{
  "format": "circuit-codex-reference",
  "version": 1,
  "id": "m1959",
  "url": "https://circuitcodex.com/amps/m1959/",
  "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": "m1959",
    "name_style": "Super Lead 100-style",
    "family": "british",
    "era": {
      "start": 1965,
      "end": 1981
    },
    "wattage": 100,
    "tubes": [
      "ECC83",
      "ECC83",
      "ECC83",
      "EL34",
      "EL34",
      "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": [
        "jtm45"
      ],
      "influenced": []
    },
    "conventions": {
      "designators": "functional"
    },
    "sources": [
      {
        "desc": "Marshall model 1959 factory drawing — Unicord drawing 70-6-11 rev B, dated July 1970 (Unicord Incorporated, 75 Frost Street, Westbury NY, a Gulf+Western company; Marshall's US importer). Title block reads 'MARSHALL 1959'; complement 3x ECC83 (V1/V2/V3) + 4x EL34 (V4-V7), silicon bridge rectifier (NO rectifier valve). Every component value read directly from the published drawing: four inputs across two channels (68k stoppers, 1M leaks, 100k plates; V1A cathode 820R/250uF, V1B cathode 2.7k/0.68uF; 0.022 and 0.0022 couplers); 470k mixers into 1M volumes with 0.005 and 500pF bright caps; V2A second stage (100k plate, 820R/0.68uF cathode, drawing annotates the 820R as '(1K)'); 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 (82k plate on the tone-stack side, 100k on the other, 470R + 10k tail, both 1M leaks to the junction, 47pF across the plates); 47k (100k annotated) feedback resistor and 5k presence pot with 0.1uF at the tail's cold end; four EL34s in parallel push-pull, 1k screen stoppers, 5.6k grid stoppers, two 120k grid leaks off a diode/15k/27k/47k bias supply with a 27k trimmer and 8uF filters; power 4x A10D10 bridge into 100uF+100uF series pairs with 56k balancing, 20k/1W then two 10k/1W droppers with 50uF+50uF pairs, universal mains taps 110/120/200/225/245. The drawing prints NO valve-voltage chart. Not reproduced here; archived at El34World.",
        "url": "https://el34world.com/charts/Schematics/files/Marshall/Marshall_jmp_superlead_100w_1959.pdf"
      },
      {
        "desc": "Marshall factory 'MARSHALL 100W. VOLT. CHART' — the published valve-voltage chart issued with the Unicord sheet of the same drawing number and date (70-6-11, July 1970) titled 'MARSHALL 1959 MARK II', whose ECC83 front end is closely related to the circuit documented here ahead of a 6550 output quartet. Its V1/V2/V3 rows are the chart this entry's operating points are checked against; its output rows (453 V plate, 450 V screen, bias approx -51 V, primary current 1.2-1.3 A at 120 V AC) describe the 6550 variant and are not claimed for the EL34 version.",
        "url": "https://el34world.com/charts/Schematics/files/Marshall/Marshall_1959mkii_volt_chrt.pdf"
      },
      {
        "desc": "Marshall '100 Watt Amplifier, Type #2, c.1967' — an undated hand-drawn schematic archived with the factory sheets, used as a cross-reference. It confirms the same topology at the earlier date (four inputs, 68k stoppers, 100k plates, 820R/2.7k cathodes, cathode-follower TMB stack, long-tailed-pair inverter, four output valves, silicon bridge) and boxes its own rail figures of 375 V at the phase inverter, 305 V at the second stage and 270 V at the input stage. It is an earlier supply: a 20 H choke, an 8.2k dropper down to the phase-inverter rail where the 1970 factory sheet uses 20k, and a 33k feed to the bias supply. The factory sheet is the source used here.",
        "url": "https://el34world.com/charts/Schematics/files/Marshall/Marshall_jmp_superlead_100w_1959.pdf"
      },
      {
        "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"
      },
      {
        "desc": "Wikipedia, 'Marshall Amplification' — the origin of the 100-watt heads as a special order from players wanting more than 45 watts on stage, the 1965 introduction of the 100-watt Super Lead as Marshall's catalog number 1959, its cost-driven move from KT66 to EL34 output valves, the 1969 change from the acrylic ('plexi') front panel to brushed metal, and the mid-1970s move to printed-circuit construction that closed the era this circuit belongs to",
        "url": "https://en.wikipedia.org/wiki/Marshall_Amplification"
      }
    ],
    "verification": {
      "status": "draft"
    },
    "added": "2026-08-02T00:00:00.000Z",
    "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. Where the drawing prints a second value in parentheses, that is a factory-annotated alternate: the primary value is listed and the alternate is named in the part's role. The HT-winding snubbers, the fuses, the standby switch and the pilot lamp are annotations on the factory sheet: the snubber capacitors appear on the schematic without connections, and the rest carry no designator. The output transformer is the one transformer the list numbers — T1; the mains/HT transformer is drawn as an annotation and is listed without a designator.",
    "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": "250 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 across the volume"
      },
      {
        "ref": "C6",
        "part": "Mica capacitor",
        "value": "500 pF",
        "role": "Channel II bright cap across the volume"
      },
      {
        "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; the published voltage chart's amp carries the 1 kΩ)"
      },
      {
        "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": "82 kΩ · ½ W",
        "role": "PI plate load (V3A, the tone-stack-driven side)"
      },
      {
        "ref": "RLB",
        "part": "Carbon comp resistor",
        "value": "100 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": "RNFB",
        "part": "Carbon comp resistor",
        "value": "47 kΩ · ½ W",
        "role": "Negative feedback, 8 Ω secondary tap → PI tail cold end (drawing annotates a 100 kΩ variant)"
      },
      {
        "ref": "VR6",
        "part": "Linear potentiometer",
        "value": "5 kΩ",
        "role": "Presence"
      },
      {
        "ref": "C13",
        "part": "Film capacitor",
        "value": "0.1 µF",
        "role": "Presence-pot wiper to ground"
      },
      {
        "ref": "C14",
        "part": "Film capacitor",
        "value": "0.1 µF",
        "role": "AC coupling from the presence/feedback node to the V3B grid"
      },
      {
        "ref": "C15",
        "part": "Coupling capacitor",
        "value": "0.022 µF · 400 V",
        "role": "PI (82 kΩ plate) → V4/V5 grid line"
      },
      {
        "ref": "C16",
        "part": "Coupling capacitor",
        "value": "0.022 µF · 400 V",
        "role": "PI (100 kΩ plate) → V6/V7 grid line"
      },
      {
        "ref": "RGL1",
        "part": "Carbon comp resistor",
        "value": "120 kΩ · ½ W",
        "role": "Grid leak for the V4/V5 pair, from the bias line"
      },
      {
        "ref": "RGL2",
        "part": "Carbon comp resistor",
        "value": "120 kΩ · ½ W",
        "role": "Grid leak for the V6/V7 pair, from the bias line"
      },
      {
        "ref": "RS4",
        "part": "Carbon comp resistor",
        "value": "5.6 kΩ · ½ W",
        "role": "V4 grid stopper"
      },
      {
        "ref": "RS5",
        "part": "Carbon comp resistor",
        "value": "5.6 kΩ · ½ W",
        "role": "V5 grid stopper"
      },
      {
        "ref": "RS6",
        "part": "Carbon comp resistor",
        "value": "5.6 kΩ · ½ W",
        "role": "V6 grid stopper"
      },
      {
        "ref": "RS7",
        "part": "Carbon comp resistor",
        "value": "5.6 kΩ · ½ W",
        "role": "V7 grid stopper"
      },
      {
        "ref": "RSC4",
        "part": "Carbon comp resistor",
        "value": "1 kΩ",
        "role": "V4 screen-grid stopper"
      },
      {
        "ref": "RSC5",
        "part": "Carbon comp resistor",
        "value": "1 kΩ",
        "role": "V5 screen-grid stopper"
      },
      {
        "ref": "RSC6",
        "part": "Carbon comp resistor",
        "value": "1 kΩ",
        "role": "V6 screen-grid stopper"
      },
      {
        "ref": "RSC7",
        "part": "Carbon comp resistor",
        "value": "1 kΩ",
        "role": "V7 screen-grid stopper"
      },
      {
        "ref": "D1",
        "part": "Silicon rectifier diode",
        "value": "1008",
        "role": "Bias-supply rectifier — its own HT-tap diode"
      },
      {
        "ref": "RBA",
        "part": "Carbon comp resistor",
        "value": "27 kΩ · ½ W",
        "role": "Bias-supply series resistor, dedicated bias winding → diode (drawing annotates a 22 kΩ variant)"
      },
      {
        "ref": "RBB",
        "part": "Carbon comp resistor",
        "value": "15 kΩ · ½ W",
        "role": "Bias-supply series resistor between the two 8 µF filters"
      },
      {
        "ref": "RBC",
        "part": "Carbon comp resistor",
        "value": "47 kΩ · ½ W",
        "role": "Bias-adjust divider, upper leg"
      },
      {
        "ref": "VR7",
        "part": "Trim potentiometer",
        "value": "27 kΩ",
        "role": "Bias adjust"
      },
      {
        "ref": "C17",
        "part": "Electrolytic capacitor",
        "value": "8 µF",
        "role": "Bias-supply filter"
      },
      {
        "ref": "C18",
        "part": "Electrolytic capacitor",
        "value": "8 µF",
        "role": "Bias-supply filter"
      },
      {
        "ref": "RD1",
        "part": "Power resistor",
        "value": "20 kΩ · 1 W",
        "role": "Rail dropper B+1 (reservoir / screens) → B+2 (phase inverter)"
      },
      {
        "ref": "RD2",
        "part": "Power resistor",
        "value": "10 kΩ · 1 W",
        "role": "Rail dropper B+2 (phase inverter) → B+3 (second stage / cathode follower)"
      },
      {
        "ref": "RD3",
        "part": "Power resistor",
        "value": "10 kΩ · 1 W",
        "role": "Rail dropper B+3 (second stage) → B+4 (input stage)"
      },
      {
        "ref": "C19",
        "part": "Electrolytic capacitor",
        "value": "100 µF · 350 V",
        "role": "Reservoir filter, upper half of a series pair"
      },
      {
        "ref": "C20",
        "part": "Electrolytic capacitor",
        "value": "100 µF · 350 V",
        "role": "Reservoir filter, lower half of a series pair"
      },
      {
        "ref": "C21",
        "part": "Electrolytic capacitor",
        "value": "100 µF · 350 V",
        "role": "Second reservoir bank, upper half of a series pair"
      },
      {
        "ref": "C22",
        "part": "Electrolytic capacitor",
        "value": "100 µF · 350 V",
        "role": "Second reservoir bank, lower half of a series pair"
      },
      {
        "ref": "RB1",
        "part": "Carbon comp resistor",
        "value": "56 kΩ",
        "role": "Voltage-sharing resistor across a series reservoir capacitor"
      },
      {
        "ref": "RB2",
        "part": "Carbon comp resistor",
        "value": "56 kΩ",
        "role": "Voltage-sharing resistor across a series reservoir capacitor"
      },
      {
        "ref": "C23",
        "part": "Electrolytic capacitor",
        "value": "50 µF · 350 V",
        "role": "Phase-inverter-supply filter"
      },
      {
        "ref": "C24",
        "part": "Electrolytic capacitor",
        "value": "50 µF · 350 V",
        "role": "Phase-inverter-supply filter"
      },
      {
        "ref": "C25",
        "part": "Electrolytic capacitor",
        "value": "50 µF · 350 V",
        "role": "Second-stage-supply filter"
      },
      {
        "ref": "C26",
        "part": "Electrolytic capacitor",
        "value": "50 µF · 350 V",
        "role": "Second-stage-supply filter"
      },
      {
        "ref": "C27",
        "part": "Electrolytic capacitor",
        "value": "50 µF · 350 V",
        "role": "Input-stage-supply filter"
      },
      {
        "ref": "C28",
        "part": "Electrolytic capacitor",
        "value": "50 µF · 350 V",
        "role": "Input-stage-supply filter"
      },
      {
        "ref": "D2",
        "part": "Silicon rectifier diode",
        "value": "A10D10",
        "role": "HT bridge rectifier arm"
      },
      {
        "ref": "D3",
        "part": "Silicon rectifier diode",
        "value": "A10D10",
        "role": "HT bridge rectifier arm"
      },
      {
        "ref": "D4",
        "part": "Silicon rectifier diode",
        "value": "A10D10",
        "role": "HT bridge rectifier arm"
      },
      {
        "ref": "D5",
        "part": "Silicon rectifier diode",
        "value": "A10D10",
        "role": "HT bridge rectifier arm"
      },
      {
        "ref": "C29",
        "part": "Film capacitor",
        "value": "0.22 µF",
        "role": "HT-winding snubber"
      },
      {
        "ref": "C30",
        "part": "Film capacitor",
        "value": "0.22 µF",
        "role": "HT-winding snubber"
      },
      {
        "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": "Parallel push-pull output — phase A"
      },
      {
        "ref": "V5",
        "part": "Power tube",
        "value": "EL34",
        "role": "Parallel push-pull output — phase A"
      },
      {
        "ref": "V6",
        "part": "Power tube",
        "value": "EL34",
        "role": "Parallel push-pull output — phase B"
      },
      {
        "ref": "V7",
        "part": "Power tube",
        "value": "EL34",
        "role": "Parallel push-pull output — phase B"
      },
      {
        "ref": "T1",
        "part": "Output transformer",
        "value": "16/8/4 Ω taps",
        "role": "Output transformer — parallel push-pull primary for four EL34s, 16/8/4 Ω secondary taps (feedback from the 8 Ω tap)"
      },
      {
        "ref": "—",
        "part": "Power transformer",
        "value": "Universal primary 110/120/200/225/245 V · HT, bias and 6.3 V heater windings",
        "role": "Mains/HT transformer, with a separate bias winding (one end to chassis) feeding the bias rectifier"
      },
      {
        "ref": "—",
        "part": "Fuse",
        "value": "4 A",
        "role": "Mains fuse (annotation)"
      },
      {
        "ref": "—",
        "part": "Fuse",
        "value": "1 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)"
      }
    ]
  },
  "publishedVoltages": {
    "source": "Marshall factory 'MARSHALL 100W. VOLT. CHART' published with Unicord drawing 70-6-11, July 1970 ('MARSHALL 1959 MARK II'): V1 pins 1/3/6/8 = 135 / 1.0 / 195 / 1.5; V2 pins 1/3/6/7/8 = 153 / 1.1 / 260 / 153 / 153; V3 pins 1/3/6/8 = 210 / 18.5 / 195 / 18.5; V4-V7 (6550) pins 3/4/5 = 453 / 450 / -51; footnote 'Bias approx. -51 vdc; primary current 1.2 - 1.3 amps at 120 vac'.",
    "nodes": {
      "P1A": {
        "chart": 135,
        "tol_pct": 20,
        "note": "V1A plate — channel I (high-treble) input, 100 kΩ load, 820 Ω cathode (chart V1 pin 1)"
      },
      "K1A": {
        "chart": 1,
        "tol_pct": 20,
        "note": "V1A cathode (820 Ω, 250 µF bypass) — chart V1 pin 3"
      },
      "P1B": {
        "chart": 195,
        "tol_pct": 20,
        "note": "V1B plate — channel II (normal) input, 100 kΩ load (chart V1 pin 6)"
      },
      "K1B": {
        "chart": 1.5,
        "tol_pct": 20,
        "note": "V1B cathode (2.7 kΩ, 0.68 µF partial bypass) — the colder channel; chart V1 pin 8"
      },
      "P2A": {
        "chart": 153,
        "tol_pct": 20,
        "note": "V2A plate — second gain stage (100 kΩ load), DC-coupled to the cathode follower; chart V2 pin 1"
      },
      "K2A": {
        "chart": 1.1,
        "tol_pct": 20,
        "note": "V2A cathode — chart V2 pin 3. The chart amp carries the 1 kΩ cathode resistor the drawing annotates as a variant; the netlist uses the drawing's primary 820 Ω, which idles this stage slightly hotter."
      },
      "KCF": {
        "chart": 153,
        "tol_pct": 20,
        "note": "V2B cathode-follower output over its 100 kΩ load, feeding the TMB tone stack (chart V2 pin 8)"
      },
      "PPIA": {
        "chart": 210,
        "tol_pct": 20,
        "note": "phase-inverter plate, 82 kΩ side (V3A, driven from the tone stack); chart V3 pin 1"
      },
      "PPIB": {
        "chart": 195,
        "tol_pct": 20,
        "note": "phase-inverter plate, 100 kΩ side (V3B, the AC-grounded side); chart V3 pin 6"
      },
      "KPI": {
        "chart": 18.5,
        "tol_pct": 20,
        "disputed": true,
        "note": "phase-inverter shared cathode above the 470 Ω (chart V3 pins 3 and 8). The drawn 10 kΩ tail ends at the 5 kΩ presence track in parallel with the 47 kΩ feedback return; this circuit simulates about 36.5 V. The drawn return is kept; the chart is not used to change it.",
        "dispute_note": "The printed figures fit a tail neither drawing shows. The printed plates (+210 V through 82 kΩ and +195 V through 100 kΩ, off a supply near +283 V) carry 0.89 + 0.88 = 1.77 mA, and 1.77 mA through the 470 Ω + 10 kΩ alone gives 18.5 V: the printed cathode, exactly, but only if the 10 kΩ returns straight to ground. Both the EL34 drawing and the 6550 Mark II drawing the chart was issued with end the 10 kΩ at the 5 kΩ presence track (lower lug grounded) in parallel with the 47 kΩ feedback, about 4.5 kΩ more; through 14.99 kΩ the same 1.77 mA would put the cathode near 26.5 V, and the printed 18.5 V would leave only 1.23 mA, too little for the printed plates. The chart's cathode and plate figures are consistent with each other and with neither drawing, so they are recorded as printed and disputed rather than fitted."
      },
      "BP2": {
        "chart": null,
        "note": "phase-inverter supply node, after the 20 kΩ/1 W dropper — no chart pin. The chart's own stage currents put it near 300 V"
      },
      "BP3": {
        "chart": 260,
        "tol_pct": 20,
        "note": "second-stage / cathode-follower supply node after the first 10 kΩ/1 W dropper — read from the cathode follower's plate, chart V2 pin 6"
      },
      "BP4": {
        "chart": null,
        "note": "input-stage supply node after the second 10 kΩ/1 W dropper — no chart pin; the chart's V1 plate and cathode figures put it near 254 V"
      },
      "JPI": {
        "chart": null,
        "note": "phase-inverter tail junction between the 470 Ω and the 10 kΩ, where both 1 MΩ grid leaks return"
      },
      "SG4": {
        "chart": null,
        "note": "V4 screen grid after its 1 kΩ stopper — the only published figure is the 6550 variant's 450 V. The anchor-point EL34 model draws no screen current at this operating point, so the simulated node sits exactly at B+1"
      },
      "G4": {
        "chart": null,
        "note": "V4 control grid, fed from the adjustable bias supply through the 120 kΩ leak and a 5.6 kΩ stopper — the drawing prints no bias figure and the only published one is the 6550 variant's -51 V"
      }
    }
  },
  "operatingPoint": [
    {
      "node": "P1A",
      "chart": 135,
      "sim": 141.684,
      "disputed": false,
      "dev_pct": 4.95111111111111,
      "tol_pct": 20,
      "gated": true,
      "within": true,
      "note": "V1A plate — channel I (high-treble) input, 100 kΩ load, 820 Ω cathode (chart V1 pin 1)",
      "dispute_note": ""
    },
    {
      "node": "K1A",
      "chart": 1,
      "sim": 0.91,
      "disputed": false,
      "dev_pct": 8.999999999999996,
      "tol_pct": 20,
      "gated": true,
      "within": true,
      "note": "V1A cathode (820 Ω, 250 µF bypass) — chart V1 pin 3",
      "dispute_note": ""
    },
    {
      "node": "P1B",
      "chart": 195,
      "sim": 187.73,
      "disputed": false,
      "dev_pct": 3.7282051282051336,
      "tol_pct": 20,
      "gated": true,
      "within": true,
      "note": "V1B plate — channel II (normal) input, 100 kΩ load (chart V1 pin 6)",
      "dispute_note": ""
    },
    {
      "node": "K1B",
      "chart": 1.5,
      "sim": 1.754,
      "disputed": false,
      "dev_pct": 16.933333333333334,
      "tol_pct": 20,
      "gated": true,
      "within": true,
      "note": "V1B cathode (2.7 kΩ, 0.68 µF partial bypass) — the colder channel; chart V1 pin 8",
      "dispute_note": ""
    },
    {
      "node": "P2A",
      "chart": 153,
      "sim": 151.796,
      "disputed": false,
      "dev_pct": 0.7869281045751684,
      "tol_pct": 20,
      "gated": true,
      "within": true,
      "note": "V2A plate — second gain stage (100 kΩ load), DC-coupled to the cathode follower; chart V2 pin 1",
      "dispute_note": ""
    },
    {
      "node": "K2A",
      "chart": 1.1,
      "sim": 0.972,
      "disputed": false,
      "dev_pct": 11.636363636363646,
      "tol_pct": 20,
      "gated": true,
      "within": true,
      "note": "V2A cathode — chart V2 pin 3. The chart amp carries the 1 kΩ cathode resistor the drawing annotates as a variant; the netlist uses the drawing's primary 820 Ω, which idles this stage slightly hotter.",
      "dispute_note": ""
    },
    {
      "node": "KCF",
      "chart": 153,
      "sim": 152.102,
      "disputed": false,
      "dev_pct": 0.5869281045751609,
      "tol_pct": 20,
      "gated": true,
      "within": true,
      "note": "V2B cathode-follower output over its 100 kΩ load, feeding the TMB tone stack (chart V2 pin 8)",
      "dispute_note": ""
    },
    {
      "node": "PPIA",
      "chart": 210,
      "sim": 209.255,
      "disputed": false,
      "dev_pct": 0.35476190476190694,
      "tol_pct": 20,
      "gated": true,
      "within": true,
      "note": "phase-inverter plate, 82 kΩ side (V3A, driven from the tone stack); chart V3 pin 1",
      "dispute_note": ""
    },
    {
      "node": "PPIB",
      "chart": 195,
      "sim": 200.377,
      "disputed": false,
      "dev_pct": 2.7574358974359026,
      "tol_pct": 20,
      "gated": true,
      "within": true,
      "note": "phase-inverter plate, 100 kΩ side (V3B, the AC-grounded side); chart V3 pin 6",
      "dispute_note": ""
    },
    {
      "node": "KPI",
      "chart": 18.5,
      "sim": 36.502,
      "disputed": true,
      "dev_pct": 97.30810810810813,
      "tol_pct": 20,
      "gated": false,
      "within": null,
      "note": "phase-inverter shared cathode above the 470 Ω (chart V3 pins 3 and 8). The drawn 10 kΩ tail ends at the 5 kΩ presence track in parallel with the 47 kΩ feedback return; this circuit simulates about 36.5 V. The drawn return is kept; the chart is not used to change it.",
      "dispute_note": "The printed figures fit a tail neither drawing shows. The printed plates (+210 V through 82 kΩ and +195 V through 100 kΩ, off a supply near +283 V) carry 0.89 + 0.88 = 1.77 mA, and 1.77 mA through the 470 Ω + 10 kΩ alone gives 18.5 V: the printed cathode, exactly, but only if the 10 kΩ returns straight to ground. Both the EL34 drawing and the 6550 Mark II drawing the chart was issued with end the 10 kΩ at the 5 kΩ presence track (lower lug grounded) in parallel with the 47 kΩ feedback, about 4.5 kΩ more; through 14.99 kΩ the same 1.77 mA would put the cathode near 26.5 V, and the printed 18.5 V would leave only 1.23 mA, too little for the printed plates. The chart's cathode and plate figures are consistent with each other and with neither drawing, so they are recorded as printed and disputed rather than fitted."
    },
    {
      "node": "BP2",
      "chart": null,
      "sim": 314.972,
      "disputed": false,
      "dev_pct": null,
      "tol_pct": 5,
      "gated": false,
      "within": null,
      "note": "phase-inverter supply node, after the 20 kΩ/1 W dropper — no chart pin. The chart's own stage currents put it near 300 V",
      "dispute_note": ""
    },
    {
      "node": "BP3",
      "chart": 260,
      "sim": 270.31,
      "disputed": false,
      "dev_pct": 3.9653846153846164,
      "tol_pct": 20,
      "gated": true,
      "within": true,
      "note": "second-stage / cathode-follower supply node after the first 10 kΩ/1 W dropper — read from the cathode follower's plate, chart V2 pin 6",
      "dispute_note": ""
    },
    {
      "node": "BP4",
      "chart": null,
      "sim": 252.709,
      "disputed": false,
      "dev_pct": null,
      "tol_pct": 5,
      "gated": false,
      "within": null,
      "note": "input-stage supply node after the second 10 kΩ/1 W dropper — no chart pin; the chart's V1 plate and cathode figures put it near 254 V",
      "dispute_note": ""
    },
    {
      "node": "JPI",
      "chart": null,
      "sim": 35.357,
      "disputed": false,
      "dev_pct": null,
      "tol_pct": 5,
      "gated": false,
      "within": null,
      "note": "phase-inverter tail junction between the 470 Ω and the 10 kΩ, where both 1 MΩ grid leaks return",
      "dispute_note": ""
    },
    {
      "node": "SG4",
      "chart": null,
      "sim": 453,
      "disputed": false,
      "dev_pct": null,
      "tol_pct": 5,
      "gated": false,
      "within": null,
      "note": "V4 screen grid after its 1 kΩ stopper — the only published figure is the 6550 variant's 450 V. The anchor-point EL34 model draws no screen current at this operating point, so the simulated node sits exactly at B+1",
      "dispute_note": ""
    },
    {
      "node": "G4",
      "chart": null,
      "sim": -46,
      "disputed": false,
      "dev_pct": null,
      "tol_pct": 5,
      "gated": false,
      "within": null,
      "note": "V4 control grid, fed from the adjustable bias supply through the 120 kΩ leak and a 5.6 kΩ stopper — the drawing prints no bias figure and the only published one is the 6550 variant's -51 V",
      "dispute_note": ""
    }
  ],
  "checks": [
    {
      "id": "dc",
      "title": "DC operating point",
      "status": "Within target",
      "summary": "10 reference nodes are within tolerance. The circuit remains a draft awaiting maintainer review.",
      "details": [
        "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.",
        "11 sheet-only parts are explicitly excluded: C13, C29, C30, C5, C6, 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, V2, V3.",
        "No Marshall board-layout sheet was located for the model 1959; 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": "13 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/m1959"
}