{
  "format": "circuit-codex-reference",
  "version": 1,
  "id": "m2204",
  "url": "https://circuitcodex.com/amps/m2204/",
  "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": "m2204",
    "name_style": "Master Volume lead 50-style",
    "family": "british",
    "era": {
      "start": 1977,
      "end": 1989
    },
    "wattage": 50,
    "tubes": [
      "ECC83",
      "ECC83",
      "ECC83",
      "EL34",
      "EL34"
    ],
    "topology": {
      "rectifier": {
        "kind": "solid-state",
        "type": "silicon bridge"
      },
      "bias": "fixed",
      "phase_inverter": "long-tailed-pair",
      "tone_stack": "cathode-follower-fmv"
    },
    "lineage": {
      "derived_from": [
        "m1987"
      ],
      "influenced": []
    },
    "conventions": {
      "designators": "sequential",
      "notation": "uk"
    },
    "sources": [
      {
        "desc": "Marshall model 2204 factory drawing, sheet 1 of 2 — title block reads '2204 STD / Preamp', MARSHALL, Jim Marshall Products Ltd., Bletchley, Milton Keynes, England; file 2204PRE.DGM; issue 4, dated 19-5-88, drawn CPV. Note block: 'PCB: JM80. V1,2: ECC83.' Every preamp value read directly from the published drawing: one channel with High (J1) and Low (J2) inputs, R3 68k stopper and R2 1M leak into V1a (R4 100k plate, R1 2k7 cathode with C1 0.68u bypass, C2 100p across the triode); V1a couples out through C3 0.022u into the preamp-volume network (R5 470k bridged by C4 470p, VR1 1M log with C5 1n0 across its upper section) and the wiper drives V1b — a CASCADED second stage, not a second channel (R7 100k plate, R6 10k cathode UNBYPASSED); V1b plate through C7 0.022u into an R10 470k / R11 470k divider with C8 470p across the series arm, into V2a (R12 100k plate, R9 820R cathode unbypassed); V2b DC-coupled cathode follower (R13 100k load); FMV tone stack (R15 33k slope, C10 470p / VR3 220k lin treble, C11 0.022u / VR5 1M log bass wired as a rheostat, C12 0.022u / VR4 22k lin middle, output taken from the treble wiper through the panel link 'R14'); VR2 1M log master volume; supply rail X decoupled by R8 10k 1W with a C21 50+50u dual can. The drawing prints NO valve-voltage chart. Not reproduced here; archived at Dr. Tube.",
        "url": "https://www.drtube.com/schematics/marshall/2204prem.gif"
      },
      {
        "desc": "Marshall model 2204 factory drawing, sheet 2 of 2 — title block reads '2204 STD / Output Stage & PSU', MARSHALL, Jim Marshall Products Ltd., Bletchley, Milton Keynes, England; file 2204PWR.DGM; issue 1 dated 19-5-88 and issue 2 dated 18-6-89, both drawn CPV. Every value read directly from the published drawing: V3 ECC83 long-tailed-pair phase inverter (R18 82k plate on the driven side, R21 100k on the other, R16 470R shared cathode, R17 1M and R19 1M grid leaks returned to the tail junction, C9 0.022u in from the master volume, C15 0.1u from the cold grid to the feedback node); R20 10k tail to a feedback node carrying R23 4k7 to ground, R22 100k from the output-transformer secondary, and VR6 22k presence through C17 0.1u; C14 and C16 0.022u couplers to the output grids with C18 47p across them, R24 220k and R25 220k grid leaks off a common bias node, R31 5k6 and R32 5k6 grid stoppers; V4/V5 EL34 pair, cathodes grounded (fixed bias), R33 1k5 and R34 1k5 screen resistors; bias supply D1 1N4007 / R30 220k / C20 10u raw, R27 15k to the bias node with R26 56k and RV1 22k lin adjust and C19 10u filter; power a 4 x 1N4007 bridge into a C23 50+50u reservoir, HT fuse T500mA, T3 choke, C22 50+50u, R29 10k 1W to the preamp rail X; output transformer 789-139 with 16/8/4 ohm taps, mains transformer 1202-324 with 240/220/120 V selection, R35 2k2 / R36 100R / R37 560R DI network. The drawing prints NO valve-voltage chart. Not reproduced here; archived at Dr. Tube.",
        "url": "https://www.drtube.com/schematics/marshall/2204pwrm.gif"
      },
      {
        "desc": "The same two 2204 STD sheets mirrored as a single two-page PDF by thetubestore — used to read the drawing at higher resolution than the GIF scans allow. Identical title blocks, issues and dates; not an independent draughting of the circuit.",
        "url": "https://www.thetubestore.com/lib/thetubestore/schematics/Marshall/Marshall-50W-2204S-Schematic.pdf"
      },
      {
        "desc": "Marshall specification sheet '2204 50W MASTER VOLUME LEAD AMP / 2104 50W MASTER VOLUME LEAD AMP', dated 11/81 — prints the tube complement (V1, V2, V3 ECC83/12AX7; output valves V4, V5 '6550 for USA (EL34, KT77 elsewhere)'), power output (in excess of 50 W RMS at clipping into 4, 8 or 16 ohms, 3 % average distortion), input sensitivity, tone-control ranges, and power-supply requirements (120/220/240 Vac, 175 W maximum, HT fuse T500mA). This is the source for the EL34 complement documented here being the non-US fitment.",
        "url": "https://www.drtube.com/schematics/marshall/2204specs.gif"
      },
      {
        "desc": "Marshall model 2204 factory drawing, title block '50W MASTER MODEL / MODEL NO. 2204', dated 11/11/76, drawn FJK, Jim Marshall Products Ltd. for Unicord Incorporated, 75 Frost Street, Westbury NY — the EARLIER revision, and a different circuit from the one documented here: its V1 is a two-channel PARALLEL input pair mixed through 100k resistors (an 820R/330u and a 2.7k/0.68u cathode, exactly the 1987 front end) rather than the cascaded V1a-to-V1b chain, and its legend reads 'V4-5 6550'. Cited to fix which revision this entry documents, and as the only Marshall-printed voltage figures found for any 2204 (400 V at the output plates, 87 V at the phase-inverter plates, 205 V and 150 V at V1, 39 V at the inverter cathode, -63 V bias) — figures that belong to that other revision at US mains and are therefore NOT used as a chart here.",
        "url": "https://www.drtube.com/schematics/marshall/2204u.gif"
      },
      {
        "desc": "Wikipedia, 'Marshall Amplification' — the late-1975 introduction of the Master Volume series with the 100 W 2203 followed by the 50 W 2204 in 1976; the change that connects the input stages in series rather than in parallel and repurposes the second channel volume as a master volume, reaching the 2204 in early 1977; and the late-1980 repackaging of the 2203 and 2204 as the JCM800 series",
        "url": "https://en.wikipedia.org/wiki/Marshall_Amplification"
      },
      {
        "desc": "Mullard/Philips EL34 data sheet, January 1969 (A.F. Output Pentode) — anchor for the CC0 EL34 tube model: 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": "2026-08-08T00:00:00.000Z",
    "contributors": [
      "TheAnalogMaker"
    ]
  },
  "parts": {
    "notes": "The drawing prints component values with no wattage or voltage rating except where noted (R8 and R29 are marked 1 W), so ratings are not asserted here. Cathode-bypass and coupling capacitor VALUES are open at DC and do not enter the operating-point netlist; they are listed for completeness. Designators C6, C13 and R28 appear nowhere on either 2204 STD sheet — the JM80 board these sheets document is shared with other models, and unused positions are simply absent from this drawing; they are not omitted here by oversight.",
    "items": [
      {
        "ref": "J1",
        "part": "Jack socket",
        "value": "¼ in mono",
        "role": "High-sensitivity input"
      },
      {
        "ref": "J2",
        "part": "Jack socket",
        "value": "¼ in mono",
        "role": "Low-sensitivity input"
      },
      {
        "ref": "R2",
        "part": "Carbon film resistor",
        "value": "1 MΩ",
        "role": "Input grid leak"
      },
      {
        "ref": "R3",
        "part": "Carbon film resistor",
        "value": "68 kΩ",
        "role": "Input grid stopper into V1a"
      },
      {
        "ref": "R4",
        "part": "Carbon film resistor",
        "value": "100 kΩ",
        "role": "V1a plate load"
      },
      {
        "ref": "R1",
        "part": "Carbon film resistor",
        "value": "2.7 kΩ",
        "role": "V1a cathode bias"
      },
      {
        "ref": "C1",
        "part": "Electrolytic capacitor",
        "value": "0.68 µF",
        "role": "V1a cathode bypass"
      },
      {
        "ref": "C2",
        "part": "Ceramic capacitor",
        "value": "100 pF",
        "role": "Across V1a, plate to cathode — high-frequency shunt"
      },
      {
        "ref": "C3",
        "part": "Coupling capacitor",
        "value": "0.022 µF",
        "role": "V1a plate → preamp-volume network"
      },
      {
        "ref": "R5",
        "part": "Carbon film resistor",
        "value": "470 kΩ",
        "role": "Series arm ahead of the preamp volume"
      },
      {
        "ref": "C4",
        "part": "Ceramic capacitor",
        "value": "470 pF",
        "role": "Bright cap across R5"
      },
      {
        "ref": "VR1",
        "part": "Logarithmic potentiometer",
        "value": "1 MΩ",
        "role": "Preamp volume"
      },
      {
        "ref": "C5",
        "part": "Film capacitor",
        "value": "0.001 µF",
        "role": "Bright cap across the preamp volume's upper section (drawn '1n0')"
      },
      {
        "ref": "R7",
        "part": "Carbon film resistor",
        "value": "100 kΩ",
        "role": "V1b plate load"
      },
      {
        "ref": "R6",
        "part": "Carbon film resistor",
        "value": "10 kΩ",
        "role": "V1b cathode bias — unbypassed"
      },
      {
        "ref": "R8",
        "part": "Power resistor",
        "value": "10 kΩ · 1 W",
        "role": "Rail dropper, preamp rail → input-stage rail"
      },
      {
        "ref": "C21",
        "part": "Electrolytic capacitor",
        "value": "50 µF + 50 µF",
        "role": "Preamp-rail and input-stage-rail filter, one section each side of R8"
      },
      {
        "ref": "C7",
        "part": "Coupling capacitor",
        "value": "0.022 µF",
        "role": "V1b plate → interstage divider"
      },
      {
        "ref": "R10",
        "part": "Carbon film resistor",
        "value": "470 kΩ",
        "role": "Interstage divider, series arm"
      },
      {
        "ref": "C8",
        "part": "Ceramic capacitor",
        "value": "470 pF",
        "role": "Bright cap across R10"
      },
      {
        "ref": "R11",
        "part": "Carbon film resistor",
        "value": "470 kΩ",
        "role": "Interstage divider, shunt arm — also V2a's grid return"
      },
      {
        "ref": "R12",
        "part": "Carbon film resistor",
        "value": "100 kΩ",
        "role": "V2a plate load"
      },
      {
        "ref": "R9",
        "part": "Carbon film resistor",
        "value": "820 Ω",
        "role": "V2a cathode bias — unbypassed"
      },
      {
        "ref": "R13",
        "part": "Carbon film resistor",
        "value": "100 kΩ",
        "role": "V2b cathode-follower load"
      },
      {
        "ref": "R15",
        "part": "Carbon film resistor",
        "value": "33 kΩ",
        "role": "Tone-stack slope resistor"
      },
      {
        "ref": "C10",
        "part": "Ceramic capacitor",
        "value": "470 pF",
        "role": "Tone stack — treble"
      },
      {
        "ref": "VR3",
        "part": "Linear potentiometer",
        "value": "220 kΩ",
        "role": "Treble"
      },
      {
        "ref": "C11",
        "part": "Film capacitor",
        "value": "0.022 µF",
        "role": "Tone stack — bass"
      },
      {
        "ref": "VR5",
        "part": "Logarithmic potentiometer",
        "value": "1 MΩ",
        "role": "Bass — wired as a rheostat, wiper strapped to the top"
      },
      {
        "ref": "C12",
        "part": "Film capacitor",
        "value": "0.022 µF",
        "role": "Tone stack — middle"
      },
      {
        "ref": "VR4",
        "part": "Linear potentiometer",
        "value": "22 kΩ",
        "role": "Middle"
      },
      {
        "ref": "R14",
        "part": "Wire link",
        "value": "wire link",
        "role": "Panel link from the treble wiper to the master volume, in the R14 position"
      },
      {
        "ref": "VR2",
        "part": "Logarithmic potentiometer",
        "value": "1 MΩ",
        "role": "Master volume"
      },
      {
        "ref": "C9",
        "part": "Coupling capacitor",
        "value": "0.022 µF",
        "role": "Master volume → V3a grid"
      },
      {
        "ref": "R17",
        "part": "Carbon film resistor",
        "value": "1 MΩ",
        "role": "PI grid leak (V3a), returned to the tail junction"
      },
      {
        "ref": "R19",
        "part": "Carbon film resistor",
        "value": "1 MΩ",
        "role": "PI grid leak (V3b), returned to the tail junction"
      },
      {
        "ref": "R18",
        "part": "Carbon film resistor",
        "value": "82 kΩ",
        "role": "PI plate load (V3a, the driven side)"
      },
      {
        "ref": "R21",
        "part": "Carbon film resistor",
        "value": "100 kΩ",
        "role": "PI plate load (V3b)"
      },
      {
        "ref": "R16",
        "part": "Carbon film resistor",
        "value": "470 Ω",
        "role": "PI shared cathode resistor"
      },
      {
        "ref": "R20",
        "part": "Carbon film resistor",
        "value": "10 kΩ",
        "role": "PI tail, junction → feedback node"
      },
      {
        "ref": "C15",
        "part": "Film capacitor",
        "value": "0.1 µF",
        "role": "AC-grounds V3b's grid to the feedback node"
      },
      {
        "ref": "R22",
        "part": "Carbon film resistor",
        "value": "100 kΩ",
        "role": "Negative feedback, output-transformer secondary → feedback node"
      },
      {
        "ref": "R23",
        "part": "Carbon film resistor",
        "value": "4.7 kΩ",
        "role": "Feedback node → ground"
      },
      {
        "ref": "C17",
        "part": "Film capacitor",
        "value": "0.1 µF",
        "role": "Presence cap, feedback node → presence pot"
      },
      {
        "ref": "VR6",
        "part": "Potentiometer",
        "value": "22 kΩ",
        "role": "Presence"
      },
      {
        "ref": "C14",
        "part": "Coupling capacitor",
        "value": "0.022 µF",
        "role": "PI (V3a) → V4 grid"
      },
      {
        "ref": "C16",
        "part": "Coupling capacitor",
        "value": "0.022 µF",
        "role": "PI (V3b) → V5 grid"
      },
      {
        "ref": "C18",
        "part": "Ceramic capacitor",
        "value": "47 pF",
        "role": "Phase compensation, across the two output grids"
      },
      {
        "ref": "R24",
        "part": "Carbon film resistor",
        "value": "220 kΩ",
        "role": "V4 grid leak, from the bias node"
      },
      {
        "ref": "R25",
        "part": "Carbon film resistor",
        "value": "220 kΩ",
        "role": "V5 grid leak, from the bias node"
      },
      {
        "ref": "R31",
        "part": "Carbon film resistor",
        "value": "5.6 kΩ",
        "role": "V4 grid stopper"
      },
      {
        "ref": "R32",
        "part": "Carbon film resistor",
        "value": "5.6 kΩ",
        "role": "V5 grid stopper"
      },
      {
        "ref": "R33",
        "part": "Carbon film resistor",
        "value": "1.5 kΩ",
        "role": "V4 screen-grid resistor"
      },
      {
        "ref": "R34",
        "part": "Carbon film resistor",
        "value": "1.5 kΩ",
        "role": "V5 screen-grid resistor"
      },
      {
        "ref": "D1",
        "part": "Rectifier diode",
        "value": "1N4007",
        "role": "Bias-supply rectifier"
      },
      {
        "ref": "R30",
        "part": "Carbon film resistor",
        "value": "220 kΩ",
        "role": "Bias-supply series resistor"
      },
      {
        "ref": "C20",
        "part": "Electrolytic capacitor",
        "value": "10 µF",
        "role": "Bias-supply reservoir"
      },
      {
        "ref": "R27",
        "part": "Carbon film resistor",
        "value": "15 kΩ",
        "role": "Bias-supply series resistor into the bias node"
      },
      {
        "ref": "R26",
        "part": "Carbon film resistor",
        "value": "56 kΩ",
        "role": "Bias divider, upper leg"
      },
      {
        "ref": "RV1",
        "part": "Trim potentiometer",
        "value": "22 kΩ",
        "role": "Bias adjust"
      },
      {
        "ref": "C19",
        "part": "Electrolytic capacitor",
        "value": "10 µF",
        "role": "Bias-node filter"
      },
      {
        "ref": "D2",
        "part": "Rectifier diode",
        "value": "1N4007",
        "role": "HT bridge rectifier"
      },
      {
        "ref": "D3",
        "part": "Rectifier diode",
        "value": "1N4007",
        "role": "HT bridge rectifier"
      },
      {
        "ref": "D4",
        "part": "Rectifier diode",
        "value": "1N4007",
        "role": "HT bridge rectifier"
      },
      {
        "ref": "D5",
        "part": "Rectifier diode",
        "value": "1N4007",
        "role": "HT bridge rectifier"
      },
      {
        "ref": "C23",
        "part": "Electrolytic capacitor",
        "value": "50 µF + 50 µF",
        "role": "HT reservoir"
      },
      {
        "ref": "F2",
        "part": "Fuse",
        "value": "T500 mA",
        "role": "HT fuse"
      },
      {
        "ref": "T3",
        "part": "Filter choke",
        "value": "choke (value not marked)",
        "role": "Reservoir → screen-supply choke"
      },
      {
        "ref": "C22",
        "part": "Electrolytic capacitor",
        "value": "50 µF + 50 µF",
        "role": "Screen-node filter after the choke — both sections of the can land on that node (unlike C21, whose sections straddle R8)"
      },
      {
        "ref": "R29",
        "part": "Power resistor",
        "value": "10 kΩ · 1 W",
        "role": "Rail dropper, screen node → preamp rail"
      },
      {
        "ref": "S2",
        "part": "Toggle switch",
        "value": "SPST",
        "role": "Standby"
      },
      {
        "ref": "T2",
        "part": "Output transformer",
        "value": "Marshall 789-139 · 16/8/4 Ω taps",
        "role": "Push-pull EL34 output transformer"
      },
      {
        "ref": "SEL2",
        "part": "Rotary switch",
        "value": "3-position",
        "role": "Speaker impedance selector"
      },
      {
        "ref": "J3",
        "part": "Jack socket",
        "value": "¼ in mono",
        "role": "Speaker output"
      },
      {
        "ref": "J4",
        "part": "Jack socket",
        "value": "¼ in mono",
        "role": "Speaker output"
      },
      {
        "ref": "R35",
        "part": "Carbon film resistor",
        "value": "2.2 kΩ",
        "role": "DI attenuator, series arm off the secondary"
      },
      {
        "ref": "R36",
        "part": "Carbon film resistor",
        "value": "100 Ω",
        "role": "DI attenuator, shunt arm"
      },
      {
        "ref": "R37",
        "part": "Carbon film resistor",
        "value": "560 Ω",
        "role": "DI output series resistor"
      },
      {
        "ref": "J5",
        "part": "Jack socket",
        "value": "¼ in mono",
        "role": "DI output"
      },
      {
        "ref": "T1",
        "part": "Power transformer",
        "value": "Marshall 1202-324 · 240/220/120 V primary · HT + 6.3 V heaters",
        "role": "Mains/HT transformer"
      },
      {
        "ref": "SEL1",
        "part": "Voltage selector",
        "value": "240/220/120 V",
        "role": "Mains primary selection"
      },
      {
        "ref": "F1",
        "part": "Fuse",
        "value": "T2 A",
        "role": "Mains fuse (T3 A on 120 V)"
      },
      {
        "ref": "S1",
        "part": "Toggle switch",
        "value": "DPST",
        "role": "Mains switch"
      },
      {
        "ref": "MS1",
        "part": "Mains inlet",
        "value": "N / E / L",
        "role": "Mains connector"
      },
      {
        "ref": "V1",
        "part": "Preamp tube",
        "value": "ECC83 (12AX7)",
        "role": "Input stage + cascaded second stage (V1a/V1b)"
      },
      {
        "ref": "V2",
        "part": "Preamp tube",
        "value": "ECC83 (12AX7)",
        "role": "Third gain 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)"
      }
    ]
  },
  "publishedVoltages": {
    "source": "Marshall model 2204 STD factory drawing, sheets 2204PRE.DGM (iss 4, 19-5-88) and 2204PWR.DGM (iss 2, 18-6-89) — 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 supply node, after the filter choke (the OT centre tap is taken ahead of it, at B+1)"
      },
      "BP3": {
        "chart": null,
        "note": "preamp rail X — phase-inverter plates, V2a plate load and V2b plate, after the R29 10 kΩ dropper"
      },
      "BP4": {
        "chart": null,
        "note": "input-stage rail — V1a and V1b plate loads, after the R8 10 kΩ dropper"
      },
      "P1A": {
        "chart": null,
        "note": "V1a plate — input stage, 100 kΩ load, 2.7 kΩ cathode"
      },
      "K1A": {
        "chart": null,
        "note": "V1a cathode (2.7 kΩ; 0.68 µF bypass)"
      },
      "P1B": {
        "chart": null,
        "note": "V1b plate — cascaded second stage, 100 kΩ load"
      },
      "K1B": {
        "chart": null,
        "note": "V1b cathode (10 kΩ, unbypassed) — the cold, gain-shaping stage the 2204 adds over the 1987"
      },
      "P2A": {
        "chart": null,
        "note": "V2a plate — third gain stage (100 kΩ load), DC-coupled to the cathode follower"
      },
      "K2A": {
        "chart": null,
        "note": "V2a cathode (820 Ω, unbypassed)"
      },
      "KCF": {
        "chart": null,
        "note": "V2b cathode follower output (100 kΩ load) feeding the TMB tone stack"
      },
      "PPIA": {
        "chart": null,
        "note": "phase-inverter plate, 82 kΩ side (V3a — the driven side, fed from the master volume)"
      },
      "PPIB": {
        "chart": null,
        "note": "phase-inverter plate, 100 kΩ side (V3b)"
      },
      "KPI": {
        "chart": null,
        "note": "phase-inverter shared cathode over the 470 Ω cathode resistor"
      },
      "JPI": {
        "chart": null,
        "note": "phase-inverter tail junction — both 1 MΩ grid leaks return here, above the 10 kΩ tail"
      },
      "NNFB": {
        "chart": null,
        "note": "negative-feedback node at the foot of the tail: 4.7 kΩ to ground, 100 kΩ back to the output-transformer secondary, presence leg capacitor-blocked"
      },
      "SG4": {
        "chart": null,
        "note": "V4 screen grid, through its 1.5 kΩ screen resistor (the corpus's EL34 fit draws no screen current at this bias, so the drop reads as zero — see the circuit story)"
      },
      "SG5": {
        "chart": null,
        "note": "V5 screen grid, through its 1.5 kΩ screen resistor"
      }
    }
  },
  "operatingPoint": [
    {
      "node": "BP2",
      "chart": null,
      "sim": 469.592,
      "disputed": false,
      "dev_pct": null,
      "tol_pct": 5,
      "gated": false,
      "within": null,
      "note": "EL34 screen supply node, after the filter choke (the OT centre tap is taken ahead of it, at B+1)",
      "dispute_note": ""
    },
    {
      "node": "BP3",
      "chart": null,
      "sim": 388.045,
      "disputed": false,
      "dev_pct": null,
      "tol_pct": 5,
      "gated": false,
      "within": null,
      "note": "preamp rail X — phase-inverter plates, V2a plate load and V2b plate, after the R29 10 kΩ dropper",
      "dispute_note": ""
    },
    {
      "node": "BP4",
      "chart": null,
      "sim": 375.182,
      "disputed": false,
      "dev_pct": null,
      "tol_pct": 5,
      "gated": false,
      "within": null,
      "note": "input-stage rail — V1a and V1b plate loads, after the R8 10 kΩ dropper",
      "dispute_note": ""
    },
    {
      "node": "P1A",
      "chart": null,
      "sim": 282.806,
      "disputed": false,
      "dev_pct": null,
      "tol_pct": 5,
      "gated": false,
      "within": null,
      "note": "V1a plate — input stage, 100 kΩ load, 2.7 kΩ cathode",
      "dispute_note": ""
    },
    {
      "node": "K1A",
      "chart": null,
      "sim": 2.494,
      "disputed": false,
      "dev_pct": null,
      "tol_pct": 5,
      "gated": false,
      "within": null,
      "note": "V1a cathode (2.7 kΩ; 0.68 µF bypass)",
      "dispute_note": ""
    },
    {
      "node": "P1B",
      "chart": null,
      "sim": 338.927,
      "disputed": false,
      "dev_pct": null,
      "tol_pct": 5,
      "gated": false,
      "within": null,
      "note": "V1b plate — cascaded second stage, 100 kΩ load",
      "dispute_note": ""
    },
    {
      "node": "K1B",
      "chart": null,
      "sim": 3.625,
      "disputed": false,
      "dev_pct": null,
      "tol_pct": 5,
      "gated": false,
      "within": null,
      "note": "V1b cathode (10 kΩ, unbypassed) — the cold, gain-shaping stage the 2204 adds over the 1987",
      "dispute_note": ""
    },
    {
      "node": "P2A",
      "chart": null,
      "sim": 219.106,
      "disputed": false,
      "dev_pct": null,
      "tol_pct": 5,
      "gated": false,
      "within": null,
      "note": "V2a plate — third gain stage (100 kΩ load), DC-coupled to the cathode follower",
      "dispute_note": ""
    },
    {
      "node": "K2A",
      "chart": null,
      "sim": 1.385,
      "disputed": false,
      "dev_pct": null,
      "tol_pct": 5,
      "gated": false,
      "within": null,
      "note": "V2a cathode (820 Ω, unbypassed)",
      "dispute_note": ""
    },
    {
      "node": "KCF",
      "chart": null,
      "sim": 219.668,
      "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": 258.259,
      "disputed": false,
      "dev_pct": null,
      "tol_pct": 5,
      "gated": false,
      "within": null,
      "note": "phase-inverter plate, 82 kΩ side (V3a — the driven side, fed from the master volume)",
      "dispute_note": ""
    },
    {
      "node": "PPIB",
      "chart": null,
      "sim": 248.083,
      "disputed": false,
      "dev_pct": null,
      "tol_pct": 5,
      "gated": false,
      "within": null,
      "note": "phase-inverter plate, 100 kΩ side (V3b)",
      "dispute_note": ""
    },
    {
      "node": "KPI",
      "chart": null,
      "sim": 44.613,
      "disputed": false,
      "dev_pct": null,
      "tol_pct": 5,
      "gated": false,
      "within": null,
      "note": "phase-inverter shared cathode over the 470 Ω cathode resistor",
      "dispute_note": ""
    },
    {
      "node": "JPI",
      "chart": null,
      "sim": 43.212,
      "disputed": false,
      "dev_pct": null,
      "tol_pct": 5,
      "gated": false,
      "within": null,
      "note": "phase-inverter tail junction — both 1 MΩ grid leaks return here, above the 10 kΩ tail",
      "dispute_note": ""
    },
    {
      "node": "NNFB",
      "chart": null,
      "sim": 13.388,
      "disputed": false,
      "dev_pct": null,
      "tol_pct": 5,
      "gated": false,
      "within": null,
      "note": "negative-feedback node at the foot of the tail: 4.7 kΩ to ground, 100 kΩ back to the output-transformer secondary, presence leg capacitor-blocked",
      "dispute_note": ""
    },
    {
      "node": "SG4",
      "chart": null,
      "sim": 469.592,
      "disputed": false,
      "dev_pct": null,
      "tol_pct": 5,
      "gated": false,
      "within": null,
      "note": "V4 screen grid, through its 1.5 kΩ screen resistor (the corpus's EL34 fit draws no screen current at this bias, so the drop reads as zero — see the circuit story)",
      "dispute_note": ""
    },
    {
      "node": "SG5",
      "chart": null,
      "sim": 469.592,
      "disputed": false,
      "dev_pct": null,
      "tol_pct": 5,
      "gated": false,
      "within": null,
      "note": "V5 screen grid, through its 1.5 kΩ screen resistor",
      "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: C17, C4, C5, F1, F2, R14, R2, R3, R35, R36, R37. 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 2204; this board is derived from the factory drawing sheets, 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": "6 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/m2204"
}