{
  "format": "circuit-codex-reference",
  "version": 1,
  "id": "m1987",
  "url": "https://circuitcodex.com/amps/m1987/",
  "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": "m1987",
    "name_style": "Plexi lead 50-style",
    "family": "british",
    "era": {
      "start": 1967,
      "end": 1981
    },
    "wattage": 50,
    "tubes": [
      "ECC83",
      "ECC83",
      "ECC83",
      "EL34",
      "EL34"
    ],
    "topology": {
      "rectifier": {
        "kind": "solid-state",
        "type": "silicon full-wave"
      },
      "bias": "fixed",
      "phase_inverter": "long-tailed-pair",
      "tone_stack": "cathode-follower-fmv"
    },
    "lineage": {
      "derived_from": [
        "jtm45"
      ],
      "influenced": []
    },
    "conventions": {
      "designators": "functional"
    },
    "sources": [
      {
        "desc": "Marshall model 1987 factory drawing — Unicord drawing 70-19-11, dated July 1970 (Unicord Inc., Westbury NY, Marshall's US importer). Title block reads 'MARSHALL 1987'; complement 3x ECC83 (V1/V2/V3) + 2x EL34 (V4/V5), silicon full-wave rectifier (NO rectifier valve). Every component value read directly from the published drawing: dual-channel input (68k/68k stoppers, 1M leaks, 100k plates; V1A cathode 820R/320uF, V1B cathode 2.7k/0.68uF); V2A second stage (100k plate, 820R/0.68uF cathode, drawing annotates the 820R as '(1k)' variant); V2B DC-coupled cathode follower (100k load); FMV tone stack (33k slope, 500pF/250k treble, 0.022/1M bass, 0.022/25k mid); long-tailed-pair PI (100k/82k plates, 470R + 10k tail, 1M leaks to the junction, 47pF); EL34 pair fixed-biased through 220k grid leaks off a diode/220k/15k/25k/8uF bias supply; power 490-ish HT, choke, 50uF/80uF reservoir, two series 10k/1W droppers to the PI, then 10k/1W to V2 and 10k/1W to V1; 47k (100k variant) feedback from the 8-ohm tap to the presence/tail-foot node, universal mains taps 110/120/200/225/245. The drawing prints NO valve-voltage chart. Not reproduced here; archived at Dr. Tube.",
        "url": "https://www.drtube.com/schematics/marshall/1987u.gif"
      },
      {
        "desc": "Marshall 'Model 1987 (plexi)' schematic redrawn by Joe Piazza, 1/15/97 — cross-reference. Independently confirms the topology and the unusual V1B 2.7k cathode. It differs from the factory drawing on the V1B/V2A cathode-bypass caps, printing them as 68uF where the Unicord drawing reads 0.68uF; the factory value is used here. (The bypass-cap value is open at DC and does not affect the operating point either way.)",
        "url": "https://www.drtube.com/schematics/marshall/1987pljp.gif"
      },
      {
        "desc": "Mullard/Philips EL34 data sheet, January 1969 (A.F. Output Pentode) — anchor for the CC0 EL34 tube model and the octal basing (socket 5903/13): Va=250 V, Vg2=250 V, Vg1=-13.5 V -> Ia=100 mA, Ig2=14.9 mA, gm=12.5 mA/V, mu(g1-g2)=11",
        "url": "https://frank.pocnet.net/sheets/010/e/EL34.pdf"
      }
    ],
    "verification": {
      "status": "draft"
    },
    "added": "2026-07-19T00:00:00.000Z",
    "contributors": [
      "TheAnalogMaker"
    ]
  },
  "parts": {
    "notes": "Cathode-bypass and coupling capacitor VALUES are open at DC and do not enter the operating-point netlist; they are listed for completeness. The Joe Piazza redraw prints the V1B/V2A bypass caps as 68 µF where this factory drawing reads 0.68 µF — the factory value is used (see the sources on this page).",
    "items": [
      {
        "ref": "R1s",
        "part": "Carbon comp resistor",
        "value": "68 kΩ · ½ W",
        "role": "Channel I high-treble input grid stopper"
      },
      {
        "ref": "R2s",
        "part": "Carbon comp resistor",
        "value": "68 kΩ · ½ W",
        "role": "Channel I normal input grid stopper"
      },
      {
        "ref": "R3s",
        "part": "Carbon comp resistor",
        "value": "68 kΩ · ½ W",
        "role": "Channel II high input grid stopper"
      },
      {
        "ref": "R4s",
        "part": "Carbon comp resistor",
        "value": "68 kΩ · ½ W",
        "role": "Channel II low input grid stopper"
      },
      {
        "ref": "RG1",
        "part": "Carbon comp resistor",
        "value": "1 MΩ · ½ W",
        "role": "Channel I input grid leak"
      },
      {
        "ref": "RG2",
        "part": "Carbon comp resistor",
        "value": "1 MΩ · ½ W",
        "role": "Channel II input grid leak"
      },
      {
        "ref": "RL1",
        "part": "Carbon comp resistor",
        "value": "100 kΩ · ½ W",
        "role": "V1A plate load (channel I)"
      },
      {
        "ref": "RL2",
        "part": "Carbon comp resistor",
        "value": "100 kΩ · ½ W",
        "role": "V1B plate load (channel II)"
      },
      {
        "ref": "RK1",
        "part": "Carbon comp resistor",
        "value": "820 Ω · ½ W",
        "role": "V1A cathode bias (channel I)"
      },
      {
        "ref": "C1",
        "part": "Electrolytic capacitor",
        "value": "320 µF · 6 V",
        "role": "V1A cathode bypass"
      },
      {
        "ref": "RK2",
        "part": "Carbon comp resistor",
        "value": "2.7 kΩ · ½ W",
        "role": "V1B cathode bias (channel II — the colder channel)"
      },
      {
        "ref": "C2",
        "part": "Film capacitor",
        "value": "0.68 µF",
        "role": "V1B cathode bypass (partial)"
      },
      {
        "ref": "C3",
        "part": "Coupling capacitor",
        "value": "0.022 µF · 400 V",
        "role": "V1A → channel I volume"
      },
      {
        "ref": "C4",
        "part": "Coupling capacitor",
        "value": "0.0022 µF · 400 V",
        "role": "V1B → channel II volume"
      },
      {
        "ref": "VR1",
        "part": "Audio-taper potentiometer",
        "value": "1 MΩ",
        "role": "Channel I (high-treble) volume"
      },
      {
        "ref": "VR2",
        "part": "Audio-taper potentiometer",
        "value": "1 MΩ",
        "role": "Channel II (normal) volume"
      },
      {
        "ref": "C5",
        "part": "Film capacitor",
        "value": "0.005 µF",
        "role": "Channel I bright/treble-bleed cap"
      },
      {
        "ref": "C6",
        "part": "Mica capacitor",
        "value": "500 pF",
        "role": "Channel II bright cap"
      },
      {
        "ref": "RB1",
        "part": "Carbon comp resistor",
        "value": "470 kΩ · ½ W",
        "role": "Channel I bright-network resistor"
      },
      {
        "ref": "RB2",
        "part": "Carbon comp resistor",
        "value": "470 kΩ · ½ W",
        "role": "Channel II bright-network resistor"
      },
      {
        "ref": "RM1",
        "part": "Carbon comp resistor",
        "value": "470 kΩ · ½ W",
        "role": "Channel I mixing resistor into V2A grid"
      },
      {
        "ref": "RM2",
        "part": "Carbon comp resistor",
        "value": "470 kΩ · ½ W",
        "role": "Channel II mixing resistor into V2A grid"
      },
      {
        "ref": "RL3",
        "part": "Carbon comp resistor",
        "value": "100 kΩ · ½ W",
        "role": "V2A plate load (second stage)"
      },
      {
        "ref": "RK3",
        "part": "Carbon comp resistor",
        "value": "820 Ω · ½ W",
        "role": "V2A cathode bias (drawing annotates a 1 kΩ variant)"
      },
      {
        "ref": "C7",
        "part": "Film capacitor",
        "value": "0.68 µF",
        "role": "V2A cathode bypass (partial)"
      },
      {
        "ref": "RKCF",
        "part": "Carbon comp resistor",
        "value": "100 kΩ · ½ W",
        "role": "V2B cathode-follower load"
      },
      {
        "ref": "RSL",
        "part": "Carbon comp resistor",
        "value": "33 kΩ · ½ W",
        "role": "Tone-stack slope resistor"
      },
      {
        "ref": "C8",
        "part": "Mica capacitor",
        "value": "500 pF",
        "role": "Tone stack — treble"
      },
      {
        "ref": "VR3",
        "part": "Potentiometer",
        "value": "250 kΩ",
        "role": "Treble"
      },
      {
        "ref": "C9",
        "part": "Film capacitor",
        "value": "0.022 µF · 400 V",
        "role": "Tone stack — bass"
      },
      {
        "ref": "VR4",
        "part": "Audio-taper potentiometer",
        "value": "1 MΩ",
        "role": "Bass"
      },
      {
        "ref": "C10",
        "part": "Film capacitor",
        "value": "0.022 µF · 400 V",
        "role": "Tone stack — middle"
      },
      {
        "ref": "VR5",
        "part": "Linear potentiometer",
        "value": "25 kΩ",
        "role": "Middle"
      },
      {
        "ref": "C11",
        "part": "Coupling capacitor",
        "value": "0.022 µF · 400 V",
        "role": "Tone stack → 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": "100 kΩ · ½ W",
        "role": "PI plate load (V3A)"
      },
      {
        "ref": "RLB",
        "part": "Carbon comp resistor",
        "value": "82 kΩ · ½ W",
        "role": "PI plate load (V3B)"
      },
      {
        "ref": "RTAIL",
        "part": "Carbon comp resistor",
        "value": "470 Ω · ½ W",
        "role": "PI tail (shared cathode → junction)"
      },
      {
        "ref": "RT2",
        "part": "Carbon comp resistor",
        "value": "10 kΩ · ½ W",
        "role": "PI tail (junction → presence/feedback node)"
      },
      {
        "ref": "C12",
        "part": "Mica capacitor",
        "value": "47 pF",
        "role": "PI plate-to-plate / phase compensation"
      },
      {
        "ref": "C13",
        "part": "Coupling capacitor",
        "value": "0.022 µF · 400 V",
        "role": "PI → V4 grid"
      },
      {
        "ref": "C14",
        "part": "Coupling capacitor",
        "value": "0.022 µF · 400 V",
        "role": "PI → V5 grid"
      },
      {
        "ref": "RGL1",
        "part": "Carbon comp resistor",
        "value": "220 kΩ · ½ W",
        "role": "V4 grid leak, from the bias line"
      },
      {
        "ref": "RGL2",
        "part": "Carbon comp resistor",
        "value": "220 kΩ · ½ W",
        "role": "V5 grid leak, from the bias line"
      },
      {
        "ref": "D1",
        "part": "Rectifier (bias)",
        "value": "silicon diode",
        "role": "Bias-supply rectifier"
      },
      {
        "ref": "RBA",
        "part": "Carbon comp resistor",
        "value": "220 kΩ · ½ W",
        "role": "Bias-supply series resistor, HT winding end → diode"
      },
      {
        "ref": "RBB",
        "part": "Carbon comp resistor",
        "value": "15 kΩ · ½ W",
        "role": "Bias-supply series resistor"
      },
      {
        "ref": "VR6",
        "part": "Trim potentiometer",
        "value": "25 kΩ",
        "role": "Bias adjust"
      },
      {
        "ref": "RBC",
        "part": "Carbon comp resistor",
        "value": "47 kΩ · ½ W",
        "role": "Bias-supply resistor"
      },
      {
        "ref": "C15",
        "part": "Electrolytic capacitor",
        "value": "8 µF",
        "role": "Bias-supply filter"
      },
      {
        "ref": "C16",
        "part": "Electrolytic capacitor",
        "value": "8 µF",
        "role": "Bias-supply filter"
      },
      {
        "ref": "RD1",
        "part": "Power resistor",
        "value": "20 kΩ · 2 W",
        "role": "Rail dropper B+2 (screens) → B+3 (phase inverter), representing the drawing's two series 10 kΩ · 1 W resistors"
      },
      {
        "ref": "RD2",
        "part": "Power resistor",
        "value": "10 kΩ · 1 W",
        "role": "Rail dropper B+3 (phase inverter) → B+4 (second stage / cathode follower)"
      },
      {
        "ref": "RD3",
        "part": "Power resistor",
        "value": "10 kΩ · 1 W",
        "role": "Rail dropper B+4 (second stage) → B+5 (input stage)"
      },
      {
        "ref": "L1",
        "part": "Filter choke",
        "value": "inductance not printed",
        "role": "Reservoir → screen-supply choke, drawn unlettered on the drawing"
      },
      {
        "ref": "C17",
        "part": "Electrolytic capacitor",
        "value": "50 µF · 500 V",
        "role": "Reservoir filter (B+1)"
      },
      {
        "ref": "C18",
        "part": "Electrolytic capacitor",
        "value": "80 µF · 500 V",
        "role": "Reservoir filter (B+1)"
      },
      {
        "ref": "C19",
        "part": "Electrolytic capacitor",
        "value": "50 µF · 500 V",
        "role": "Screen-node filter"
      },
      {
        "ref": "C20",
        "part": "Electrolytic capacitor",
        "value": "50 µF · 500 V",
        "role": "Phase-inverter-supply filter"
      },
      {
        "ref": "C21",
        "part": "Electrolytic capacitor",
        "value": "50 µF · 350 V",
        "role": "Second-stage-supply filter"
      },
      {
        "ref": "C22",
        "part": "Electrolytic capacitor",
        "value": "50 µF · 350 V",
        "role": "Input-stage-supply filter"
      },
      {
        "ref": "D2",
        "part": "Rectifier diode",
        "value": "silicon",
        "role": "HT full-wave rectifier (upper)"
      },
      {
        "ref": "D3",
        "part": "Rectifier diode",
        "value": "silicon",
        "role": "HT full-wave rectifier (lower)"
      },
      {
        "ref": "C23",
        "part": "Film capacitor",
        "value": "0.22 µF",
        "role": "HT-winding snubber across the upper half of the HT secondary (end to the grounded centre tap). The drawing letters it “22”; read as 0.22 µF, the value the model 1959 sheet by the same drawer letters “.22”"
      },
      {
        "ref": "C24",
        "part": "Film capacitor",
        "value": "0.22 µF",
        "role": "HT-winding snubber across the lower half of the HT secondary (end to the grounded centre tap). The drawing letters it “22”; read as 0.22 µF, the value the model 1959 sheet by the same drawer letters “.22”"
      },
      {
        "ref": "V1",
        "part": "Preamp tube",
        "value": "ECC83 (12AX7)",
        "role": "Input valve — both channels (V1A/V1B)"
      },
      {
        "ref": "V2",
        "part": "Preamp tube",
        "value": "ECC83 (12AX7)",
        "role": "Second stage + cathode follower (V2A/V2B)"
      },
      {
        "ref": "V3",
        "part": "Preamp tube",
        "value": "ECC83 (12AX7)",
        "role": "Long-tailed-pair phase inverter (V3A/V3B)"
      },
      {
        "ref": "V4",
        "part": "Power tube",
        "value": "EL34",
        "role": "Push-pull output (upper)"
      },
      {
        "ref": "V5",
        "part": "Power tube",
        "value": "EL34",
        "role": "Push-pull output (lower)"
      },
      {
        "ref": "T1",
        "part": "Output transformer",
        "value": "Push-pull EL34 primary, 16/8/4 Ω secondary",
        "role": "Output transformer"
      },
      {
        "ref": "—",
        "part": "Power transformer",
        "value": "Universal primary 110/120/200/225/245 V · HT + 6.3 V heaters",
        "role": "Mains/HT transformer"
      },
      {
        "ref": "—",
        "part": "Fuse",
        "value": "2 A",
        "role": "Mains fuse (annotation)"
      },
      {
        "ref": "—",
        "part": "Fuse",
        "value": "½ A",
        "role": "HT fuse (annotation)"
      },
      {
        "ref": "—",
        "part": "Standby switch",
        "value": "SPST",
        "role": "HT standby (annotation)"
      },
      {
        "ref": "—",
        "part": "Pilot lamp",
        "value": "6.3 V",
        "role": "Panel pilot lamp (annotation)"
      },
      {
        "ref": "RNFB",
        "part": "Carbon comp resistor",
        "value": "47 kΩ · ½ W",
        "role": "Negative feedback from the 8 Ω tap to the tail foot; drawing annotates a 100 kΩ variant"
      },
      {
        "ref": "VR7",
        "part": "Linear potentiometer",
        "value": "5 kΩ",
        "role": "Presence track from tail foot to ground"
      },
      {
        "ref": "C25",
        "part": "Film capacitor",
        "value": "0.1 µF",
        "role": "V3B grid AC-coupled to the presence/feedback node"
      },
      {
        "ref": "C26",
        "part": "Film capacitor",
        "value": "0.1 µF",
        "role": "Presence wiper to ground"
      }
    ]
  },
  "publishedVoltages": {
    "source": "Marshall model 1987 factory drawing (Unicord 70-19-11, July 1970) — component values only; the drawing prints NO valve-voltage chart. Values below are simulated from the redrawn netlist, not read from any chart.",
    "nodes": {
      "BP2": {
        "chart": null,
        "note": "EL34 screen-grid supply node, after the filter choke (~B+1)"
      },
      "BP3": {
        "chart": null,
        "note": "phase-inverter supply node"
      },
      "BP4": {
        "chart": null,
        "note": "second-stage / cathode-follower supply node, after the 47 kΩ dropper"
      },
      "BP5": {
        "chart": null,
        "note": "input-stage supply node, after the 10 kΩ dropper"
      },
      "P1A": {
        "chart": null,
        "note": "V1A plate — channel I (high-treble) input, 100 kΩ load, 820 Ω cathode"
      },
      "K1A": {
        "chart": null,
        "note": "V1A cathode (820 Ω; 320 µF bypass)"
      },
      "P1B": {
        "chart": null,
        "note": "V1B plate — channel II (normal) input, 100 kΩ load, 2.7 kΩ cathode"
      },
      "K1B": {
        "chart": null,
        "note": "V1B cathode (2.7 kΩ; 0.68 µF bypass) — the colder-biased channel"
      },
      "P2A": {
        "chart": null,
        "note": "V2A plate — second gain stage (100 kΩ load), DC-coupled to the cathode follower"
      },
      "K2A": {
        "chart": null,
        "note": "V2A cathode (820 Ω; 0.68 µF bypass)"
      },
      "KCF": {
        "chart": null,
        "note": "V2B cathode follower output (100 kΩ load) feeding the TMB tone stack"
      },
      "PPIA": {
        "chart": null,
        "note": "phase-inverter plate, 100 kΩ side (V3A)"
      },
      "PPIB": {
        "chart": null,
        "note": "phase-inverter plate, 82 kΩ side (V3B)"
      },
      "KPI": {
        "chart": null,
        "note": "phase-inverter shared cathode over the 470 Ω / 10 kΩ tail"
      }
    }
  },
  "operatingPoint": [
    {
      "node": "BP2",
      "chart": null,
      "sim": 489.628,
      "disputed": false,
      "dev_pct": null,
      "tol_pct": 5,
      "gated": false,
      "within": null,
      "note": "EL34 screen-grid supply node, after the filter choke (~B+1)",
      "dispute_note": ""
    },
    {
      "node": "BP3",
      "chart": null,
      "sim": 340.658,
      "disputed": false,
      "dev_pct": null,
      "tol_pct": 5,
      "gated": false,
      "within": null,
      "note": "phase-inverter supply node",
      "dispute_note": ""
    },
    {
      "node": "BP4",
      "chart": null,
      "sim": 292.439,
      "disputed": false,
      "dev_pct": null,
      "tol_pct": 5,
      "gated": false,
      "within": null,
      "note": "second-stage / cathode-follower supply node, after the 47 kΩ dropper",
      "dispute_note": ""
    },
    {
      "node": "BP5",
      "chart": null,
      "sim": 273.5,
      "disputed": false,
      "dev_pct": null,
      "tol_pct": 5,
      "gated": false,
      "within": null,
      "note": "input-stage supply node, after the 10 kΩ dropper",
      "dispute_note": ""
    },
    {
      "node": "P1A",
      "chart": null,
      "sim": 153.628,
      "disputed": false,
      "dev_pct": null,
      "tol_pct": 5,
      "gated": false,
      "within": null,
      "note": "V1A plate — channel I (high-treble) input, 100 kΩ load, 820 Ω cathode",
      "dispute_note": ""
    },
    {
      "node": "K1A",
      "chart": null,
      "sim": 0.983,
      "disputed": false,
      "dev_pct": null,
      "tol_pct": 5,
      "gated": false,
      "within": null,
      "note": "V1A cathode (820 Ω; 320 µF bypass)",
      "dispute_note": ""
    },
    {
      "node": "P1B",
      "chart": null,
      "sim": 203.978,
      "disputed": false,
      "dev_pct": null,
      "tol_pct": 5,
      "gated": false,
      "within": null,
      "note": "V1B plate — channel II (normal) input, 100 kΩ load, 2.7 kΩ cathode",
      "dispute_note": ""
    },
    {
      "node": "K1B",
      "chart": null,
      "sim": 1.877,
      "disputed": false,
      "dev_pct": null,
      "tol_pct": 5,
      "gated": false,
      "within": null,
      "note": "V1B cathode (2.7 kΩ; 0.68 µF bypass) — the colder-biased channel",
      "dispute_note": ""
    },
    {
      "node": "P2A",
      "chart": null,
      "sim": 164.505,
      "disputed": false,
      "dev_pct": null,
      "tol_pct": 5,
      "gated": false,
      "within": null,
      "note": "V2A plate — second gain stage (100 kΩ load), DC-coupled to the cathode follower",
      "dispute_note": ""
    },
    {
      "node": "K2A",
      "chart": null,
      "sim": 1.049,
      "disputed": false,
      "dev_pct": null,
      "tol_pct": 5,
      "gated": false,
      "within": null,
      "note": "V2A cathode (820 Ω; 0.68 µF bypass)",
      "dispute_note": ""
    },
    {
      "node": "KCF",
      "chart": null,
      "sim": 164.86,
      "disputed": false,
      "dev_pct": null,
      "tol_pct": 5,
      "gated": false,
      "within": null,
      "note": "V2B cathode follower output (100 kΩ load) feeding the TMB tone stack",
      "dispute_note": ""
    },
    {
      "node": "PPIA",
      "chart": null,
      "sim": 217.179,
      "disputed": false,
      "dev_pct": null,
      "tol_pct": 5,
      "gated": false,
      "within": null,
      "note": "phase-inverter plate, 100 kΩ side (V3A)",
      "dispute_note": ""
    },
    {
      "node": "PPIB",
      "chart": null,
      "sim": 226.528,
      "disputed": false,
      "dev_pct": null,
      "tol_pct": 5,
      "gated": false,
      "within": null,
      "note": "phase-inverter plate, 82 kΩ side (V3B)",
      "dispute_note": ""
    },
    {
      "node": "KPI",
      "chart": null,
      "sim": 39.371,
      "disputed": false,
      "dev_pct": null,
      "tol_pct": 5,
      "gated": false,
      "within": null,
      "note": "phase-inverter shared cathode over the 470 Ω / 10 kΩ tail",
      "dispute_note": ""
    }
  ],
  "checks": [
    {
      "id": "dc",
      "title": "DC operating point",
      "status": "Simulation only",
      "summary": "No undisputed reference voltages are available for a comparison.",
      "details": [
        "This compares simulated DC conditions with the cited reference. It does not test sound, physical construction or every part of the circuit."
      ],
      "tone": "neutral"
    },
    {
      "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.",
        "11 sheet-only parts are explicitly excluded: C26, C5, C6, R1s, R2s, R3s, R4s, RB1, RB2, 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, V2, V3.",
        "No Marshall board-layout sheet was located for the model 1987; this board is derived from the factory drawing, 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": "9 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/ebddc3fd2cf887dca010bbe60487d7391ea6c052/amps/m1987"
}