "BPR",
      "chart": 380,
      "sim": 379.353,
      "disputed": false,
      "dev_pct": 0.17026315789473456,
      "tol_pct": 20,
      "gated": true,
      "within": true,
      "note": "Preamp rail, below the 4.7 kOhm-1W dropper. The two published sheets print two different figures at this node and only one of them closes. The LAYOUT sheet marks the eyelet that feeds the preamp plate loads +380 V; the circuit sheet marks the same node +340 V. Take the circuit sheet's figure and the drawn resistor must pass (410-340)/4.7k = 14.9 mA, but the only load is five 100 kOhm-loaded preamp triodes. Take the layout sheet's and the arithmetic closes: (380-235)/100k + (380-235)/100k + (380-250)/100k + (380-250)/100k + (380-240)/100k = 6.90 mA, a 32 V drop, putting the node at +378 V. The entry therefore carries the layout sheet's +380 V and records the circuit sheet's +340 V as the figure that does not close.",
      "dispute_note": ""
    },
    {
      "node": "PB1",
      "chart": 235,
      "sim": 250.555,
      "disputed": false,
      "dev_pct": 6.619148936170216,
      "tol_pct": 20,
      "gated": true,
      "within": true,
      "note": "Bass channel input plate (V1a), 100k from the preamp rail",
      "dispute_note": ""
    },
    {
      "node": "KB1",
      "chart": 2,
      "sim": 1.932,
      "disputed": false,
      "dev_pct": 3.400000000000003,
      "tol_pct": 20,
      "gated": true,
      "within": true,
      "note": "Bass channel input cathode over 1.5k (25 uF bypass)",
      "dispute_note": ""
    },
    {
      "node": "PB2",
      "chart": 235,
      "sim": 250.555,
      "disputed": false,
      "dev_pct": 6.619148936170216,
      "tol_pct": 20,
      "gated": true,
      "within": true,
      "note": "Bass channel 2nd-stage plate (V1b), 100k from the preamp rail",
      "dispute_note": ""
    },
    {
      "node": "KB2",
      "chart": 2,
      "sim": 1.932,
      "disputed": false,
      "dev_pct": 3.400000000000003,
      "tol_pct": 20,
      "gated": true,
      "within": true,
      "note": "Bass channel 2nd-stage cathode over 1.5k (25 uF bypass)",
      "dispute_note": ""
    },
    {
      "node": "PB3",
      "chart": 240,
      "sim": 250.555,
      "disputed": false,
      "dev_pct": 4.39791666666667,
      "tol_pct": 20,
      "gated": true,
      "within": true,
      "note": "Bass channel driver plate (V3b), 100k with 0.003 uF across it",
      "dispute_note": ""
    },
    {
      "node": "KB3",
      "chart": 1.9,
      "sim": 1.932,
      "disputed": false,
      "dev_pct": 1.6842105263157912,
      "tol_pct": 20,
      "gated": true,
      "within": true,
      "note": "Bass channel driver cathode over 1.5k — the one preamp cathode with no bypass can",
      "dispute_note": ""
    },
    {
      "node": "PN1",
      "chart": 250,
      "sim": 250.555,
      "disputed": false,
      "dev_pct": 0.2220000000000027,
      "tol_pct": 20,
      "gated": true,
      "within": true,
      "note": "Normal channel input plate (V2a), 100k from the preamp rail",
      "dispute_note": ""
    },
    {
      "node": "KN1",
      "chart": 1.8,
      "sim": 1.932,
      "disputed": false,
      "dev_pct": 7.333333333333328,
      "tol_pct": 20,
      "gated": true,
      "within": true,
      "note": "Normal channel input cathode over 1.5k (25 uF bypass)",
      "dispute_note": ""
    },
    {
      "node": "PN2",
      "chart": 250,
      "sim": 250.555,
      "disputed": false,
      "dev_pct": 0.2220000000000027,
      "tol_pct": 20,
      "gated": true,
      "within": true,
      "note": "Normal channel 2nd-stage plate (V2b), 100k from the preamp rail",
      "dispute_note": ""
    },
    {
      "node": "KN2",
      "chart": 1.8,
      "sim": 1.932,
      "disputed": false,
      "dev_pct": 7.333333333333328,
      "tol_pct": 20,
      "gated": true,
      "within": true,
      "note": "Normal channel 2nd-stage cathode over 1.5k (25 uF bypass)",
      "dispute_note": ""
    },
    {
      "node": "PPA",
      "chart": 220,
      "sim": 234.853,
      "disputed": false,
      "dev_pct": 6.7513636363636405,
      "tol_pct": 20,
      "gated": true,
      "within": true,
      "note": "PI plate, 82k (hot) side",
      "dispute_note": ""
    },
    {
      "node": "PPB",
      "chart": 205,
      "sim": 228.782,
      "disputed": false,
      "dev_pct": 11.600975609756103,
      "tol_pct": 20,
      "gated": true,
      "within": true,
      "note": "PI plate, 100k (cold) side",
      "dispute_note": ""
    },
    {
      "node": "KPI",
      "chart": 95,
      "sim": 88.919,
      "disputed": false,
      "dev_pct": 6.40105263157895,
      "tol_pct": 20,
      "gated": true,
      "within": true,
      "note": "PI joined cathodes, above the 470 Ohm",
      "dispute_note": ""
    },
    {
      "node": "JPI",
      "chart": 93,
      "sim": 87.067,
      "disputed": false,
      "dev_pct": 6.379569892473127,
      "tol_pct": 20,
      "gated": true,
      "within": true,
      "note": "PI tail junction (470 Ohm / 22k), grid-leak return",
      "dispute_note": ""
    },
    {
      "node": "NFB",
      "chart": null,
      "sim": 0.394,
      "disputed": false,
      "dev_pct": null,
      "tol_pct": 5,
      "gated": false,
      "within": null,
      "note": "negative-feedback node — the 22k tail's return, working into the 100 Ohm to ground. Not printed on the chart; reported for information",
      "dispute_note": ""
    }
  ],
  "checks": [
    {
      "id": "dc",
      "title": "DC operating point",
      "status": "Verified",
      "summary": "18 reference nodes are within tolerance. Maintainer verification is recorded for 2026-08-13; 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: FUSE. 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, V2, V3, V4.",
        "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": "Checked",
      "summary": "10 capacitor markings agree with the model's voltage ordering.",
      "details": [
        "This check uses DC voltage ordering; source review establishes markings the model cannot decide."
      ],
      "tone": "checked"
    }
  ],
  "corrections": [
    {
      "id": "aa864-driver-cap-2026-10-03",
      "date": "2026-10-03",
      "amps": [
        "aa864-bassman"
      ],
      "title": "AA864: driver plate capacitor is .003 µF",
      "description": "The capacitor across the Bass channel driver's 100 kΩ plate resistor is lettered .003 µF on the layout drawing. We listed .005 µF. The roll-off it sets is near 1.3 kHz rather than 800 Hz.",
      "commit": "df3c31898371a92f63359c0047af9d8d22984516",
      "url": "https://github.com/TheAnalogMaker/circuit-codex/commit/df3c31898371a92f63359c0047af9d8d22984516"
    },
    {
      "id": "aa864-input-leaks-2026-10-03",
      "date": "2026-10-03",
      "amps": [
        "aa864-bassman"
      ],
      "title": "AA864: input 1 MΩ resistors sit at jack 1",
      "description": "The factory drawing connects each channel's 1 MΩ input resistor to jack 1's tip, before that jack's 68 kΩ resistor. We drew it on the grid side on both the schematic and the board. Both are corrected.",
      "commit": "df3c31898371a92f63359c0047af9d8d22984516",
      "url": "https://github.com/TheAnalogMaker/circuit-codex/commit/df3c31898371a92f63359c0047af9d8d22984516"
    },
    {
      "id": "aa864-mains-2026-10-03",
      "date": "2026-10-03",
      "amps": [
        "aa864-bassman"
      ],
      "title": "AA864: fuse and power switch are on opposite mains legs",
      "description": "The factory drawings put the 2 A slow-blow fuse on one leg of the mains and the AC switch on the other. Our schematic put them in series on one leg, and our board drew the fuse across the transformer primary. Both are corrected.",
      "commit": "df3c31898371a92f63359c0047af9d8d22984516",
      "url": "https://github.com/TheAnalogMaker/circuit-codex/commit/df3c31898371a92f63359c0047af9d8d22984516"
    },
    {
      "id": "aa864-treble-series-2026-10-03",
      "date": "2026-10-03",
      "amps": [
        "aa864-bassman"
      ],
      "title": "AA864: Bass channel treble resistor is 220 kΩ",
      "description": "The resistor between the Bass channel's 250 pF treble capacitor and its treble control is 220 kΩ, as the layout drawing letters it and the schematic agrees. We listed 250 kΩ.",
      "commit": "df3c31898371a92f63359c0047af9d8d22984516",
      "url": "https://github.com/TheAnalogMaker/circuit-codex/commit/df3c31898371a92f63359c0047af9d8d22984516"
    }
  ],
  "sourceDirectory": "https://github.com/TheAnalogMaker/circuit-codex/tree/ebddc3fd2cf887dca010bbe60487d7391ea6c052/amps/aa864-bassman"
}