{
  "format": "circuit-codex-reference",
  "version": 1,
  "id": "5f8a",
  "url": "https://circuitcodex.com/amps/5f8a/",
  "attribution": "The Analog Maker / Circuit Codex",
  "license": "https://creativecommons.org/licenses/by-sa/4.0/",
  "revision": "195289eab0b0e41029bffd6e34b65f01a84e553b",
  "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": "5f8a",
    "name_style": "High-power Tweed Twin-style",
    "family": "tweed",
    "era": {
      "start": 1958,
      "end": 1960
    },
    "wattage": 80,
    "tubes": [
      "12AY7",
      "12AX7",
      "12AX7",
      5881,
      5881,
      5881,
      5881,
      "GZ34"
    ],
    "topology": {
      "rectifier": {
        "kind": "tube",
        "type": "GZ34"
      },
      "bias": "fixed",
      "phase_inverter": "long-tailed-pair",
      "tone_stack": "cathode-follower-fmv"
    },
    "lineage": {
      "derived_from": [],
      "influenced": []
    },
    "conventions": {
      "designators": "functional",
      "notation": "us"
    },
    "sources": [
      {
        "desc": "Fender 'Twin-Amp' Model 5F8-A schematic, drawing code I-EG: every component value AND the printed voltage chart read directly from the published sheet (2026-09-09). Two channels of two jacks (68 kΩ stoppers, 1 MΩ leaks) into a 12AY7 (100 kΩ plates, shared 820 Ω/250 µF cathode); 1 MΩ volume pots with a 100 pF bright cap; 270 kΩ mixers into a 12AX7 stage (100 kΩ plate, 820 Ω unbypassed cathode) direct-coupled to a cathode follower (100 kΩ load) feeding the treble/middle/bass stack (56 kΩ slope, 250 pF, 2 × 0.02 µF; 250 kΩ/1 MΩ/25 kΩ pots); 12AX7 long-tailed-pair PI (82 kΩ/100 kΩ 5% plates, 470 Ω + 10 kΩ tail, 1 MΩ leaks to the tail junction, 47 pF across the plates, 0.1 µF grid-B AC ground); four 5881s in two parallel pairs, fixed-biased at −41 V through 220 kΩ leaks with a 1500 Ω stopper between each pair's grids and 470 Ω 1 W screen resistors; 56 kΩ feedback from the speaker and a 5 kΩ presence pot at the tail foot; GZ34 rectifier with a standby switch. Rails +397/+395/+355/+295, PT 7993 (300-0-300 V AC), choke 14684, OT 45268. Provenance: this copy carries the sheet as a 1506 × 841 raster, roughly 100 ppi at sheet size. The topology and every component value on this page were read from it and are legible at that resolution; none of the voltage-chart figures were, because its chart digits do not resolve — see the third source. Not reproduced here; archived at Schematic Heaven",
        "url": "https://schematicheaven.net/fenderamps/twin_5f8a_schem.pdf"
      },
      {
        "desc": "Fender 'Twin-Amp' Model 5F8-A layout drawing (I-EG), page 2 of the same sheet — 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 and where it lands on the sockets, pots, jacks and transformers), the pot tapers (5 kΩ lin presence, 25 kΩ lin middle, 1 MΩ aud bass, 250 kΩ lin treble, 1 MΩ aud volumes, the 100 pF bright cap mounted on the bright volume pot), the marked transformer lead colours, and the sheet's own note that all resistors are ½ W 10% unless otherwise marked — which is where the 1 W on both rail droppers is read. Redrawn from the published facts, never traced. Same 1506 × 841 raster as above: part order and lead routing are legible at it, and no voltage was read from it",
        "url": "https://schematicheaven.net/fenderamps/twin_5f8a_schem.pdf"
      },
      {
        "desc": "The same I-EG schematic and layout as archived at EL34World, captured by the Internet Archive at 693 ppi (6368 × 3218) — 4.2 times the linear resolution of the Schematic Heaven copy's 1506 × 841, about sixteen times the pixel count. Provenance: every voltage on this page — the four rails, the bias line and all eleven tube-pin figures in the operating-point table — was read from this capture and from no other copy. It is not a confirmation of figures read elsewhere: the coarser copy cannot resolve those digits at all, and read from it the two figures either side of the choke come out as +375/+377 where this capture letters +395/+397, and the phase-inverter cathode as +22.5 V where this capture letters +28.5 V. The circuit corroborates the higher-resolution reading: that cathode has to sit above the +27 V tail junction, because its current reaches the junction through the 470 Ω",
        "url": "https://web.archive.org/web/2020id_/https://el34world.com/charts/Schematics/files/Fender/Fender_twin_5f8a.pdf"
      },
      {
        "desc": "Wikipedia, 'Fender Twin' — the source for the production span and the power rating, neither of which the drawing prints: the Twin was modified in 1957 to four 5881 power tubes with a long-tailed-pair phase inverter for an increase to 80 W, and the 5F8-A was released in 1958 and produced into early 1960",
        "url": "https://en.wikipedia.org/wiki/Fender_Twin"
      }
    ],
    "verification": {
      "status": "draft"
    },
    "added": "2026-09-09T00:00:00.000Z",
    "contributors": [
      "TheAnalogMaker"
    ]
  },
  "parts": {
    "notes": "The sheet's own note reads: all resistors are ½ W 10% unless otherwise marked, so a wattage appears below only where the drawing letters one (470 Ω 1 W screens; 1 W on both rail droppers) and a tolerance only where it letters one (5% on the two phase-inverter plate loads). The drawing shows two jacks on each channel and this schematic draws both, with all four 68 kΩ stoppers. The presence pot and its 0.1 µF wiper cap are chassis wiring, and the negative-feedback resistor mounts on the eyelet board beside the tail's 10 kΩ, as the factory layout places it; all three carry designators (RNF, VR6, C16) and are drawn. The 100 pF bright cap mounts on the bright volume pot's own lugs, inside the tone/volume network the DC model abstracts, so it is listed without a designator and annotated on the schematic rather than drawn.",
    "items": [
      {
        "ref": "R1s",
        "part": "Carbon comp resistor",
        "value": "68 kΩ",
        "role": "Bright channel, jack 1 grid stopper"
      },
      {
        "ref": "R2s",
        "part": "Carbon comp resistor",
        "value": "68 kΩ",
        "role": "Bright channel, jack 2 grid stopper"
      },
      {
        "ref": "R3s",
        "part": "Carbon comp resistor",
        "value": "68 kΩ",
        "role": "Normal channel, jack 1 grid stopper"
      },
      {
        "ref": "R4s",
        "part": "Carbon comp resistor",
        "value": "68 kΩ",
        "role": "Normal channel, jack 2 grid stopper"
      },
      {
        "ref": "RG1",
        "part": "Carbon comp resistor",
        "value": "1 MΩ",
        "role": "Bright input grid leak, at the jacks"
      },
      {
        "ref": "RG2",
        "part": "Carbon comp resistor",
        "value": "1 MΩ",
        "role": "Normal input grid leak, at the jacks"
      },
      {
        "ref": "RL1",
        "part": "Carbon comp resistor",
        "value": "100 kΩ",
        "role": "V1A plate load"
      },
      {
        "ref": "RL2",
        "part": "Carbon comp resistor",
        "value": "100 kΩ",
        "role": "V1B plate load"
      },
      {
        "ref": "RK1",
        "part": "Carbon comp resistor",
        "value": "820 Ω",
        "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",
        "role": "Bright-channel mixer"
      },
      {
        "ref": "RM2",
        "part": "Carbon comp resistor",
        "value": "270 kΩ",
        "role": "Normal-channel mixer"
      },
      {
        "ref": "RL3",
        "part": "Carbon comp resistor",
        "value": "100 kΩ",
        "role": "V2A plate load"
      },
      {
        "ref": "RK2",
        "part": "Carbon comp resistor",
        "value": "820 Ω",
        "role": "V2A cathode bias, unbypassed"
      },
      {
        "ref": "RKCF",
        "part": "Carbon comp resistor",
        "value": "100 kΩ",
        "role": "Cathode-follower load"
      },
      {
        "ref": "RSL",
        "part": "Carbon comp resistor",
        "value": "56 kΩ",
        "role": "Tone-stack slope resistor"
      },
      {
        "ref": "C4",
        "part": "Mica capacitor",
        "value": "250 pF",
        "role": "Tone stack — treble"
      },
      {
        "ref": "VR3",
        "part": "Linear potentiometer",
        "value": "250 kΩ",
        "role": "Treble (the factory layout page marks it 250K LIN.)"
      },
      {
        "ref": "C5",
        "part": "Film capacitor",
        "value": "0.02 µF · 400 V",
        "role": "Tone stack — bass (node B → the treble-lug/bass node)"
      },
      {
        "ref": "C5b",
        "part": "Film capacitor",
        "value": "0.02 µF · 400 V",
        "role": "Tone stack — middle (node B → the middle pot's wiper)"
      },
      {
        "ref": "VR4",
        "part": "Audio-taper potentiometer",
        "value": "1 MΩ",
        "role": "Bass (1M AUD. on the layout page); wired as a rheostat down the ladder"
      },
      {
        "ref": "VR5",
        "part": "Linear potentiometer",
        "value": "25 kΩ",
        "role": "Middle (the second 0.02 µF lands on its wiper; its full track stands in the ground leg)"
      },
      {
        "ref": "C6",
        "part": "Coupling capacitor",
        "value": "0.02 µF · 400 V",
        "role": "Tone stack → phase-inverter grid"
      },
      {
        "ref": "RGA",
        "part": "Carbon comp resistor",
        "value": "1 MΩ",
        "role": "PI grid leak (V3A), returned to the tail junction"
      },
      {
        "ref": "RGB",
        "part": "Carbon comp resistor",
        "value": "1 MΩ",
        "role": "PI grid leak (V3B), returned to the tail junction"
      },
      {
        "ref": "RLA",
        "part": "Carbon comp resistor",
        "value": "82 kΩ · 5%",
        "role": "PI plate load (V3A)"
      },
      {
        "ref": "RLB",
        "part": "Carbon comp resistor",
        "value": "100 kΩ · 5%",
        "role": "PI plate load (V3B)"
      },
      {
        "ref": "RTAIL",
        "part": "Carbon comp resistor",
        "value": "470 Ω",
        "role": "PI tail bias"
      },
      {
        "ref": "RT2",
        "part": "Carbon comp resistor",
        "value": "10 kΩ",
        "role": "PI tail (junction → foot)"
      },
      {
        "ref": "C10",
        "part": "Mica capacitor",
        "value": "47 pF",
        "role": "Across the two PI plates"
      },
      {
        "ref": "C7",
        "part": "Film capacitor",
        "value": "0.1 µF · 200 V",
        "role": "V3B grid AC-ground to the tail foot"
      },
      {
        "ref": "RNF",
        "part": "Carbon comp resistor",
        "value": "56 kΩ",
        "role": "Negative feedback, speaker → the phase-inverter tail foot"
      },
      {
        "ref": "VR6",
        "part": "Linear potentiometer",
        "value": "5 kΩ",
        "role": "Presence — its track from the tail foot to ground, 0.1 µF on the wiper"
      },
      {
        "ref": "C16",
        "part": "Film capacitor",
        "value": "0.1 µF · 200 V",
        "role": "Presence wiper to ground"
      },
      {
        "ref": "C8",
        "part": "Coupling capacitor",
        "value": "0.1 µF · 400 V",
        "role": "PI (V3A) → the V4/V5 output pair"
      },
      {
        "ref": "C9",
        "part": "Coupling capacitor",
        "value": "0.1 µF · 400 V",
        "role": "PI (V3B) → the V6/V7 output pair"
      },
      {
        "ref": "RGL1",
        "part": "Carbon comp resistor",
        "value": "220 kΩ",
        "role": "Grid leak for the V4/V5 pair, from the −41 V bias line"
      },
      {
        "ref": "RGL2",
        "part": "Carbon comp resistor",
        "value": "220 kΩ",
        "role": "Grid leak for the V6/V7 pair, from the −41 V bias line"
      },
      {
        "ref": "RGS1",
        "part": "Carbon comp resistor",
        "value": "1.5 kΩ",
        "role": "Grid stopper between the V4 and V5 grids"
      },
      {
        "ref": "RGS2",
        "part": "Carbon comp resistor",
        "value": "1.5 kΩ",
        "role": "Grid stopper between the V6 and V7 grids"
      },
      {
        "ref": "RS1",
        "part": "Carbon comp resistor",
        "value": "470 Ω · 1 W",
        "role": "V4 screen resistor"
      },
      {
        "ref": "RS2",
        "part": "Carbon comp resistor",
        "value": "470 Ω · 1 W",
        "role": "V5 screen resistor"
      },
      {
        "ref": "RS3",
        "part": "Carbon comp resistor",
        "value": "470 Ω · 1 W",
        "role": "V6 screen resistor"
      },
      {
        "ref": "RS4",
        "part": "Carbon comp resistor",
        "value": "470 Ω · 1 W",
        "role": "V7 screen resistor"
      },
      {
        "ref": "RD1",
        "part": "Power resistor",
        "value": "4.7 kΩ · 1 W",
        "role": "Rail dropper B+2 → B+3"
      },
      {
        "ref": "RD2",
        "part": "Power resistor",
        "value": "10 kΩ · 1 W",
        "role": "Rail dropper B+3 → B+4"
      },
      {
        "ref": "L1",
        "part": "Filter choke",
        "value": "Fender 14684",
        "role": "B+1 → B+2 (screens)"
      },
      {
        "ref": "C11",
        "part": "Electrolytic capacitor",
        "value": "20 µF · 600 V",
        "role": "Filter, B+1"
      },
      {
        "ref": "C11b",
        "part": "Electrolytic capacitor",
        "value": "20 µF · 600 V",
        "role": "Filter, B+1 (the sheet draws two cans on this node)"
      },
      {
        "ref": "C12",
        "part": "Electrolytic capacitor",
        "value": "20 µF · 600 V",
        "role": "Filter, B+2"
      },
      {
        "ref": "C13",
        "part": "Electrolytic capacitor",
        "value": "20 µF · 600 V",
        "role": "Filter, B+3"
      },
      {
        "ref": "C14",
        "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",
        "role": "Bias supply series resistor"
      },
      {
        "ref": "RB2",
        "part": "Carbon comp resistor",
        "value": "56 kΩ",
        "role": "Bias supply bleeder"
      },
      {
        "ref": "C15",
        "part": "Electrolytic capacitor",
        "value": "8 µF · 150 V",
        "role": "Bias supply filter, −41 V line"
      },
      {
        "ref": "C15b",
        "part": "Electrolytic capacitor",
        "value": "8 µF · 150 V",
        "role": "Bias supply reservoir, rectifier side of the 15 kΩ"
      },
      {
        "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": "Output, 82 kΩ side of the inverter (paralleled with V5)"
      },
      {
        "ref": "V5",
        "part": "Power tube",
        "value": "5881",
        "role": "Output, 82 kΩ side of the inverter (paralleled with V4)"
      },
      {
        "ref": "V6",
        "part": "Power tube",
        "value": "5881",
        "role": "Output, 100 kΩ side of the inverter (paralleled with V7)"
      },
      {
        "ref": "V7",
        "part": "Power tube",
        "value": "5881",
        "role": "Output, 100 kΩ side of the inverter (paralleled with V6)"
      },
      {
        "ref": "V8",
        "part": "Rectifier tube",
        "value": "GZ34",
        "role": "Full-wave rectifier (V8A/V8B)"
      },
      {
        "ref": "T3",
        "part": "Output transformer",
        "value": "Fender 45268",
        "role": "Push-pull-parallel output into two speakers; the drawing prints no secondary impedance"
      },
      {
        "ref": "—",
        "part": "Power transformer",
        "value": "Fender 7993 · 300-0-300 V",
        "role": "HT + heaters + rectifier filament"
      },
      {
        "ref": "—",
        "part": "Mica capacitor",
        "value": "100 pF",
        "role": "Bright cap across VR1, mounted on the pot (annotation only on schematic)"
      }
    ]
  },
  "publishedVoltages": {
    "source": "Fender 'Twin-Amp' Model 5F8-A drawing (I-EG), printed voltages: rails +397/+395/+355/+295, bias −41 V; pins 12AY7 +145/+145 and +2.2 shared cathode, V2A +165 plate and +1 cathode, cathode follower +165, PI grids +19/+20, tail junction +27, PI cathodes +28.5, PI plates +230 (82k side) / +225 (100k side)",
    "nodes": {
      "BP2": {
        "chart": 395,
        "tol_pct": 8,
        "note": "screens node after the choke (DCR estimated at 130 Ω)"
      },
      "BP3": {
        "chart": 355,
        "tol_pct": 8,
        "note": "PI supply node after the 4.7 kΩ"
      },
      "BP4": {
        "chart": 295,
        "tol_pct": 8,
        "note": "preamp node after the 10 kΩ dropper"
      },
      "PAY1": {
        "chart": 145,
        "tol_pct": 20,
        "note": "12AY7 plate, bright channel"
      },
      "PAY2": {
        "chart": 145,
        "tol_pct": 20,
        "note": "12AY7 plate, normal channel"
      },
      "KAY": {
        "chart": 2.2,
        "tol_pct": 20,
        "note": "shared 12AY7 cathode, 820 Ω"
      },
      "P2A": {
        "chart": 165,
        "tol_pct": 20,
        "note": "V2A plate = cathode-follower grid (direct-coupled)"
      },
      "K2A": {
        "chart": 1,
        "tol_pct": 20,
        "note": "V2A cathode, 820 Ω unbypassed"
      },
      "KCF": {
        "chart": 165,
        "tol_pct": 20,
        "note": "cathode-follower output; the sheet prints +165 on both sides of the direct coupling, so the follower runs at about −1 V grid-to-cathode"
      },
      "PPIA": {
        "chart": 230,
        "tol_pct": 20,
        "note": "PI plate, 82 kΩ 5% side"
      },
      "PPIB": {
        "chart": 225,
        "tol_pct": 20,
        "note": "PI plate, 100 kΩ 5% side"
      },
      "KPI": {
        "chart": 28.5,
        "tol_pct": 20,
        "disputed": true,
        "dispute_note": "The printed tail figures fit a tail the drawing does not show. The printed plates (+230 V through 82 kΩ and +225 V through 100 kΩ, both off +355 V) carry 1.52 + 1.30 = 2.82 mA, and 2.82 mA through a 10 kΩ returned straight to ground is 28.2 V at the junction and 29.6 V at these cathodes — the printed +27 V and +28.5 V. But the I-EG schematic and layout both land that 10 kΩ on a node of its own, returned to ground through the 56 kΩ feedback resistor and the 5 kΩ presence pot's track in parallel (4.6 kΩ); at the same 2.82 mA that puts the junction at 41.2 V and these cathodes at 42.5 V. Simulation follows the drawn tail."
      },
      "JPI": {
        "chart": 27,
        "tol_pct": 20,
        "disputed": true,
        "dispute_note": "The other half of the same contradiction — see KPI. The printed plates' 2.82 mA through the 10 kΩ alone gives 28.2 V, which fits the printed +27 V only if the 10 kΩ returns to ground; through the drawn foot (56 kΩ ∥ 5 kΩ = 4.6 kΩ) the same current puts the junction at 41.2 V."
      },
      "PRES": {
        "chart": null,
        "note": "informational — the tail's foot, where the 10 kΩ, the 56 kΩ feedback resistor, the presence pot's track and the V3B grid's 0.1 µF meet; the drawing prints no figure here"
      },
      "GA1": {
        "chart": -41,
        "tol_pct": 8,
        "note": "fixed bias via the 220 kΩ leaks from the −41 V supply"
      },
      "SA1": {
        "chart": null,
        "note": "informational — 5881 screen after its 470 Ω; the sheet prints no screen figure"
      }
    }
  },
  "operatingPoint": [
    {
      "node": "BP2",
      "chart": 395,
      "sim": 395.02,
      "disputed": false,
      "dev_pct": 0.005063291139235902,
      "tol_pct": 8,
      "gated": true,
      "within": true,
      "note": "screens node after the choke (DCR estimated at 130 Ω)",
      "dispute_note": ""
    },
    {
      "node": "BP3",
      "chart": 355,
      "sim": 354.694,
      "disputed": false,
      "dev_pct": 0.08619718309858682,
      "tol_pct": 8,
      "gated": true,
      "within": true,
      "note": "PI supply node after the 4.7 kΩ",
      "dispute_note": ""
    },
    {
      "node": "BP4",
      "chart": 295,
      "sim": 296.196,
      "disputed": false,
      "dev_pct": 0.40542372881356825,
      "tol_pct": 8,
      "gated": true,
      "within": true,
      "note": "preamp node after the 10 kΩ dropper",
      "dispute_note": ""
    },
    {
      "node": "PAY1",
      "chart": 145,
      "sim": 151.983,
      "disputed": false,
      "dev_pct": 4.81586206896552,
      "tol_pct": 20,
      "gated": true,
      "within": true,
      "note": "12AY7 plate, bright channel",
      "dispute_note": ""
    },
    {
      "node": "PAY2",
      "chart": 145,
      "sim": 151.983,
      "disputed": false,
      "dev_pct": 4.81586206896552,
      "tol_pct": 20,
      "gated": true,
      "within": true,
      "note": "12AY7 plate, normal channel",
      "dispute_note": ""
    },
    {
      "node": "KAY",
      "chart": 2.2,
      "sim": 2.365,
      "disputed": false,
      "dev_pct": 7.500000000000001,
      "tol_pct": 20,
      "gated": true,
      "within": true,
      "note": "shared 12AY7 cathode, 820 Ω",
      "dispute_note": ""
    },
    {
      "node": "P2A",
      "chart": 165,
      "sim": 166.661,
      "disputed": false,
      "dev_pct": 1.0066666666666675,
      "tol_pct": 20,
      "gated": true,
      "within": true,
      "note": "V2A plate = cathode-follower grid (direct-coupled)",
      "dispute_note": ""
    },
    {
      "node": "K2A",
      "chart": 1,
      "sim": 1.062,
      "disputed": false,
      "dev_pct": 6.2000000000000055,
      "tol_pct": 20,
      "gated": true,
      "within": true,
      "note": "V2A cathode, 820 Ω unbypassed",
      "dispute_note": ""
    },
    {
      "node": "KCF",
      "chart": 165,
      "sim": 167.024,
      "disputed": false,
      "dev_pct": 1.2266666666666672,
      "tol_pct": 20,
      "gated": true,
      "within": true,
      "note": "cathode-follower output; the sheet prints +165 on both sides of the direct coupling, so the follower runs at about −1 V grid-to-cathode",
      "dispute_note": ""
    },
    {
      "node": "PPIA",
      "chart": 230,
      "sim": 236.014,
      "disputed": false,
      "dev_pct": 2.6147826086956565,
      "tol_pct": 20,
      "gated": true,
      "within": true,
      "note": "PI plate, 82 kΩ 5% side",
      "dispute_note": ""
    },
    {
      "node": "PPIB",
      "chart": 225,
      "sim": 226.42,
      "disputed": false,
      "dev_pct": 0.6311111111111055,
      "tol_pct": 20,
      "gated": true,
      "within": true,
      "note": "PI plate, 100 kΩ 5% side",
      "dispute_note": ""
    },
    {
      "node": "KPI",
      "chart": 28.5,
      "sim": 41.115,
      "disputed": true,
      "dev_pct": 44.26315789473685,
      "tol_pct": 20,
      "gated": false,
      "within": null,
      "note": "",
      "dispute_note": "The printed tail figures fit a tail the drawing does not show. The printed plates (+230 V through 82 kΩ and +225 V through 100 kΩ, both off +355 V) carry 1.52 + 1.30 = 2.82 mA, and 2.82 mA through a 10 kΩ returned straight to ground is 28.2 V at the junction and 29.6 V at these cathodes — the printed +27 V and +28.5 V. But the I-EG schematic and layout both land that 10 kΩ on a node of its own, returned to ground through the 56 kΩ feedback resistor and the 5 kΩ presence pot's track in parallel (4.6 kΩ); at the same 2.82 mA that puts the junction at 41.2 V and these cathodes at 42.5 V. Simulation follows the drawn tail."
    },
    {
      "node": "JPI",
      "chart": 27,
      "sim": 39.832,
      "disputed": true,
      "dev_pct": 47.525925925925925,
      "tol_pct": 20,
      "gated": false,
      "within": null,
      "note": "",
      "dispute_note": "The other half of the same contradiction — see KPI. The printed plates' 2.82 mA through the 10 kΩ alone gives 28.2 V, which fits the printed +27 V only if the 10 kΩ returns to ground; through the drawn foot (56 kΩ ∥ 5 kΩ = 4.6 kΩ) the same current puts the junction at 41.2 V."
    },
    {
      "node": "PRES",
      "chart": null,
      "sim": 12.531,
      "disputed": false,
      "dev_pct": null,
      "tol_pct": 5,
      "gated": false,
      "within": null,
      "note": "informational — the tail's foot, where the 10 kΩ, the 56 kΩ feedback resistor, the presence pot's track and the V3B grid's 0.1 µF meet; the drawing prints no figure here",
      "dispute_note": ""
    },
    {
      "node": "GA1",
      "chart": -41,
      "sim": -41,
      "disputed": false,
      "dev_pct": 0,
      "tol_pct": 8,
      "gated": true,
      "within": true,
      "note": "fixed bias via the 220 kΩ leaks from the −41 V supply",
      "dispute_note": ""
    },
    {
      "node": "SA1",
      "chart": null,
      "sim": 394.239,
      "disputed": false,
      "dev_pct": null,
      "tol_pct": 5,
      "gated": false,
      "within": null,
      "note": "informational — 5881 screen after its 470 Ω; the sheet prints no screen figure",
      "dispute_note": ""
    }
  ],
  "checks": [
    {
      "id": "dc",
      "title": "DC operating point",
      "status": "Within target",
      "summary": "12 reference nodes are within tolerance. The circuit remains a draft awaiting maintainer review.",
      "details": [
        "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": "Not checked",
      "summary": "No published check result is available.",
      "details": [],
      "tone": "neutral"
    },
    {
      "id": "board",
      "title": "Board against DC model",
      "status": "Not checked",
      "summary": "No published check result is available.",
      "details": [],
      "tone": "neutral"
    },
    {
      "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.",
        "5 sheet-only parts are explicitly excluded: C11, C11b, C12, C13, RKCF. 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": "4 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": [],
  "sourceDirectory": "https://github.com/TheAnalogMaker/circuit-codex/tree/195289eab0b0e41029bffd6e34b65f01a84e553b/amps/5f8a"
}