{
  "format": "circuit-codex-reference",
  "version": 1,
  "id": "5f6",
  "url": "https://circuitcodex.com/amps/5f6/",
  "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": "5f6",
    "name_style": "Tweed Bassman-style",
    "family": "tweed",
    "era": {
      "start": 1957,
      "end": 1958
    },
    "wattage": 40,
    "tubes": [
      "12AY7",
      "12AX7",
      "12AX7",
      5881,
      5881,
      "83"
    ],
    "topology": {
      "rectifier": {
        "kind": "tube",
        "type": "83"
      },
      "bias": "fixed",
      "phase_inverter": "long-tailed-pair",
      "tone_stack": "cathode-follower-fmv"
    },
    "lineage": {
      "derived_from": [
        "5e6a"
      ],
      "influenced": [
        "5f6a"
      ]
    },
    "conventions": {
      "designators": "functional"
    },
    "sources": [
      {
        "desc": "Fender 'Bassman' Model 5F6 drawing (F-EG): every component value AND the printed voltage chart read directly from the published schematic (2026-08-02) — 12AY7 two-channel front end (68k stoppers, 1M leaks, 100k plates, shared 820Ω/250µF cathode), 12AX7 gain stage (100k plate, 820Ω/25µF cathode) direct-coupled to a cathode follower (100k load) feeding the treble/middle/bass stack (56k slope, 250 pF, 2×0.02 µF; 250k/1M/25k pots — the drawing's own wiring re-read 2026-08-03: both the 250 pF and the 56k leave the follower's output, the first 0.02 µF lands on the node shared by the treble pot's lower lug and the bass pot, the bass pot is a rheostat in series down the ladder, the second 0.02 µF feeds the middle pot's WIPER, and the stack's output is the treble wiper alone) whose ground leg runs through the 5 kΩ presence control, 12AX7 long-tailed-pair PI (82k/100k 5% plates, 470Ω + 10k tail to ground, 1M leaks to the tail junction, 47 pF across the plates), 5881 pair fixed-biased at −48 V through 220k leaks with 1500Ω grid stoppers and 100Ω screen resistors, and an 83 mercury-vapour rectifier; rails +432/+430/+385/+325, PT 8087, choke 14684, OT 45249. Not reproduced here; archived at EL34World",
        "url": "https://el34world.com/charts/Schematics/files/Fender/Fender_bassman_5f6.pdf"
      },
      {
        "desc": "Fender 'Bassman' Model 5F6-A drawing (I-EG) — read side by side to establish exactly what the later revision changed: GZ34 in place of the 83, 470Ω 1W screen resistors in place of 100Ω, no output grid stoppers, and the presence control moved out of the tone-stack ground leg to the phase-inverter tail foot. Both drawings print the same rails, transformers and preamp values",
        "url": "https://el34world.com/charts/Schematics/files/Fender/Fender_bassman_5f6a.pdf"
      },
      {
        "desc": "Fender 'Bassman' Model 5F6 layout drawing (F-EG), page 1 — the source for the board-layout drawing on this page: the order in which parts sit on the eyelet board AND the wiring layer (which eyelet each lead leaves, where it lands on the sockets, pots, jacks and transformers — including the tone-pot hookup re-read 2026-08-03: the bass pot's wiper strapped into the treble-pot/bass-cap node, the middle pot's wiper fed from the second 0.02 µF eyelet, the middle pot's foot wired on to the presence pot, and the treble wiper alone leaving for the phase-inverter coupler — and the marked lead colours — PT red/red-yellow HT, yellow 5 V rectifier filament, red-blue bias tap, green + green-yellow heaters; OT blue/brown plate + red centre tap + black/green secondary). The same sheet notes 1 W on both rail droppers and mounts the 1.5 kΩ output grid stoppers, the 100 Ω screen resistors and the 100 kΩ V2A plate load on the tube sockets rather than the board. Redrawn from the published facts, never traced",
        "url": "https://el34world.com/charts/Schematics/files/Fender/Fender_bassman_5f6.pdf"
      },
      {
        "desc": "RCA type 83 data sheet, 7-63 — the mercury-vapour rectifier's characteristics and ratings, and the anchors this corpus's clean-room 83 model is fitted to: tube voltage drop approximately 15 V, rated 225 mA d-c output, 1 A peak per plate, 1550 V peak inverse, condensed-mercury temperature 20–60 °C, 5.0 V / 3.0 A filament",
        "url": "https://frank.pocnet.net/sheets/049/8/83.pdf"
      },
      {
        "desc": "General Electric type 83 data sheet, ET-T464, 2-47 — corroborates the RCA figures and states the design intent behind them: the tube supplies d-c current at essentially constant voltage in spite of rather wide variations in output current",
        "url": "https://frank.pocnet.net/sheets/093/8/83.pdf"
      },
      {
        "desc": "Wikipedia, 'Fender Bassman' — dates the 5F6 to July 1957 and describes it as the revision built around a single 83 mercury-vapour rectifier with a new three-knob tone stack, superseded during 1958 by the 5F6-A, which changed the rectifier to a GZ34 and modified the presence circuit. Neither drawing prints a power rating; the 40 W figure here is the 5F6-A's, carried across because the two circuits share the power transformer (8087), choke (14684), output transformer (45249), 5881 pair, printed rails and printed bias voltage",
        "url": "https://en.wikipedia.org/wiki/Fender_Bassman"
      }
    ],
    "verification": {
      "status": "verified",
      "date": "2026-08-02T00:00:00.000Z",
      "max_deviation_pct": 9.6
    },
    "contributors": [
      "TheAnalogMaker"
    ]
  },
  "parts": {
    "notes": "Resistor and potentiometer designators are shared with the 5F6-A, so the two revisions read side by side. The capacitor numbers are not, and cannot be: the 5F6 carries two capacitors the 5F6-A does not — the 25 µF across V2A's cathode resistor (C4) and the 47 pF across the phase-inverter plates (C12) — so from C4 onward the two runs diverge and the same C number names a different part on each page. Read a capacitor by its role, not by its number, when comparing the revisions. Both pages draw four input jacks, two per channel, each with its own 68 kΩ stopper (R1s/R3s Bright, R2s/R4s Normal), and hang each channel's 1 MΩ leak from jack 1's tip. Speaker jacks, the a-c line and ground switch, the pilot lamp and the 0.05 µF · 600 V from the standby switch's rectifier side to ground are on the chassis, not the board, and are not listed. The output transformer keeps the 5F6-A's T3 for the same reason, which is why no T1 or T2 appears; the power transformer, like the other off-board parts, is listed without a designator.",
    "items": [
      {
        "ref": "R1s",
        "part": "Carbon comp resistor",
        "value": "68 kΩ · ½ W",
        "role": "Bright-channel grid stopper (jack 1)"
      },
      {
        "ref": "R3s",
        "part": "Carbon comp resistor",
        "value": "68 kΩ · ½ W",
        "role": "Bright-channel grid stopper (jack 2)"
      },
      {
        "ref": "R2s",
        "part": "Carbon comp resistor",
        "value": "68 kΩ · ½ W",
        "role": "Normal-channel grid stopper (jack 1)"
      },
      {
        "ref": "R4s",
        "part": "Carbon comp resistor",
        "value": "68 kΩ · ½ W",
        "role": "Normal-channel grid stopper (jack 2)"
      },
      {
        "ref": "RG1",
        "part": "Carbon comp resistor",
        "value": "1 MΩ · ½ W",
        "role": "Bright input grid leak"
      },
      {
        "ref": "RG2",
        "part": "Carbon comp resistor",
        "value": "1 MΩ · ½ W",
        "role": "Normal input grid leak"
      },
      {
        "ref": "RL1",
        "part": "Carbon comp resistor",
        "value": "100 kΩ · ½ W",
        "role": "V1A plate load"
      },
      {
        "ref": "RL2",
        "part": "Carbon comp resistor",
        "value": "100 kΩ · ½ W",
        "role": "V1B plate load"
      },
      {
        "ref": "RK1",
        "part": "Carbon comp resistor",
        "value": "820 Ω · ½ W",
        "role": "Shared 12AY7 cathode bias"
      },
      {
        "ref": "C3",
        "part": "Electrolytic capacitor",
        "value": "250 µF · 6 V",
        "role": "Shared 12AY7 cathode bypass"
      },
      {
        "ref": "C1",
        "part": "Coupling capacitor",
        "value": "0.02 µF · 400 V",
        "role": "V1A → bright volume"
      },
      {
        "ref": "C2",
        "part": "Coupling capacitor",
        "value": "0.02 µF · 400 V",
        "role": "V1B → normal volume"
      },
      {
        "ref": "VR1",
        "part": "Audio-taper potentiometer",
        "value": "1 MΩ",
        "role": "Bright volume (100 pF bright cap across it)"
      },
      {
        "ref": "VR2",
        "part": "Audio-taper potentiometer",
        "value": "1 MΩ",
        "role": "Normal volume"
      },
      {
        "ref": "RM1",
        "part": "Carbon comp resistor",
        "value": "270 kΩ · ½ W",
        "role": "Bright-channel mixer"
      },
      {
        "ref": "RM2",
        "part": "Carbon comp resistor",
        "value": "270 kΩ · ½ W",
        "role": "Normal-channel mixer"
      },
      {
        "ref": "RL3",
        "part": "Carbon comp resistor",
        "value": "100 kΩ · ½ W",
        "role": "V2A plate load"
      },
      {
        "ref": "RK2",
        "part": "Carbon comp resistor",
        "value": "820 Ω · ½ W",
        "role": "V2A cathode bias"
      },
      {
        "ref": "C4",
        "part": "Electrolytic capacitor",
        "value": "25 µF · 25 V",
        "role": "V2A cathode bypass"
      },
      {
        "ref": "RKCF",
        "part": "Carbon comp resistor",
        "value": "100 kΩ · ½ W",
        "role": "Cathode-follower load"
      },
      {
        "ref": "RSL",
        "part": "Carbon comp resistor",
        "value": "56 kΩ · ½ W",
        "role": "Tone-stack slope resistor"
      },
      {
        "ref": "C5",
        "part": "Mica capacitor",
        "value": "250 pF",
        "role": "Tone stack — treble"
      },
      {
        "ref": "VR3",
        "part": "Linear potentiometer",
        "value": "250 kΩ",
        "role": "Treble"
      },
      {
        "ref": "C6",
        "part": "Film capacitor",
        "value": "0.02 µF · 400 V",
        "role": "Tone stack — slope junction to the treble/bass node"
      },
      {
        "ref": "C7",
        "part": "Film capacitor",
        "value": "0.02 µF · 400 V",
        "role": "Tone stack — slope junction to the middle wiper"
      },
      {
        "ref": "VR4",
        "part": "Audio-taper potentiometer",
        "value": "1 MΩ",
        "role": "Bass (wired as a variable resistor)"
      },
      {
        "ref": "VR5",
        "part": "Linear potentiometer",
        "value": "25 kΩ",
        "role": "Middle"
      },
      {
        "ref": "VR6",
        "part": "Linear potentiometer",
        "value": "5 kΩ",
        "role": "Presence — in series with the tone stack's ground leg"
      },
      {
        "ref": "C13",
        "part": "Film capacitor",
        "value": "0.1 µF · 200 V",
        "role": "Presence wiper to ground"
      },
      {
        "ref": "RNF",
        "part": "Carbon comp resistor",
        "value": "27 kΩ · ½ W",
        "role": "Negative feedback, speaker output → tone-stack ground leg"
      },
      {
        "ref": "C10",
        "part": "Coupling capacitor",
        "value": "0.02 µF · 400 V",
        "role": "Treble wiper → phase-inverter grid"
      },
      {
        "ref": "RGA",
        "part": "Carbon comp resistor",
        "value": "1 MΩ · ½ W",
        "role": "PI grid leak (V3A), returned to the tail junction"
      },
      {
        "ref": "RGB",
        "part": "Carbon comp resistor",
        "value": "1 MΩ · ½ W",
        "role": "PI grid leak (V3B), returned to the tail junction"
      },
      {
        "ref": "RLA",
        "part": "Carbon comp resistor",
        "value": "82 kΩ · ½ W · 5%",
        "role": "PI plate load (V3A)"
      },
      {
        "ref": "RLB",
        "part": "Carbon comp resistor",
        "value": "100 kΩ · ½ W · 5%",
        "role": "PI plate load (V3B)"
      },
      {
        "ref": "RTAIL",
        "part": "Carbon comp resistor",
        "value": "470 Ω · ½ W",
        "role": "PI tail bias"
      },
      {
        "ref": "RT2",
        "part": "Carbon comp resistor",
        "value": "10 kΩ · ½ W",
        "role": "PI tail (junction → ground)"
      },
      {
        "ref": "C11",
        "part": "Film capacitor",
        "value": "0.1 µF · 200 V",
        "role": "V3B grid AC-ground"
      },
      {
        "ref": "C12",
        "part": "Mica capacitor",
        "value": "47 pF",
        "role": "Across the two PI plates"
      },
      {
        "ref": "C8",
        "part": "Coupling capacitor",
        "value": "0.1 µF · 400 V",
        "role": "PI → V4 grid"
      },
      {
        "ref": "C9",
        "part": "Coupling capacitor",
        "value": "0.1 µF · 400 V",
        "role": "PI → V5 grid"
      },
      {
        "ref": "RGL1",
        "part": "Carbon comp resistor",
        "value": "220 kΩ · ½ W",
        "role": "V4 grid leak, from the −48 V bias line"
      },
      {
        "ref": "RGL2",
        "part": "Carbon comp resistor",
        "value": "220 kΩ · ½ W",
        "role": "V5 grid leak, from the −48 V bias line"
      },
      {
        "ref": "RGS1",
        "part": "Carbon comp resistor",
        "value": "1.5 kΩ · ½ W",
        "role": "V4 grid stopper"
      },
      {
        "ref": "RGS2",
        "part": "Carbon comp resistor",
        "value": "1.5 kΩ · ½ W",
        "role": "V5 grid stopper"
      },
      {
        "ref": "RS1",
        "part": "Carbon comp resistor",
        "value": "100 Ω · ½ W",
        "role": "V4 screen resistor"
      },
      {
        "ref": "RS2",
        "part": "Carbon comp resistor",
        "value": "100 Ω · ½ W",
        "role": "V5 screen resistor"
      },
      {
        "ref": "RD1",
        "part": "Carbon comp resistor",
        "value": "4.7 kΩ · 1 W",
        "role": "Rail dropper B+2 → B+3 (printed 1 W)"
      },
      {
        "ref": "RD2",
        "part": "Carbon comp resistor",
        "value": "10 kΩ · 1 W",
        "role": "Rail dropper B+3 → B+4 (printed 1 W)"
      },
      {
        "ref": "L1",
        "part": "Filter choke",
        "value": "Fender 14684",
        "role": "B+1 → B+2 (screens)"
      },
      {
        "ref": "C14",
        "part": "Electrolytic capacitor",
        "value": "20 µF · 600 V",
        "role": "Filter, B+1"
      },
      {
        "ref": "C15",
        "part": "Electrolytic capacitor",
        "value": "20 µF · 600 V",
        "role": "Filter, B+1 (second, in parallel with C14)"
      },
      {
        "ref": "C16",
        "part": "Electrolytic capacitor",
        "value": "20 µF · 600 V",
        "role": "Filter, B+2"
      },
      {
        "ref": "C17",
        "part": "Electrolytic capacitor",
        "value": "20 µF · 600 V",
        "role": "Filter, B+3"
      },
      {
        "ref": "C18",
        "part": "Electrolytic capacitor",
        "value": "8 µF · 450 V",
        "role": "Filter, B+4"
      },
      {
        "ref": "D1",
        "part": "Rectifier (bias)",
        "value": "selenium · silicon diode in modern builds",
        "role": "Bias supply rectifier"
      },
      {
        "ref": "RB1",
        "part": "Carbon comp resistor",
        "value": "15 kΩ · ½ W",
        "role": "Bias supply series resistor"
      },
      {
        "ref": "RB2",
        "part": "Carbon comp resistor",
        "value": "56 kΩ · ½ W",
        "role": "Bias supply bleeder"
      },
      {
        "ref": "C19",
        "part": "Electrolytic capacitor",
        "value": "8 µF · 150 V",
        "role": "Bias supply reservoir, rectifier side of the 15 kΩ"
      },
      {
        "ref": "C20",
        "part": "Electrolytic capacitor",
        "value": "8 µF · 150 V",
        "role": "Bias supply filter, −48 V line"
      },
      {
        "ref": "V1",
        "part": "Preamp tube",
        "value": "12AY7",
        "role": "Both input stages (V1A/V1B)"
      },
      {
        "ref": "V2",
        "part": "Preamp tube",
        "value": "12AX7",
        "role": "Second stage + cathode follower (V2A/V2B)"
      },
      {
        "ref": "V3",
        "part": "Preamp tube",
        "value": "12AX7",
        "role": "Long-tailed-pair phase inverter (V3A/V3B)"
      },
      {
        "ref": "V4",
        "part": "Power tube",
        "value": "5881",
        "role": "Push-pull output (upper)"
      },
      {
        "ref": "V5",
        "part": "Power tube",
        "value": "5881",
        "role": "Push-pull output (lower)"
      },
      {
        "ref": "V6",
        "part": "Rectifier tube",
        "value": "83",
        "role": "Full-wave mercury-vapour rectifier (V6A/V6B)"
      },
      {
        "ref": "T3",
        "part": "Output transformer",
        "value": "Fender 45249",
        "role": "Push-pull output into four speakers on four parallel jacks (neither page prints an impedance)"
      },
      {
        "ref": "—",
        "part": "Power transformer",
        "value": "Fender 8087 · 325-0-325 V",
        "role": "HT + heaters + rectifier filament"
      },
      {
        "ref": "—",
        "part": "Mica capacitor",
        "value": "100 pF",
        "role": "Bright cap across VR1"
      }
    ]
  },
  "publishedVoltages": {
    "source": "Fender 5F6 (F-EG) drawing, printed voltages: rails +432/+430/+385/+325, bias -48; 12AY7 plates +150, cathode +2.5; V2A plate +180, cathode +1.2, cathode follower +180; PI grids +22/+23, cathodes +34, tail junction +32.5, PI plates +235/+230",
    "nodes": {
      "BP2": {
        "chart": 430,
        "tol_pct": 8,
        "note": "screens node after the choke (DCR estimated at 130 Ω)"
      },
      "BP3": {
        "chart": 385,
        "tol_pct": 8,
        "note": "PI supply node after the 4.7 kΩ dropper"
      },
      "BP4": {
        "chart": 325,
        "tol_pct": 8,
        "note": "preamp node after the 10 kΩ dropper"
      },
      "PAY1": {
        "chart": 150,
        "tol_pct": 20,
        "note": "12AY7 plate (bright channel), printed pin value"
      },
      "PAY2": {
        "chart": 150,
        "tol_pct": 20,
        "note": "12AY7 plate (normal channel)"
      },
      "KAY": {
        "chart": 2.5,
        "tol_pct": 20,
        "note": "shared 12AY7 cathode, 820 Ω"
      },
      "P2A": {
        "chart": 180,
        "tol_pct": 20,
        "note": "V2A plate = cathode-follower grid (direct-coupled)"
      },
      "K2A": {
        "chart": 1.2,
        "tol_pct": 20,
        "note": "V2A cathode, 820 Ω with a 25 µF bypass"
      },
      "KCF": {
        "chart": 180,
        "tol_pct": 20,
        "note": "cathode-follower output, printed +180"
      },
      "PPIA": {
        "chart": 235,
        "tol_pct": 20,
        "note": "PI plate, 82k 5% side"
      },
      "PPIB": {
        "chart": 230,
        "tol_pct": 20,
        "note": "PI plate, 100k 5% side"
      },
      "KPI": {
        "chart": 34,
        "tol_pct": 20,
        "note": "PI cathodes above the 470 Ω tail resistor"
      },
      "JPI": {
        "chart": 32.5,
        "tol_pct": 20,
        "note": "tail junction (grid-leak return), above the 10 kΩ to ground"
      },
      "GPIA": {
        "chart": 22,
        "tol_pct": 20,
        "disputed": true,
        "dispute_note": "The chart contradicts its own topology. This grid reaches the tail junction through a 1 MΩ leak and has no other DC path, so with no grid current it must sit at the junction's own printed +32.5 V. The printed 22 V is 68% of that — the fraction a 1 MΩ source reads into a meter of roughly 2 MΩ input resistance (22 = 32.5 × 2.1/3.1), which is a 20,000 Ω/V moving-coil voltmeter on its 100 V range rather than the electronic voltmeter the drawing's notice specifies. Simulation follows the topology."
      },
      "GPIB": {
        "chart": 23,
        "tol_pct": 20,
        "disputed": true,
        "dispute_note": "The other half of the same contradiction — see GPIA. Printed 23 V against the same +32.5 V junction is 71%, the same ≈2 MΩ meter loading on the second 1 MΩ leak."
      },
      "S51": {
        "chart": null,
        "note": "informational — 5881 screen after its 100 Ω resistor"
      },
      "G51": {
        "chart": -48,
        "tol_pct": 8,
        "note": "fixed bias via a 220 kΩ leak and a 1.5 kΩ grid stopper from the −48 V supply"
      }
    }
  },
  "operatingPoint": [
    {
      "node": "BP2",
      "chart": 430,
      "sim": 430.517,
      "disputed": false,
      "dev_pct": 0.12023255813953394,
      "tol_pct": 8,
      "gated": true,
      "within": true,
      "note": "screens node after the choke (DCR estimated at 130 Ω)",
      "dispute_note": ""
    },
    {
      "node": "BP3",
      "chart": 385,
      "sim": 386.083,
      "disputed": false,
      "dev_pct": 0.28129870129870826,
      "tol_pct": 8,
      "gated": true,
      "within": true,
      "note": "PI supply node after the 4.7 kΩ dropper",
      "dispute_note": ""
    },
    {
      "node": "BP4",
      "chart": 325,
      "sim": 322.256,
      "disputed": false,
      "dev_pct": 0.844307692307701,
      "tol_pct": 8,
      "gated": true,
      "within": true,
      "note": "preamp node after the 10 kΩ dropper",
      "dispute_note": ""
    },
    {
      "node": "PAY1",
      "chart": 150,
      "sim": 164.459,
      "disputed": false,
      "dev_pct": 9.639333333333337,
      "tol_pct": 20,
      "gated": true,
      "within": true,
      "note": "12AY7 plate (bright channel), printed pin value",
      "dispute_note": ""
    },
    {
      "node": "PAY2",
      "chart": 150,
      "sim": 164.459,
      "disputed": false,
      "dev_pct": 9.639333333333337,
      "tol_pct": 20,
      "gated": true,
      "within": true,
      "note": "12AY7 plate (normal channel)",
      "dispute_note": ""
    },
    {
      "node": "KAY",
      "chart": 2.5,
      "sim": 2.588,
      "disputed": false,
      "dev_pct": 3.520000000000003,
      "tol_pct": 20,
      "gated": true,
      "within": true,
      "note": "shared 12AY7 cathode, 820 Ω",
      "dispute_note": ""
    },
    {
      "node": "P2A",
      "chart": 180,
      "sim": 181.6,
      "disputed": false,
      "dev_pct": 0.8888888888888857,
      "tol_pct": 20,
      "gated": true,
      "within": true,
      "note": "V2A plate = cathode-follower grid (direct-coupled)",
      "dispute_note": ""
    },
    {
      "node": "K2A",
      "chart": 1.2,
      "sim": 1.153,
      "disputed": false,
      "dev_pct": 3.916666666666661,
      "tol_pct": 20,
      "gated": true,
      "within": true,
      "note": "V2A cathode, 820 Ω with a 25 µF bypass",
      "dispute_note": ""
    },
    {
      "node": "KCF",
      "chart": 180,
      "sim": 182.018,
      "disputed": false,
      "dev_pct": 1.1211111111111114,
      "tol_pct": 20,
      "gated": true,
      "within": true,
      "note": "cathode-follower output, printed +180",
      "dispute_note": ""
    },
    {
      "node": "PPIA",
      "chart": 235,
      "sim": 252.374,
      "disputed": false,
      "dev_pct": 7.3931914893617,
      "tol_pct": 20,
      "gated": true,
      "within": true,
      "note": "PI plate, 82k 5% side",
      "dispute_note": ""
    },
    {
      "node": "PPIB",
      "chart": 230,
      "sim": 241.997,
      "disputed": false,
      "dev_pct": 5.216086956521745,
      "tol_pct": 20,
      "gated": true,
      "within": true,
      "note": "PI plate, 100k 5% side",
      "dispute_note": ""
    },
    {
      "node": "KPI",
      "chart": 34,
      "sim": 32.158,
      "disputed": false,
      "dev_pct": 5.417647058823525,
      "tol_pct": 20,
      "gated": true,
      "within": true,
      "note": "PI cathodes above the 470 Ω tail resistor",
      "dispute_note": ""
    },
    {
      "node": "JPI",
      "chart": 32.5,
      "sim": 30.715,
      "disputed": false,
      "dev_pct": 5.492307692307693,
      "tol_pct": 20,
      "gated": true,
      "within": true,
      "note": "tail junction (grid-leak return), above the 10 kΩ to ground",
      "dispute_note": ""
    },
    {
      "node": "GPIA",
      "chart": 22,
      "sim": 30.715,
      "disputed": true,
      "dev_pct": 39.61363636363636,
      "tol_pct": 20,
      "gated": false,
      "within": null,
      "note": "",
      "dispute_note": "The chart contradicts its own topology. This grid reaches the tail junction through a 1 MΩ leak and has no other DC path, so with no grid current it must sit at the junction's own printed +32.5 V. The printed 22 V is 68% of that — the fraction a 1 MΩ source reads into a meter of roughly 2 MΩ input resistance (22 = 32.5 × 2.1/3.1), which is a 20,000 Ω/V moving-coil voltmeter on its 100 V range rather than the electronic voltmeter the drawing's notice specifies. Simulation follows the topology."
    },
    {
      "node": "GPIB",
      "chart": 23,
      "sim": 30.715,
      "disputed": true,
      "dev_pct": 33.54347826086956,
      "tol_pct": 20,
      "gated": false,
      "within": null,
      "note": "",
      "dispute_note": "The other half of the same contradiction — see GPIA. Printed 23 V against the same +32.5 V junction is 71%, the same ≈2 MΩ meter loading on the second 1 MΩ leak."
    },
    {
      "node": "S51",
      "chart": null,
      "sim": 430.42,
      "disputed": false,
      "dev_pct": null,
      "tol_pct": 5,
      "gated": false,
      "within": null,
      "note": "informational — 5881 screen after its 100 Ω resistor",
      "dispute_note": ""
    },
    {
      "node": "G51",
      "chart": -48,
      "sim": -48,
      "disputed": false,
      "dev_pct": 0,
      "tol_pct": 8,
      "gated": true,
      "within": true,
      "note": "fixed bias via a 220 kΩ leak and a 1.5 kΩ grid stopper from the −48 V supply",
      "dispute_note": ""
    }
  ],
  "checks": [
    {
      "id": "dc",
      "title": "DC operating point",
      "status": "Verified",
      "summary": "14 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.",
        "2 disputed nodes are excluded from the tolerance result; their reasoning is listed in the operating-point table.",
        "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.",
        "4 sheet-only parts are explicitly excluded: C14, C15, C16, C17. 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.",
        "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": "5 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": "5f6-input-stoppers-2026-10-03",
      "date": "2026-10-03",
      "amps": [
        "5f6"
      ],
      "title": "5F6: each input jack has its own 68 kΩ stopper",
      "description": "The factory drawing shows four input jacks, each with its own 68 kΩ resistor. We showed one per channel and noted the second as a simplification. Both are now drawn and listed.",
      "commit": "a13991970420e87d1300d23ee27aa1921aa91b39",
      "url": "https://github.com/TheAnalogMaker/circuit-codex/commit/a13991970420e87d1300d23ee27aa1921aa91b39"
    },
    {
      "id": "5f6-ot-impedance-2026-10-03",
      "date": "2026-10-03",
      "amps": [
        "5f6"
      ],
      "title": "5F6 output-transformer impedance and tone-control notes",
      "description": "The parts list no longer gives the output transformer a 2 Ω secondary; neither factory page prints an impedance. The notes now describe the bass control's wiring as the layout drawing shows it, and the treble control carries the linear taper the layout prints.",
      "commit": "70057f6673a4adcebe7435c12f0a649deb3a874c",
      "url": "https://github.com/TheAnalogMaker/circuit-codex/commit/70057f6673a4adcebe7435c12f0a649deb3a874c"
    }
  ],
  "sourceDirectory": "https://github.com/TheAnalogMaker/circuit-codex/tree/ebddc3fd2cf887dca010bbe60487d7391ea6c052/amps/5f6"
}