{
  "format": "circuit-codex-reference",
  "version": 1,
  "id": "6g2",
  "url": "https://circuitcodex.com/amps/6g2/",
  "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": "6g2",
    "name_style": "Brown Princeton-style",
    "family": "other",
    "era": {
      "start": 1961,
      "end": 1963
    },
    "wattage": 12,
    "tubes": [
      7025,
      "12AX7",
      "6V6GT",
      "6V6GT",
      "5Y3GT"
    ],
    "topology": {
      "rectifier": {
        "kind": "tube",
        "type": "5Y3GT"
      },
      "bias": "fixed",
      "phase_inverter": "cathodyne",
      "tone_stack": "single-knob"
    },
    "lineage": {
      "derived_from": [],
      "influenced": [
        "aa964"
      ]
    },
    "conventions": {
      "designators": "functional"
    },
    "sources": [
      {
        "desc": "Fender 'Princeton' Model 6G2 drawing (H-FA), schematic + layout: every component value AND the printed voltage chart read directly from the published sheet (+315 reservoir/OT centre tap, +312 screen node, +280 preamp/PI rail, +230 cathodyne plate, +200 tremolo-oscillator plate, +135 both 7025 plates (printed on both pages, and disputed: +1.5 V over each 1500 ohm cathode resistor puts the plates near +180) with +1.5 shared-type cathodes, cathodyne cathode +56.5 over a 1000 ohm resistor into a +55 tail, -35 fixed bias; two-jack input 68k stoppers/1M leak; 7025 V1A 100k plate/1.5k-25uF cathode, V1B 100k plate/1.5k cathode unbypassed, with a 56k negative-feedback resistor from the speaker line landing on that cathode; cathodyne (12AX7) 56k plate load, 1000 ohm cathode resistor into a tail junction, 56k tail-to-ground, 1M grid leak returned to the tail (not ground); 6V6GT pair grounded cathodes, each grid behind a 1500 ohm stopper (mounted at the socket) on a coupler node that a 220k-5% leak returns to the -35 V bias line, which is the Intensity control's wiper — the Intensity pot itself sits in that line (one end at the fixed-bias supply, the other AC-coupled to the tremolo oscillator through a .1 uF cap); tremolo oscillator on the other 12AX7 half, phase-shift type, 220k plate load off the raw reservoir, a .02/.01/.01 ladder with 1M to the cathode and 1M to ground, 3300/25uF cathode, Speed 3M-RA with 100k in series, the pedal jack on the ladder's middle node, output into the Intensity control through 220k + .1 uF; bias supply 100k-5% + rectifier + 25uF/50V + 30k-5% bleeder. TR1 125P1A, TR2 125A10B. Notice: values +/-20%, read to ground with an electronic voltmeter, resistors 1/2 W 10% unless marked, capacitors at least 400 V unless marked. The cathodyne cathode resistor is read as printed, 1000 ohm: the 800 ppi layout page settles it (its glyphs match the same page's 1000 ohm dropper, not V1A's 1500); the 72 ppi schematic is too coarse to decide. Until the 2026-10-03 V1 audit the corpus carried 1.5 kOhm, chosen to fit the printed +56.5/+55 V chart pair rather than read; at 1000 ohm those two nodes simulate 11-12% high, inside the sheet's +/-20%. Not reproduced here; archived at EL34World",
        "url": "https://el34world.com/charts/Schematics/files/Fender/Fender_princeton_6g2_schem.pdf"
      },
      {
        "desc": "Fender 'Princeton' Model 6G2 layout drawing (H-FA): the physical order of the board/eyelet parts, the socket pin numbering for the 5Y3GT/6V6GT/12AX7/7025 sockets, and the transformer/wire-colour callouts, resolved lead by lead on the Internet Archive's capture of this PDF at its native 6510 x 4752 (800 ppi): the PT's six-lead fan letters, left to right, YELLOW / RED / RED / YELLOW / BLACK / BLACK, and the two reds land on the 5Y3GT's plates at pins 4 and 6 while the two yellows are the rectifier's own 5 V filament winding at pins 2 and 8 and the two blacks run off to the fuse and the AC switch as the mains primary; a GREEN and the RED-YELLOW HT centre tap leave the other face tied together to ground, and the second GREEN feeds the pilot light and the arrow 'TO ALL 6.3 VOLT HTRS.' (an earlier reading of a lower-resolution copy of this sheet gave the rectifier filament as the black pair and left the second yellow pair unasserted); OT blue/brown to the 6V6 plates, red centre tap, green to the speaker jacks. Confirms the two 6V6GT sockets and the +315 V pin annotation against the schematic. Not reproduced here; archived at EL34World",
        "url": "https://el34world.com/charts/Schematics/files/Fender/Fender_princeton_6g2.pdf"
      },
      {
        "desc": "Fender 'Princeton-Amp AA964' schematic (drawing 045419) — cross-reference for the 6G2's own cathodyne, which the AA964's own published values (56 k plate load, 1 k cathode resistor to a 56 k tail, 1 M grid leak returned to that junction) closely match in topology; used here only to corroborate the tail-to-ground resistor read as 56 k on the 6G2 sheet where the scan is faint, never to substitute a value the 6G2 drawing itself does not carry",
        "url": "https://el34world.com/charts/Schematics/files/Fender/Fender_princeton_AA964_schem.pdf"
      },
      {
        "desc": "Fender 'Harvard' Model 5F10 drawing (F-EF) — second cross-reference for the same cathodyne family recipe (56 k plate + small cathode R into a tail, 56 k tail-to-ground, 1 M leak returned to the tail), a contemporaneous fixed-bias 6V6 Fender design sharing the identical PI topology",
        "url": "https://el34world.com/charts/Schematics/files/Fender/Fender_harvard_5f10_schem.pdf"
      },
      {
        "desc": "Mojotone Fender Field Guide, 'Fender Brownface Princeton' — production window 1961-1963, 12 W rating, push-pull 2x6V6GT with phase inverter, fixed bias, 5Y3GT rectifier",
        "url": "https://mojotone.com/blogs/fender-field-guide/fender-brownface-princeton"
      }
    ],
    "verification": {
      "status": "verified",
      "date": "2026-08-08T00:00:00.000Z",
      "max_deviation_pct": 12.1
    },
    "added": "2026-08-08T00:00:00.000Z",
    "contributors": [
      "TheAnalogMaker"
    ],
    "sections": {
      "V2B": "excluded — the tremolo's phase-shift oscillator: a running oscillator has no static operating point; its 56k plate load taps the driven node BP, so nothing downstream moves"
    }
  },
  "parts": {
    "notes": "Each input jack has its own 68 kΩ stopper into the grid; the 1 MΩ leak hangs at jack 1's tip, jack side of its stopper (jack 2's contact → jack 1's tip, jack 1's contact → ground), as both H-FA pages draw it. The tremolo oscillator's own parts are listed for the record; its DC operating point is excluded from the netlist (see the circuit story). Parts drawn only as annotations — mains cap, fuse, switches, pilot lamp — are listed without designators. The two transformers are numbered T1 (power) and T2 (output) under the archive's convention; the drawing's own labels are TR1 and TR2.",
    "items": [
      {
        "ref": "R1",
        "part": "Carbon comp resistor",
        "value": "68 kΩ · ½ W",
        "role": "Input grid stopper (jack 1)"
      },
      {
        "ref": "R2",
        "part": "Carbon comp resistor",
        "value": "68 kΩ · ½ W",
        "role": "Input grid stopper (jack 2)"
      },
      {
        "ref": "RG1",
        "part": "Carbon comp resistor",
        "value": "1 MΩ · ½ W",
        "role": "Input leak, jack 1's tip to ground (jack side of R1); V1A's DC grid return through R1"
      },
      {
        "ref": "RL1",
        "part": "Carbon comp resistor",
        "value": "100 kΩ · ½ W",
        "role": "V1A plate load"
      },
      {
        "ref": "RK1",
        "part": "Carbon comp resistor",
        "value": "1.5 kΩ · ½ W",
        "role": "V1A cathode bias"
      },
      {
        "ref": "C1",
        "part": "Electrolytic capacitor",
        "value": "25 µF · 25 V",
        "role": "V1A cathode bypass"
      },
      {
        "ref": "C2",
        "part": "Coupling capacitor",
        "value": "0.02 µF · 400 V",
        "role": "V1A plate → Tone/Volume network"
      },
      {
        "ref": "VR1",
        "part": "Audio-taper potentiometer",
        "value": "1 MΩ-A",
        "role": "Tone — single-knob blend: wiper on the Volume's top lug (the coupler node), one end to ground through C5, the other to the Volume wiper through C3"
      },
      {
        "ref": "C3",
        "part": "Capacitor",
        "value": "500 pF",
        "role": "Tone pot end → Volume wiper (V1B grid); printed .0005"
      },
      {
        "ref": "C5",
        "part": "Capacitor",
        "value": "0.005 µF · 400 V",
        "role": "Tone pot end → ground; printed .005 on both pages"
      },
      {
        "ref": "VR2",
        "part": "Audio-taper potentiometer",
        "value": "1 MΩ-A",
        "role": "Volume"
      },
      {
        "ref": "RG2",
        "part": "—",
        "value": "—",
        "role": "V1B grid sits directly on the Volume wiper and returns to ground through the Volume pot's own track — no discrete leak resistor; modelled in the DC netlist as a nominal 1 MΩ, since no grid current flows and the pot's own value is not load-bearing"
      },
      {
        "ref": "RL2",
        "part": "Carbon comp resistor",
        "value": "100 kΩ · ½ W",
        "role": "V1B plate load"
      },
      {
        "ref": "RK2",
        "part": "Carbon comp resistor",
        "value": "1.5 kΩ · ½ W",
        "role": "V1B cathode bias, unbypassed — the drawing's only 25 µF cathode can is V1A's"
      },
      {
        "ref": "RNFB",
        "part": "Carbon comp resistor",
        "value": "56 kΩ · ½ W",
        "role": "Global negative feedback, speaker line → V1B cathode"
      },
      {
        "ref": "C6",
        "part": "Coupling capacitor",
        "value": "0.02 µF · 400 V",
        "role": "V1B plate → cathodyne grid"
      },
      {
        "ref": "RL3",
        "part": "Carbon comp resistor",
        "value": "56 kΩ · ½ W",
        "role": "Cathodyne plate load"
      },
      {
        "ref": "RGPI",
        "part": "Carbon comp resistor",
        "value": "1 MΩ · ½ W",
        "role": "Cathodyne grid leak, returned to the tail junction (not ground)"
      },
      {
        "ref": "RKA",
        "part": "Carbon comp resistor",
        "value": "1 kΩ · ½ W",
        "role": "Cathodyne cathode resistor, into the tail junction. The H-FA layout page prints 1000 (crop 3760,2600,4000,2850; it matches the same page's 1000 Ω dropper, not V1A's 1500); the 72 ppi schematic is too coarse to decide. Until the 2026-10-03 V1 audit (6g2.md) the corpus carried 1.5 kΩ, a value chosen to fit the printed +56.5 V / +55 V chart pair, not read from the drawing"
      },
      {
        "ref": "RKB",
        "part": "Carbon comp resistor",
        "value": "56 kΩ · ½ W",
        "role": "Cathodyne tail-to-ground resistor; printed 56K on both H-FA pages, crisp on the 800 ppi layout (crop 3400,2050,4500,3750)"
      },
      {
        "ref": "C7",
        "part": "Coupling capacitor",
        "value": "0.1 µF · 400 V",
        "role": "Cathodyne plate → V3's coupler node"
      },
      {
        "ref": "C8",
        "part": "Coupling capacitor",
        "value": "0.1 µF · 400 V",
        "role": "Cathodyne cathode pin (+56.5 V) → V4's coupler node; taken off the cathode, not the tail junction, on both pages"
      },
      {
        "ref": "RL4",
        "part": "Carbon comp resistor",
        "value": "220 kΩ · ½ W",
        "role": "Oscillator plate load, off the +315 V reservoir (BP)"
      },
      {
        "ref": "RKTO",
        "part": "Carbon comp resistor",
        "value": "3.3 kΩ · ½ W",
        "role": "Oscillator cathode bias"
      },
      {
        "ref": "CKTO",
        "part": "Electrolytic capacitor",
        "value": "25 µF · 25 V",
        "role": "Oscillator cathode bypass"
      },
      {
        "ref": "CTO1",
        "part": "Coupling capacitor",
        "value": "0.02 µF · 400 V",
        "role": "Phase-shift ladder: plate → the Speed node"
      },
      {
        "ref": "VR3",
        "part": "Reverse-audio potentiometer",
        "value": "3 MΩ-RA",
        "role": "Speed — a rheostat from the Speed node, its wiper strapped to the far lug"
      },
      {
        "ref": "R3",
        "part": "Carbon comp resistor",
        "value": "100 kΩ · ½ W",
        "role": "Speed rheostat's series resistor to ground"
      },
      {
        "ref": "CTO2",
        "part": "Coupling capacitor",
        "value": "0.01 µF · 400 V",
        "role": "Phase-shift ladder: Speed node → the pedal node"
      },
      {
        "ref": "RTO1",
        "part": "Carbon comp resistor",
        "value": "1 MΩ · ½ W",
        "role": "Phase-shift ladder: pedal node → oscillator cathode"
      },
      {
        "ref": "CTO3",
        "part": "Coupling capacitor",
        "value": "0.01 µF · 400 V",
        "role": "Phase-shift ladder: pedal node → oscillator grid"
      },
      {
        "ref": "RTO2",
        "part": "Carbon comp resistor",
        "value": "1 MΩ · ½ W",
        "role": "Oscillator grid leak to ground"
      },
      {
        "ref": "R4",
        "part": "Carbon comp resistor",
        "value": "220 kΩ · ½ W",
        "role": "Oscillator output feed to the Intensity control"
      },
      {
        "ref": "C9",
        "part": "Coupling capacitor",
        "value": "0.1 µF · 400 V",
        "role": "Oscillator output coupling to the Intensity control"
      },
      {
        "ref": "VR4",
        "part": "Linear potentiometer",
        "value": "250 kΩ-L",
        "role": "Intensity — sits directly in the -35 V bias line; its wiper is the line both 220 kΩ grid leaks return to; carries no DC (see the DC netlist header)"
      },
      {
        "ref": "C10",
        "part": "Film capacitor",
        "value": "0.05 µF · 200 V",
        "role": "Intensity wiper to ground"
      },
      {
        "ref": "JTR",
        "part": "Jack",
        "value": "tremolo pedal",
        "role": "Tremolo pedal jack — its tip is on the ladder's pedal node, so the pedal's switch grounds that node and stops the oscillator"
      },
      {
        "ref": "RGL3",
        "part": "Carbon comp resistor",
        "value": "220 kΩ · 5 % · ½ W",
        "role": "V3 grid leak, from the -35 V bias line to V3's coupler node"
      },
      {
        "ref": "RG3",
        "part": "Carbon comp resistor",
        "value": "1.5 kΩ · ½ W",
        "role": "V3 grid stopper, coupler node → grid"
      },
      {
        "ref": "RGL4",
        "part": "Carbon comp resistor",
        "value": "220 kΩ · 5 % · ½ W",
        "role": "V4 grid leak, from the -35 V bias line to V4's coupler node"
      },
      {
        "ref": "RG4",
        "part": "Carbon comp resistor",
        "value": "1.5 kΩ · ½ W",
        "role": "V4 grid stopper, coupler node → grid"
      },
      {
        "ref": "RD1",
        "part": "Power resistor",
        "value": "1 kΩ · 1 W",
        "role": "Rail dropper +315 V → +312 V (screens)"
      },
      {
        "ref": "RD2",
        "part": "Power resistor",
        "value": "10 kΩ · 1 W",
        "role": "Rail dropper +312 V → +280 V (preamp/PI)"
      },
      {
        "ref": "C11",
        "part": "Electrolytic capacitor",
        "value": "30 µF · 450 V",
        "role": "Reservoir filter, +315 V"
      },
      {
        "ref": "C12",
        "part": "Electrolytic capacitor",
        "value": "30 µF · 450 V",
        "role": "Filter, +312 V screen node"
      },
      {
        "ref": "C13",
        "part": "Electrolytic capacitor",
        "value": "30 µF · 450 V",
        "role": "Filter, +280 V preamp/PI node"
      },
      {
        "ref": "R5",
        "part": "Carbon comp resistor",
        "value": "100 kΩ · 5 % · ½ W",
        "role": "Bias-supply feed from the HT winding"
      },
      {
        "ref": "D1",
        "part": "Rectifier (bias)",
        "value": "rectifier diode (type not printed) · silicon diode in modern builds",
        "role": "Bias-supply rectifier; both H-FA pages draw a plain diode symbol and name no type"
      },
      {
        "ref": "C14",
        "part": "Electrolytic capacitor",
        "value": "25 µF · 50 V",
        "role": "Bias-supply filter"
      },
      {
        "ref": "R6",
        "part": "Carbon comp resistor",
        "value": "30 kΩ · 5 % · ½ W",
        "role": "Bias-supply bleeder — sets the -35 V line"
      },
      {
        "ref": "V1",
        "part": "Preamp tube",
        "value": "7025 (12AX7)",
        "role": "Input + second stage (V1A/V1B)"
      },
      {
        "ref": "V2",
        "part": "Preamp tube",
        "value": "12AX7",
        "role": "Cathodyne phase inverter + tremolo oscillator (V2A/V2B)"
      },
      {
        "ref": "V3",
        "part": "Power tube",
        "value": "6V6GT",
        "role": "Push-pull output (plate-side drive)"
      },
      {
        "ref": "V4",
        "part": "Power tube",
        "value": "6V6GT",
        "role": "Push-pull output (tail-side drive)"
      },
      {
        "ref": "V5",
        "part": "Rectifier tube",
        "value": "5Y3GT",
        "role": "Full-wave rectifier"
      },
      {
        "ref": "T1",
        "part": "Power transformer",
        "value": "125P1A",
        "role": "HT + heaters + rectifier filament"
      },
      {
        "ref": "T2",
        "part": "Output transformer",
        "value": "125A10B",
        "role": "Push-pull output, centre-tapped primary"
      },
      {
        "ref": "—",
        "part": "Fuse",
        "value": "2 A",
        "role": "AC mains fuse (annotation only)"
      },
      {
        "ref": "—",
        "part": "Switch",
        "value": "SPST",
        "role": "AC power switch (annotation only)"
      },
      {
        "ref": "—",
        "part": "Switch",
        "value": "SPST",
        "role": "Ground (polarity) switch (annotation only)"
      },
      {
        "ref": "—",
        "part": "Film capacitor",
        "value": "0.05 µF · 600 V",
        "role": "Mains-to-chassis cap on the ground switch (annotation only)"
      },
      {
        "ref": "—",
        "part": "Pilot lamp",
        "value": "6.3 V",
        "role": "Pilot light (annotation only)"
      }
    ]
  },
  "publishedVoltages": {
    "source": "Fender 'Princeton' Model 6G2 (H-FA) drawing, printed voltages: +315 (reservoir / OT centre tap), +312 (6V6 screen node), +280 (preamp/PI rail), +230 (cathodyne plate), +135 (both 7025 plates, printed on the schematic and the layout page — disputed, see PA), +1.5 (both 7025 cathodes), cathodyne cathode +56.5 into a +55 tail junction, -35 (6V6 fixed bias, and the tremolo oscillator's own +200/oscillating plate, excluded — see the circuit story)",
    "nodes": {
      "BS": {
        "chart": 312,
        "tol_pct": 8,
        "note": "6V6 screen node, one 1000 Ohm-1W dropper below the driven reservoir — internal target, tighter than the drawing's own +/-20%"
      },
      "BD": {
        "chart": 280,
        "tol_pct": 8,
        "note": "preamp/PI rail, 10k-1W below the screen node — internal target"
      },
      "PA": {
        "chart": 135,
        "disputed": true,
        "dispute_note": "V1A (7025) plate, 100k off BD. Both pages of H-FA print +135 V here, the 3 unambiguous on the 800 ppi layout copy. The chart contradicts itself: its +1.5 V across V1A's 1500 Ohm cathode resistor is 1.0 mA, and 1.0 mA through the 100 kOhm plate load from the printed +280 V rail drops 100 V, leaving about 180 V at the plate. 135 V would take 1.45 mA, which would put 2.2 V on that cathode, not the printed 1.5 V. No reading of the sheet makes both figures true."
      },
      "KA": {
        "chart": 1.5,
        "tol_pct": 20,
        "note": "V1A cathode, over its own 1.5k/25uF"
      },
      "PB": {
        "chart": 135,
        "disputed": true,
        "dispute_note": "V1B (7025) plate, 100k off BD — the drawing prints +135 V at both 7025 plates, on both pages. Same contradiction as PA: +1.5 V across V1B's cathode (1500 Ohm, with the 56 kOhm feedback leg in parallel, 1461 Ohm together) is about 1.03 mA, and that through the 100 kOhm load from +280 V drops about 103 V, leaving about 177 V at the plate, not 135."
      },
      "KB": {
        "chart": 1.5,
        "tol_pct": 20,
        "note": "V1B cathode, over its unbypassed 1.5k — the 56k speaker feedback lands on this node, a second DC path to ground (the speaker line sits at ~0 V through the output transformer's secondary)"
      },
      "PPI": {
        "chart": 230,
        "tol_pct": 20,
        "note": "cathodyne plate, 56k load from BD"
      },
      "KPI": {
        "chart": 56.5,
        "tol_pct": 20,
        "note": "cathodyne cathode pin, above the 1k cathode resistor into the tail"
      },
      "JPI": {
        "chart": 55,
        "tol_pct": 20,
        "note": "cathodyne tail junction (1k cathode resistor / 56k-to-ground), grid-leak return"
      },
      "G61": {
        "chart": -35,
        "tol_pct": 8,
        "note": "6V6 (V3) grid — behind its 1500 ohm stopper and a 220k 5% leak from the -35 V bias line"
      },
      "G62": {
        "chart": -35,
        "tol_pct": 8,
        "note": "6V6 (V4) grid, the same stopper-and-leak wiring"
      }
    }
  },
  "operatingPoint": [
    {
      "node": "BS",
      "chart": 312,
      "sim": 311.938,
      "disputed": false,
      "dev_pct": 0.01987179487179866,
      "tol_pct": 8,
      "gated": true,
      "within": true,
      "note": "6V6 screen node, one 1000 Ohm-1W dropper below the driven reservoir — internal target, tighter than the drawing's own +/-20%",
      "dispute_note": ""
    },
    {
      "node": "BD",
      "chart": 280,
      "sim": 281.323,
      "disputed": false,
      "dev_pct": 0.47249999999999254,
      "tol_pct": 8,
      "gated": true,
      "within": true,
      "note": "preamp/PI rail, 10k-1W below the screen node — internal target",
      "dispute_note": ""
    },
    {
      "node": "PA",
      "chart": 135,
      "sim": 183.881,
      "disputed": true,
      "dev_pct": 36.20814814814815,
      "tol_pct": 5,
      "gated": false,
      "within": null,
      "note": "",
      "dispute_note": "V1A (7025) plate, 100k off BD. Both pages of H-FA print +135 V here, the 3 unambiguous on the 800 ppi layout copy. The chart contradicts itself: its +1.5 V across V1A's 1500 Ohm cathode resistor is 1.0 mA, and 1.0 mA through the 100 kOhm plate load from the printed +280 V rail drops 100 V, leaving about 180 V at the plate. 135 V would take 1.45 mA, which would put 2.2 V on that cathode, not the printed 1.5 V. No reading of the sheet makes both figures true."
    },
    {
      "node": "KA",
      "chart": 1.5,
      "sim": 1.462,
      "disputed": false,
      "dev_pct": 2.533333333333336,
      "tol_pct": 20,
      "gated": true,
      "within": true,
      "note": "V1A cathode, over its own 1.5k/25uF",
      "dispute_note": ""
    },
    {
      "node": "PB",
      "chart": 135,
      "sim": 182.688,
      "disputed": true,
      "dev_pct": 35.32444444444444,
      "tol_pct": 5,
      "gated": false,
      "within": null,
      "note": "",
      "dispute_note": "V1B (7025) plate, 100k off BD — the drawing prints +135 V at both 7025 plates, on both pages. Same contradiction as PA: +1.5 V across V1B's cathode (1500 Ohm, with the 56 kOhm feedback leg in parallel, 1461 Ohm together) is about 1.03 mA, and that through the 100 kOhm load from +280 V drops about 103 V, leaving about 177 V at the plate, not 135."
    },
    {
      "node": "KB",
      "chart": 1.5,
      "sim": 1.441,
      "disputed": false,
      "dev_pct": 3.9333333333333296,
      "tol_pct": 20,
      "gated": true,
      "within": true,
      "note": "V1B cathode, over its unbypassed 1.5k — the 56k speaker feedback lands on this node, a second DC path to ground (the speaker line sits at ~0 V through the output transformer's secondary)",
      "dispute_note": ""
    },
    {
      "node": "PPI",
      "chart": 230,
      "sim": 219.683,
      "disputed": false,
      "dev_pct": 4.485652173913047,
      "tol_pct": 20,
      "gated": true,
      "within": true,
      "note": "cathodyne plate, 56k load from BD",
      "dispute_note": ""
    },
    {
      "node": "KPI",
      "chart": 56.5,
      "sim": 62.741,
      "disputed": false,
      "dev_pct": 11.046017699115044,
      "tol_pct": 20,
      "gated": true,
      "within": true,
      "note": "cathodyne cathode pin, above the 1k cathode resistor into the tail",
      "dispute_note": ""
    },
    {
      "node": "JPI",
      "chart": 55,
      "sim": 61.64,
      "disputed": false,
      "dev_pct": 12.072727272727274,
      "tol_pct": 20,
      "gated": true,
      "within": true,
      "note": "cathodyne tail junction (1k cathode resistor / 56k-to-ground), grid-leak return",
      "dispute_note": ""
    },
    {
      "node": "G61",
      "chart": -35,
      "sim": -35,
      "disputed": false,
      "dev_pct": 0,
      "tol_pct": 8,
      "gated": true,
      "within": true,
      "note": "6V6 (V3) grid — behind its 1500 ohm stopper and a 220k 5% leak from the -35 V bias line",
      "dispute_note": ""
    },
    {
      "node": "G62",
      "chart": -35,
      "sim": -35,
      "disputed": false,
      "dev_pct": 0,
      "tol_pct": 8,
      "gated": true,
      "within": true,
      "note": "6V6 (V4) grid, the same stopper-and-leak wiring",
      "dispute_note": ""
    }
  ],
  "checks": [
    {
      "id": "dc",
      "title": "DC operating point",
      "status": "Verified",
      "summary": "9 reference nodes are within tolerance. Maintainer verification is recorded for 2026-08-08; changes since then are awaiting maintainer re-review.",
      "details": [
        "The circuit's facts (netlist, reference voltages, parts list, both drawings' connections, capacitor polarity marks and heater declarations) have changed since the maintainer's review, or no review fingerprint is on record yet. The badge stands on its date until the maintainer re-reviews.",
        "2 disputed nodes are excluded from the tolerance result; their reasoning is listed in the operating-point table.",
        "This compares simulated DC conditions with the cited reference. It does not test sound, physical construction or every part of the circuit."
      ],
      "tone": "checked"
    },
    {
      "id": "schematic",
      "title": "Schematic against DC model",
      "status": "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.",
        "4 sheet-only parts are explicitly excluded: R1, R2, RG1, RG2. Heaters and the pilot lamp are checked separately."
      ],
      "tone": "checked"
    },
    {
      "id": "heaters",
      "title": "Heater and filament wiring",
      "status": "Checked",
      "summary": "The declared heater circuits cover the drawing and pass their separate wiring check.",
      "details": [],
      "tone": "checked"
    },
    {
      "id": "polarity",
      "title": "Capacitor polarity",
      "status": "Partial",
      "summary": "1 capacitor marking cannot be confirmed by the DC model.",
      "details": [
        "CKTO: CKTO.a: reaches only ground, through RKTO"
      ],
      "tone": "attention"
    }
  ],
  "corrections": [
    {
      "id": "6g2-cathodyne-resistor-2026-10-03",
      "date": "2026-10-03",
      "amps": [
        "6g2"
      ],
      "title": "6G2 phase-inverter cathode resistor read as printed",
      "description": "The phase inverter's cathode resistor is now the 1 kΩ printed on the factory layout drawing. The previous 1.5 kΩ had been chosen to match the printed voltages rather than read from the drawing. The cathode and tail voltages now simulate 11–12 % above the chart, within the drawing's stated ±20 %.",
      "commit": "c4333b3599f1b39e0d9121ff32f93f5ff1dbe1d0",
      "url": "https://github.com/TheAnalogMaker/circuit-codex/commit/c4333b3599f1b39e0d9121ff32f93f5ff1dbe1d0"
    },
    {
      "id": "6g2-tone-pi-2026-10-03",
      "date": "2026-10-03",
      "amps": [
        "6g2"
      ],
      "title": "6G2 tone control, phase-inverter coupling and input leak",
      "description": "The tone control is now wired as the factory drawing shows, a blend between the volume control's input and wiper with its 0.005 µF capacitor to ground. A coupling capacitor the drawing does not show has been removed. The phase inverter's lower output is taken from its cathode, and the input leak hangs from input 1's tip. The bias rectifier's type is no longer stated, since the drawing does not print one.",
      "commit": "742d2d86d86d3dff2b7eb5fee9f6709d263a4d56",
      "url": "https://github.com/TheAnalogMaker/circuit-codex/commit/742d2d86d86d3dff2b7eb5fee9f6709d263a4d56"
    }
  ],
  "sourceDirectory": "https://github.com/TheAnalogMaker/circuit-codex/tree/ebddc3fd2cf887dca010bbe60487d7391ea6c052/amps/6g2"
}