{
  "format": "circuit-codex-reference",
  "version": 1,
  "id": "jtm45",
  "url": "https://circuitcodex.com/amps/jtm45/",
  "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": "jtm45",
    "name_style": "British lead-style",
    "family": "british",
    "era": {
      "start": 1962,
      "end": 1966
    },
    "wattage": 45,
    "tubes": [
      "ECC83",
      "ECC83",
      "ECC83",
      "KT66",
      "KT66",
      "GZ34"
    ],
    "topology": {
      "rectifier": {
        "kind": "tube",
        "type": "GZ34"
      },
      "bias": "fixed",
      "phase_inverter": "long-tailed-pair",
      "tone_stack": "cathode-follower-fmv"
    },
    "lineage": {
      "derived_from": [
        "5f6a"
      ],
      "influenced": [
        "m1959",
        "m1987"
      ]
    },
    "conventions": {
      "designators": "functional"
    },
    "sources": [
      {
        "desc": "Marshall factory drawing 'Basic schematic for Marshall trem amps, types 1961, 1962, 1987/T' — every legible component value AND the printed valve-voltage chart read directly from the published schematic. Core (non-tremolo) head: 3x ECC83 + 2x KT66 + GZ34; four input jacks, a 68k stopper each, each channel's 1M leak at its jack-1 tip; input 100k plates (V1A's printed '1■0K' has an illegible middle digit; 100k kept because the chart's equal plates falsify 180k) / shared 820R+250uF cathode, V1B feeding the bright (100pF) volume and a 56pF across the bright 270k mixer; V3 cathode-follower TMB stack (56k slope, 270pF/.02/.02 (treble/bass/middle), 250k/1M/25k); long-tailed-pair PI (82k/100k plates, 470R+10k tail, 1M leaks to the junction, a plate-to-plate cap of illegible value); KT66 screens fed by one shared 1k 2W then 470R 1W each, the 0.1uF couplers straight onto the grids (no grid stoppers: the drawing's only 33K is in the tremolo network); fixed bias from the HT winding end through a series R of illegible value, a diode, an '8' filter, 16k and a grid-line node with an illegible shunt and an unvalued electrolytic; power 360-0-360 HT, GZ34 (.05 from its cathode to the return), standby, 32uF reservoir, 20H choke with the output-transformer centre tap AFTER it, 8.2k + 10k droppers. Rails +450/+440/+380/+310, KT66 plates 430; the grid-line bubble '10 5V' is disputed and the chart's KT66 grid cell is illegible, so the model's -50 V bias is assumed, not read. Not reproduced here; archived at Dr. Tube.",
        "url": "https://www.drtube.com/schematics/marshall/jtm45tr.gif"
      },
      {
        "desc": "GEC / M-O Valve Co. KT66 data sheet (Issue 4, April 1963) — anchor for the CC0 KT66 tube model: Va=250 V, Vg2=250 V, Vg1=-15 V -> Ia=85 mA, gm=7 mA/V; screen Ig2=2.5 mA at the Class AB1 push-pull tetrode point (Vg2=300, Vg1=-27); mu(g1-g2)=9.5 from the triode-connection gm.ra",
        "url": "https://frank.pocnet.net/sheets/084/k/KT66_GEC.pdf"
      }
    ],
    "verification": {
      "status": "verified",
      "date": "2026-07-18T00:00:00.000Z",
      "max_deviation_pct": 6.5
    },
    "contributors": [
      "TheAnalogMaker"
    ]
  },
  "parts": {
    "notes": "The factory drawing shows four input jacks, two per channel, each with its own 68 kΩ stopper (R1s/R3s Normal into V1A, R2s/R4s Bright into V1B), and hangs each channel's 1 MΩ leak from jack 1's tip (jack 1 = the jack carrying the leak, the lower jack of each pair on the drawing). This is the plain (non-tremolo) head: the factory drawing's V2 tremolo valve and its 2G374 transistor signal-shunt network are omitted, so the valve numbering follows the drawing (V1 input, V3 second stage + cathode follower, V4 phase inverter, V5/V6 KT66, V7 GZ34). The bright cap is annotated and listed without a designator.",
    "items": [
      {
        "ref": "R1s",
        "part": "Carbon comp resistor",
        "value": "68 kΩ · ½ W",
        "role": "Normal-channel grid stopper, jack 1 (V1A)"
      },
      {
        "ref": "R3s",
        "part": "Carbon comp resistor",
        "value": "68 kΩ · ½ W",
        "role": "Normal-channel grid stopper, jack 2 (V1A)"
      },
      {
        "ref": "R2s",
        "part": "Carbon comp resistor",
        "value": "68 kΩ · ½ W",
        "role": "Bright-channel grid stopper, jack 1 (V1B)"
      },
      {
        "ref": "R4s",
        "part": "Carbon comp resistor",
        "value": "68 kΩ · ½ W",
        "role": "Bright-channel grid stopper, jack 2 (V1B)"
      },
      {
        "ref": "RG1",
        "part": "Carbon comp resistor",
        "value": "1 MΩ · ½ W",
        "role": "Normal input grid leak (V1A), from jack 1's tip to ground"
      },
      {
        "ref": "RG2",
        "part": "Carbon comp resistor",
        "value": "1 MΩ · ½ W",
        "role": "Bright input grid leak (V1B), from jack 1's tip to ground"
      },
      {
        "ref": "RL1",
        "part": "Carbon comp resistor",
        "value": "100 kΩ · ½ W",
        "role": "V1A plate load. Printed '1■0K': the middle digit is a solid blob that is not legible (0 or 8). 100 kΩ is modelled because the chart's equal 220 V plates on a shared cathode falsify 180 kΩ; that is elimination, not a reading"
      },
      {
        "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 ECC83 input cathode bias"
      },
      {
        "ref": "C3",
        "part": "Electrolytic capacitor",
        "value": "250 µF · 6 V",
        "role": "Shared input cathode bypass"
      },
      {
        "ref": "C1",
        "part": "Coupling capacitor",
        "value": "0.02 µF · 400 V",
        "role": "V1A → normal volume"
      },
      {
        "ref": "C2",
        "part": "Coupling capacitor",
        "value": "0.02 µF · 400 V",
        "role": "V1B → bright volume"
      },
      {
        "ref": "VR1",
        "part": "Audio-taper potentiometer",
        "value": "1 MΩ",
        "role": "Normal volume (fed by V1A)"
      },
      {
        "ref": "VR2",
        "part": "Audio-taper potentiometer",
        "value": "1 MΩ",
        "role": "Bright volume, fed by V1B (100 pF bright cap across it)"
      },
      {
        "ref": "RM1",
        "part": "Carbon comp resistor",
        "value": "270 kΩ · ½ W",
        "role": "Normal-channel mixer"
      },
      {
        "ref": "RM2",
        "part": "Carbon comp resistor",
        "value": "270 kΩ · ½ W",
        "role": "Bright-channel mixer"
      },
      {
        "ref": "C19",
        "part": "Mica capacitor",
        "value": "56 pF",
        "role": "Across the bright-channel 270 kΩ mixer (RM2). Printed '56pF', the first glyph partly overdrawn by the capacitor's lead: value probable, not certain"
      },
      {
        "ref": "RL3",
        "part": "Carbon comp resistor",
        "value": "100 kΩ · ½ W",
        "role": "V3A plate load"
      },
      {
        "ref": "RK2",
        "part": "Carbon comp resistor",
        "value": "820 Ω · ½ W",
        "role": "V3A cathode bias"
      },
      {
        "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": "C4",
        "part": "Mica capacitor",
        "value": "270 pF",
        "role": "Tone stack — treble"
      },
      {
        "ref": "VR3",
        "part": "Potentiometer",
        "value": "250 kΩ",
        "role": "Treble"
      },
      {
        "ref": "C5",
        "part": "Film capacitor",
        "value": "0.02 µF · 400 V",
        "role": "Tone stack — bass"
      },
      {
        "ref": "VR4",
        "part": "Audio-taper potentiometer",
        "value": "1 MΩ",
        "role": "Bass"
      },
      {
        "ref": "C6",
        "part": "Film capacitor",
        "value": "0.02 µF · 400 V",
        "role": "Tone stack — middle"
      },
      {
        "ref": "VR5",
        "part": "Linear potentiometer",
        "value": "25 kΩ",
        "role": "Middle"
      },
      {
        "ref": "C7",
        "part": "Coupling capacitor",
        "value": "0.02 µF · 400 V",
        "role": "Tone stack → phase-inverter grid"
      },
      {
        "ref": "RGA",
        "part": "Carbon comp resistor",
        "value": "1 MΩ · ½ W",
        "role": "PI grid leak (V4A), returned to tail junction"
      },
      {
        "ref": "RGB",
        "part": "Carbon comp resistor",
        "value": "1 MΩ · ½ W",
        "role": "PI grid leak (V4B), returned to tail junction"
      },
      {
        "ref": "RLA",
        "part": "Carbon comp resistor",
        "value": "82 kΩ · ½ W",
        "role": "PI plate load (V4A)"
      },
      {
        "ref": "RLB",
        "part": "Carbon comp resistor",
        "value": "100 kΩ · ½ W",
        "role": "PI plate load (V4B)"
      },
      {
        "ref": "C20",
        "part": "Capacitor",
        "value": "value not legible",
        "role": "PI plate-to-plate capacitor, V4A plate to V4B plate. Drawn on the factory sheet; its value marks match no digit on the drawing, so no value is given. DC-open, so not in the DC model"
      },
      {
        "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 → foot)"
      },
      {
        "ref": "C8",
        "part": "Film capacitor",
        "value": "0.1 µF · 400 V",
        "role": "V4B grid AC-coupled to the presence/feedback node"
      },
      {
        "ref": "C9",
        "part": "Coupling capacitor",
        "value": "0.1 µF · 400 V",
        "role": "PI → V5 grid"
      },
      {
        "ref": "C10",
        "part": "Coupling capacitor",
        "value": "0.1 µF · 400 V",
        "role": "PI → V6 grid"
      },
      {
        "ref": "RGL1",
        "part": "Carbon comp resistor",
        "value": "220 kΩ · ½ W",
        "role": "V5 grid leak, from the bias line (node B)"
      },
      {
        "ref": "RGL2",
        "part": "Carbon comp resistor",
        "value": "220 kΩ · ½ W",
        "role": "V6 grid leak, from the bias line (node B)"
      },
      {
        "ref": "RS3",
        "part": "Carbon comp resistor",
        "value": "1 kΩ · 2 W",
        "role": "Shared screen feed, B+2 → the screen junction (one resistor for both KT66 screens)"
      },
      {
        "ref": "RS1",
        "part": "Carbon comp resistor",
        "value": "470 Ω · 1 W",
        "role": "V5 screen resistor, from the screen junction. Printed '470 1W' (probable)"
      },
      {
        "ref": "RS2",
        "part": "Carbon comp resistor",
        "value": "470 Ω · 1 W",
        "role": "V6 screen resistor, from the screen junction. Printed '?70 1W': the first digit is not legible; 470 is the only standard value of that form (670 and 870 are not), which is elimination, not a reading"
      },
      {
        "ref": "RD1",
        "part": "Power resistor",
        "value": "8.2 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": "20 H",
        "role": "B+1 → B+2 (output-transformer centre tap, screen feed, PI dropper)"
      },
      {
        "ref": "C11",
        "part": "Electrolytic capacitor",
        "value": "32 µF · 500 V",
        "role": "Reservoir filter, B+1 (the 450 V node after the standby switch)"
      },
      {
        "ref": "C12",
        "part": "Electrolytic capacitor",
        "value": "32 µF · 500 V",
        "role": "Filter, B+2 (the node the OT centre tap sits on). Its label is the same glyph pair as the reservoir's '32': value probable"
      },
      {
        "ref": "C13",
        "part": "Electrolytic capacitor",
        "value": "16 µF · 500 V",
        "role": "Filter, B+3"
      },
      {
        "ref": "C14",
        "part": "Electrolytic capacitor",
        "value": "16 µF · 450 V",
        "role": "Filter, B+4"
      },
      {
        "ref": "RB1",
        "part": "Carbon comp resistor",
        "value": "not legible",
        "role": "Bias supply series resistor, from the HT winding end it shares with a GZ34 anode to the diode. Printed '1■0K': the middle digit is a solid blob (5, 6 or 8); no value is claimed"
      },
      {
        "ref": "D1",
        "part": "Rectifier (bias)",
        "value": "not printed",
        "role": "Bias supply rectifier, cathode toward the series resistor (the drawing prints no type at the symbol; its '1N4007' note is about replacing the GZ34)"
      },
      {
        "ref": "C18",
        "part": "Electrolytic capacitor",
        "value": "8 µF",
        "role": "Bias filter at the diode node (node A), − at the node. Printed '8' (probable); no voltage rating printed"
      },
      {
        "ref": "RB3",
        "part": "Carbon comp resistor",
        "value": "16 kΩ · ½ W",
        "role": "Bias filter series resistor, node A → the grid-line node (node B). Printed '16K' (probable)"
      },
      {
        "ref": "RB2",
        "part": "Carbon comp resistor",
        "value": "not legible",
        "role": "Bias shunt, grid-line node (node B) → return. Printed '5■K': the second digit is overprinted by a wire; no value is claimed"
      },
      {
        "ref": "C16",
        "part": "Electrolytic capacitor",
        "value": "not printed",
        "role": "Bias filter on the grid-line node (node B), − at the node and + at the return as printed"
      },
      {
        "ref": "C15",
        "part": "Film capacitor",
        "value": "0.05 µF",
        "role": "HT bypass, GZ34 cathode → return, on the rectifier side of the standby switch (not a bias part)"
      },
      {
        "ref": "V1",
        "part": "Preamp tube",
        "value": "ECC83 (12AX7)",
        "role": "Both input stages (V1A/V1B)"
      },
      {
        "ref": "V3",
        "part": "Preamp tube",
        "value": "ECC83 (12AX7)",
        "role": "Second stage + cathode follower (V3A/V3B)"
      },
      {
        "ref": "V4",
        "part": "Preamp tube",
        "value": "ECC83 (12AX7)",
        "role": "Long-tailed-pair phase inverter (V4A/V4B)"
      },
      {
        "ref": "V5",
        "part": "Power tube",
        "value": "KT66",
        "role": "Push-pull output (upper)"
      },
      {
        "ref": "V6",
        "part": "Power tube",
        "value": "KT66",
        "role": "Push-pull output (lower)"
      },
      {
        "ref": "V7",
        "part": "Rectifier tube",
        "value": "GZ34",
        "role": "Full-wave rectifier (V7A/V7B)"
      },
      {
        "ref": "T3",
        "part": "Output transformer",
        "value": "Push-pull, KT66 primary",
        "role": "Push-pull output to the speaker; centre tap on B+2, after the choke"
      },
      {
        "ref": "—",
        "part": "Power transformer",
        "value": "360-0-360 V HT · 6.3 V heaters",
        "role": "HT + heaters + rectifier filament"
      },
      {
        "ref": "—",
        "part": "Mica capacitor",
        "value": "100 pF",
        "role": "Bright cap across VR2, the volume V1B feeds (annotation only on schematic)"
      },
      {
        "ref": "RNFB",
        "part": "Carbon comp resistor",
        "value": "27 kΩ · ½ W",
        "role": "Negative feedback, speaker → tail foot"
      },
      {
        "ref": "VR6",
        "part": "Linear potentiometer",
        "value": "5 kΩ",
        "role": "Presence track, tail foot → ground"
      },
      {
        "ref": "C17",
        "part": "Film capacitor",
        "value": "0.1 µF · 400 V",
        "role": "Presence wiper → ground"
      }
    ]
  },
  "publishedVoltages": {
    "source": "Marshall JTM45 factory drawing, printed chart: rails +450 (GZ34 cathode) / +440 (screens) / +380 (PI) / +310 (preamp); V1 plate 220, cathode 1.6; V3A plate 190, cathode 1.1; V3B (CF) plate 310, grid 190, cathode 190; V4 (PI) plates 250, cathodes 40, grids '+'; V5/V6 KT66 plate 430, screen 440; V7 GZ34 cathode 450; bias-line bubble '10 5V' (disputed, see NBIAS)",
    "nodes": {
      "BP2": {
        "chart": 440,
        "tol_pct": 8,
        "note": "node after the 20H choke (DCR estimated): the output-transformer centre tap, the shared 1 kΩ screen feed and the 8.2 kΩ dropper all land here, so the choke carries the KT66 plate current"
      },
      "BP3": {
        "chart": 380,
        "tol_pct": 8,
        "note": "PI supply node after the 8.2 kΩ dropper"
      },
      "BP4": {
        "chart": 310,
        "tol_pct": 8,
        "note": "preamp node after the 10 kΩ dropper"
      },
      "P1A": {
        "chart": 220,
        "tol_pct": 20,
        "note": "ECC83 input plate (bright)"
      },
      "P1B": {
        "chart": 220,
        "tol_pct": 20,
        "note": "ECC83 input plate (normal)"
      },
      "KA": {
        "chart": 1.6,
        "tol_pct": 20,
        "note": "shared ECC83 input cathode, 820 Ω"
      },
      "P3A": {
        "chart": 190,
        "tol_pct": 20,
        "note": "V3A plate = cathode-follower grid (direct-coupled)"
      },
      "K3A": {
        "chart": 1.1,
        "tol_pct": 20,
        "note": "V3A cathode, 820 Ω"
      },
      "KCF": {
        "chart": 190,
        "tol_pct": 20,
        "note": "cathode-follower output (chart V3 pin 8)"
      },
      "PPIA": {
        "chart": 250,
        "tol_pct": 20,
        "note": "PI plate, 82 kΩ side"
      },
      "PPIB": {
        "chart": 250,
        "tol_pct": 20,
        "note": "PI plate, 100 kΩ side"
      },
      "KPI": {
        "chart": 40,
        "tol_pct": 20,
        "note": "Shared phase-inverter cathode. The 10 kΩ tail ends at the presence/feedback junction; the 5 kΩ track and 27 kΩ feedback resistor provide parallel DC returns to ground."
      },
      "JPI": {
        "chart": null,
        "note": "tail junction; the drawing marks the PI grids only as '+' (qualitative)"
      },
      "S5": {
        "chart": null,
        "note": "informational — V5 screen, fed from B+2 through the shared 1 kΩ 2 W and its own 470 Ω 1 W (chart screen 440 V). The house KT66 model draws no screen current at the modelled bias, so it reads B+2"
      },
      "NBIAS": {
        "chart": -105,
        "tol_pct": 8,
        "disputed": true,
        "dispute_note": "The drawing circles '10 5V' on the grid-line node (the junction of the 16 kΩ, the shunt to ground, the unvalued electrolytic and both 220 kΩ leaks): no minus sign and no decimal point are printed, with a blank 6 px gap between the 0 and the 5. The sign is taken from the drawn electrolytic on that node (− at the node, + at the return). As −105 V it cannot be the quiescent grid bias: the KT66's μ(g1–g2) of 9.5 (GEC data sheet, meta.yaml) puts cutoff near −440/9.5 ≈ −46 V at the chart's 440 V screens, so −105 V is about 59 V past cutoff; the valves would pass no plate current and each plate would read the centre-tap node, yet the chart prints the plates at 430 V, 10 V below the 440 V node the centre tap sits on. Read as −10.5 V it fails the other way: the house model then pulls about 460 mA from the reservoir and B+2 sags to about 381 V against the printed 440 V. The chart's own KT66 pin-5 cell is unreadable. The model's −50 V is an assumed figure, not this reading, and nothing on the drawing gates it."
      }
    }
  },
  "operatingPoint": [
    {
      "node": "BP2",
      "chart": 440,
      "sim": 433.755,
      "disputed": false,
      "dev_pct": 1.4193181818181828,
      "tol_pct": 8,
      "gated": true,
      "within": true,
      "note": "node after the 20H choke (DCR estimated): the output-transformer centre tap, the shared 1 kΩ screen feed and the 8.2 kΩ dropper all land here, so the choke carries the KT66 plate current",
      "dispute_note": ""
    },
    {
      "node": "BP3",
      "chart": 380,
      "sim": 367.622,
      "disputed": false,
      "dev_pct": 3.2573684210526275,
      "tol_pct": 8,
      "gated": true,
      "within": true,
      "note": "PI supply node after the 8.2 kΩ dropper",
      "dispute_note": ""
    },
    {
      "node": "BP4",
      "chart": 310,
      "sim": 315.32,
      "disputed": false,
      "dev_pct": 1.7161290322580625,
      "tol_pct": 8,
      "gated": true,
      "within": true,
      "note": "preamp node after the 10 kΩ dropper",
      "dispute_note": ""
    },
    {
      "node": "P1A",
      "chart": 220,
      "sim": 211.671,
      "disputed": false,
      "dev_pct": 3.7859090909090947,
      "tol_pct": 20,
      "gated": true,
      "within": true,
      "note": "ECC83 input plate (bright)",
      "dispute_note": ""
    },
    {
      "node": "P1B",
      "chart": 220,
      "sim": 211.671,
      "disputed": false,
      "dev_pct": 3.7859090909090947,
      "tol_pct": 20,
      "gated": true,
      "within": true,
      "note": "ECC83 input plate (normal)",
      "dispute_note": ""
    },
    {
      "node": "KA",
      "chart": 1.6,
      "sim": 1.7,
      "disputed": false,
      "dev_pct": 6.249999999999992,
      "tol_pct": 20,
      "gated": true,
      "within": true,
      "note": "shared ECC83 input cathode, 820 Ω",
      "dispute_note": ""
    },
    {
      "node": "P3A",
      "chart": 190,
      "sim": 177.628,
      "disputed": false,
      "dev_pct": 6.511578947368428,
      "tol_pct": 20,
      "gated": true,
      "within": true,
      "note": "V3A plate = cathode-follower grid (direct-coupled)",
      "dispute_note": ""
    },
    {
      "node": "K3A",
      "chart": 1.1,
      "sim": 1.129,
      "disputed": false,
      "dev_pct": 2.6363636363636282,
      "tol_pct": 20,
      "gated": true,
      "within": true,
      "note": "V3A cathode, 820 Ω",
      "dispute_note": ""
    },
    {
      "node": "KCF",
      "chart": 190,
      "sim": 178.031,
      "disputed": false,
      "dev_pct": 6.299473684210523,
      "tol_pct": 20,
      "gated": true,
      "within": true,
      "note": "cathode-follower output (chart V3 pin 8)",
      "dispute_note": ""
    },
    {
      "node": "PPIA",
      "chart": 250,
      "sim": 244.338,
      "disputed": false,
      "dev_pct": 2.2648000000000024,
      "tol_pct": 20,
      "gated": true,
      "within": true,
      "note": "PI plate, 82 kΩ side",
      "dispute_note": ""
    },
    {
      "node": "PPIB",
      "chart": 250,
      "sim": 234.499,
      "disputed": false,
      "dev_pct": 6.200400000000002,
      "tol_pct": 20,
      "gated": true,
      "within": true,
      "note": "PI plate, 100 kΩ side",
      "dispute_note": ""
    },
    {
      "node": "KPI",
      "chart": 40,
      "sim": 41.638,
      "disputed": false,
      "dev_pct": 4.094999999999995,
      "tol_pct": 20,
      "gated": true,
      "within": true,
      "note": "Shared phase-inverter cathode. The 10 kΩ tail ends at the presence/feedback junction; the 5 kΩ track and 27 kΩ feedback resistor provide parallel DC returns to ground.",
      "dispute_note": ""
    },
    {
      "node": "JPI",
      "chart": null,
      "sim": 40.306,
      "disputed": false,
      "dev_pct": null,
      "tol_pct": 5,
      "gated": false,
      "within": null,
      "note": "tail junction; the drawing marks the PI grids only as '+' (qualitative)",
      "dispute_note": ""
    },
    {
      "node": "S5",
      "chart": null,
      "sim": 433.755,
      "disputed": false,
      "dev_pct": null,
      "tol_pct": 5,
      "gated": false,
      "within": null,
      "note": "informational — V5 screen, fed from B+2 through the shared 1 kΩ 2 W and its own 470 Ω 1 W (chart screen 440 V). The house KT66 model draws no screen current at the modelled bias, so it reads B+2",
      "dispute_note": ""
    },
    {
      "node": "NBIAS",
      "chart": -105,
      "sim": -50,
      "disputed": true,
      "dev_pct": 52.38095238095239,
      "tol_pct": 8,
      "gated": false,
      "within": null,
      "note": "",
      "dispute_note": "The drawing circles '10 5V' on the grid-line node (the junction of the 16 kΩ, the shunt to ground, the unvalued electrolytic and both 220 kΩ leaks): no minus sign and no decimal point are printed, with a blank 6 px gap between the 0 and the 5. The sign is taken from the drawn electrolytic on that node (− at the node, + at the return). As −105 V it cannot be the quiescent grid bias: the KT66's μ(g1–g2) of 9.5 (GEC data sheet, meta.yaml) puts cutoff near −440/9.5 ≈ −46 V at the chart's 440 V screens, so −105 V is about 59 V past cutoff; the valves would pass no plate current and each plate would read the centre-tap node, yet the chart prints the plates at 430 V, 10 V below the 440 V node the centre tap sits on. Read as −10.5 V it fails the other way: the house model then pulls about 460 mA from the reservoir and B+2 sags to about 381 V against the printed 440 V. The chart's own KT66 pin-5 cell is unreadable. The model's −50 V is an assumed figure, not this reading, and nothing on the drawing gates it."
    }
  ],
  "checks": [
    {
      "id": "dc",
      "title": "DC operating point",
      "status": "Verified",
      "summary": "12 reference nodes are within tolerance. Maintainer verification is recorded for 2026-07-18; 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.",
        "1 disputed node is excluded from the tolerance result; its 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.",
        "7 sheet-only parts are explicitly excluded: C17, R1s, R2s, R3s, R4s, RG1, RG2. 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, V3, V4.",
        "No Marshall board-layout sheet was located for the JTM45; this board is derived from the factory schematic, so no factory drawing can establish its heater legs.",
        "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": "7 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": "jtm45-added-caps-2026-10-03",
      "date": "2026-10-03",
      "amps": [
        "jtm45"
      ],
      "title": "JTM45 mixer and phase-inverter capacitors",
      "description": "Two capacitors the factory drawing shows are now included. A 56 pF capacitor (probable reading) bridges the bright channel's mixing resistor, and a capacitor of illegible value joins the two phase-inverter plates. Neither affects the DC operating point.",
      "commit": "70f6ff8ce22c720d893835f463fc964d3b6fbe2c",
      "url": "https://github.com/TheAnalogMaker/circuit-codex/commit/70f6ff8ce22c720d893835f463fc964d3b6fbe2c"
    },
    {
      "id": "jtm45-bias-2026-10-03",
      "date": "2026-10-03",
      "amps": [
        "jtm45"
      ],
      "title": "JTM45 bias supply as drawn",
      "description": "The bias supply follows the factory drawing. A series resistor and a diode feed an 8 µF filter, then a 16 kΩ resistor feeds the grid-line node, which has a resistor and a capacitor to ground. Two resistor values and one capacitor value are not legible or not printed, and are listed that way. The 0.05 µF capacitor sits at the rectifier, not in the bias supply. The drawing's only bias figure, printed \"10 5V\", cannot be the operating bias and is shown as disputed. The model's −50 V bias is an assumption, not a reading.",
      "commit": "268cd85f35cafd3dc59f183b6cf4ba4c3d8d0299",
      "url": "https://github.com/TheAnalogMaker/circuit-codex/commit/268cd85f35cafd3dc59f183b6cf4ba4c3d8d0299"
    },
    {
      "id": "jtm45-channels-2026-10-03",
      "date": "2026-10-03",
      "amps": [
        "jtm45"
      ],
      "title": "JTM45 bright and normal channels",
      "description": "The factory drawing feeds the bright volume, the one carrying the 100 pF capacitor, from V1B, and the plain volume from V1A. The channel names had been swapped; the input wiring is unchanged. The first input stage's printed plate load has an illegible middle digit, and 100 kΩ is kept because the printed chart rules out the alternative.",
      "commit": "b7993eeed3c94aba504032d9752d912b331c90ea",
      "url": "https://github.com/TheAnalogMaker/circuit-codex/commit/b7993eeed3c94aba504032d9752d912b331c90ea"
    },
    {
      "id": "jtm45-grid-stoppers-2026-10-03",
      "date": "2026-10-03",
      "amps": [
        "jtm45"
      ],
      "title": "JTM45 output grid stoppers removed",
      "description": "The factory drawing couples each phase-inverter output straight to its KT66 grid. The 33 kΩ grid stoppers we listed are not on the drawing and have been removed. No operating point changes.",
      "commit": "287a59150872348b5a9e86de5f0b2efca25cc93e",
      "url": "https://github.com/TheAnalogMaker/circuit-codex/commit/287a59150872348b5a9e86de5f0b2efca25cc93e"
    },
    {
      "id": "jtm45-ht-feed-2026-10-03",
      "date": "2026-10-03",
      "amps": [
        "jtm45"
      ],
      "title": "JTM45 output-transformer feed and screen supply",
      "description": "The output transformer's centre tap now connects after the filter choke, as the factory drawing shows, and the filter there is 32 µF. The output-valve screens are fed through one shared 1 kΩ resistor and then a 470 Ω resistor each, replacing a 1 kΩ resistor per screen. The supply rails move down and remain within the published chart tolerances.",
      "commit": "bd01bbbe96bed8efbdf04e43b8be0182f165b430",
      "url": "https://github.com/TheAnalogMaker/circuit-codex/commit/bd01bbbe96bed8efbdf04e43b8be0182f165b430"
    },
    {
      "id": "jtm45-input-jacks-2026-10-03",
      "date": "2026-10-03",
      "amps": [
        "jtm45"
      ],
      "title": "JTM45 input jacks and grid leaks",
      "description": "The factory drawing shows four input jacks, each with its own 68 kΩ stopper, and hangs each channel's 1 MΩ leak from its first jack's tip, on the jack side of the stopper. We showed one jack per channel and drew the leak on the grid side. Both are corrected, and no operating point changes.",
      "commit": "b726555635b8c348027837df3d1678af5c14d074",
      "url": "https://github.com/TheAnalogMaker/circuit-codex/commit/b726555635b8c348027837df3d1678af5c14d074"
    }
  ],
  "sourceDirectory": "https://github.com/TheAnalogMaker/circuit-codex/tree/ebddc3fd2cf887dca010bbe60487d7391ea6c052/amps/jtm45"
}