{
  "format": "circuit-codex-reference",
  "version": 1,
  "id": "ga40",
  "url": "https://circuitcodex.com/amps/ga40/",
  "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": "ga40",
    "name_style": "Gibson GA-40 Les Paul-style",
    "family": "other",
    "era": {
      "start": 1956,
      "end": 1962
    },
    "wattage": 15,
    "tubes": [
      5879,
      5879,
      "6SQ7",
      "12AX7",
      "6V6GT",
      "6V6GT",
      "5Y3GT"
    ],
    "topology": {
      "rectifier": {
        "kind": "tube",
        "type": "5Y3GT"
      },
      "bias": "cathode",
      "phase_inverter": "paraphase",
      "tone_stack": "single-knob"
    },
    "lineage": {
      "derived_from": [],
      "influenced": []
    },
    "conventions": {
      "designators": "functional",
      "notation": "us"
    },
    "sources": [
      {
        "desc": "Gibson factory drawing, title block 'GA-40' at the upper right and the 'Les Paul' signature at the lower left — THIS is the revision documented here. Complement read from the drawing: two 5879 pentodes (Channel 1 and Channel 2, one bottle each), a 6SQ7 tremolo oscillator, a 12AX7 phase inverter, two 6V6GT and a 5Y3GT. Values read directly from the drawing: each channel fed by two jacks through their own 51 kΩ series resistors onto one grid with a single 1 MΩ leak at the jack end; channel 1 on a 100 kΩ plate load with a 750 kΩ screen dropper bypassed by 0.05 µF and a 3.3 kΩ cathode resistor bypassed by 20 µF, coupled out through 0.01 µF to a 1 MΩ volume control and on through 470 kΩ to the inverter grid; channel 2 on a 2.2 kΩ cathode resistor and a 510 kΩ plate load, its output through a five-section ladder of 0.005 µF series capacitors with 1 MΩ shunts to its own 1 MΩ volume and a 100 kΩ mixing resistor; 12AX7 paraphase inverter with 220 kΩ anode loads on both halves, ONE shared 1 kΩ cathode resistor bypassed by 20 µF, and a 470 kΩ / 7.5 kΩ divider taking the first output grid down to the second half's grid; 0.02 µF inverter-to-grid couplers, 470 kΩ leak on the second output grid, the divider itself on the first; a 0.005 µF capacitor and a 1 MΩ control from the first inverter anode to ground as the amplifier's only tone control; 6V6GT pair on ONE shared 200 Ω cathode resistor with a 20 µF bypass and no bias supply, screens taken straight off the supply node with no screen resistors; supply chain 20 µF reservoir → 3 H choke → 10 µF → 10 kΩ → inverter rail → 10 kΩ → 10 µF preamp rail; tremolo on a 6SQ7 phase-shift oscillator with 510 kΩ resistors in its anode chain, a 500 kΩ Frequency control and a 100 kΩ / 500 kΩ Depth network; mains side a polarity switch choosing which line leg a 0.02 µF capacitor grounds, an on/off switch in one leg and a 3 A fuse in the other, and a 6.3 V pilot lamp on the heater winding. The sheet also prints a VOLTAGE TABLE, transcribed in the operating-point section of this page. Not reproduced here; archived at Schematic Heaven's Gibson library and mirrored at el34world.",
        "url": "https://schematicheaven.net/gibsonamps/ga40.pdf"
      },
      {
        "desc": "The same Gibson GA-40 drawing mirrored in el34world's Gibson schematic folder — byte-identical to the Schematic Heaven copy, and the second archive this entry's reading can be checked against.",
        "url": "https://el34world.com/charts/Schematics/files/Gibson/Gibson_ga40.pdf"
      },
      {
        "desc": "Gibson factory drawing captioned 'GA40 1954' — the EARLIER circuit under the same model number, cited here only to fix what this entry is not. It is a different amplifier. Its own tube-location strip letters V1 6SJ7 'Mic Amp', V2 6SJ7 'Instr Amp', V3 6SJ7 'Driver', V4 6SN7 'Phase Inverter — Tremolo', V5 and V6 6V6GT 'Output', V7 6V6GT 'Tremolo' and V8 5V4G 'Rectifier'; it carries a printed component legend (R1–R39, C1–C20) and the transformer numbers T1 GA-40P and T2 Z3533. There is no 5879 and no 6SQ7 on it, and the tremolo modulator is a third 6V6GT rather than a triode. Recorded as a history-tier row on the Gibson GA family page.",
        "url": "https://schematicheaven.net/gibsonamps/ga40_2.pdf"
      },
      {
        "desc": "Published bench feature on a 1956 GA-40 Les Paul at Guitar.com — the complement corroboration and the wattage this entry records. It lists '2x 5879, 2x 6V6, 1x 5Y3' with a '6SQ7 triode' for the tremolo, credits the tremolo circuit to Seth Lover, puts the output at 'approximately 15 watts' from a cathode-biased 6V6 pair, dates this second-generation model to 1956 and 1957, names the controls as four input jacks with volume, volume, frequency, depth and treble/bass, and describes channel 2 as carrying a filter network of the Vox AC10/AC15 kind — which is the five-section 0.005 µF ladder on the drawing. It also records that Gibson built no fewer than five Les Paul GA-40 variants.",
        "url": "https://guitar.com/reviews/1956-gibson-ga-40/"
      },
      {
        "desc": "GuitarPlayer's 'Classic Gear: Gibson Les Paul GA-40 Amp' — the model chronology behind this entry's era bracket and the Gibson GA family page: the GA-40 Les Paul debuted in 1952 and 'remained in the catalog until late 1962 or early '63' when Les Paul's agreement with Gibson ended; the original configuration carried 'three octal 6SJ7s and one 6SN7'; the mid-to-late-1950s variant is the one with the 5879 pentode preamp.",
        "url": "https://www.guitarplayer.com/gear/classic-gear-gibson-les-paul-ga-40-amp"
      },
      {
        "desc": "Service thread on The Amp Garage discussing the GA-40 Les Paul schematics — the independent naming of the inverter and of the tremolo mechanism this entry reports. It records that the 1954–1956 amplifiers used 6SJ7 preamp tubes and a 6SN7 phase inverter while from 1956 they used 5879 preamp tubes and a 12AX7 phase inverter with a cathode-biased 6V6 pair; it calls the inverter an 'old fashioned basic paraphase phase splitter' and describes the tremolo as working by B+ and screen-voltage modulation of the pentode input tube, which is why channel 2's screen sits so far below channel 1's on the factory chart.",
        "url": "https://ampgarage.com/forum/viewtopic.php?t=27749"
      },
      {
        "desc": "Published restoration account of a GA-40 Les Paul by Greg Cutshaw — the one place this entry's supply-can complement is corroborated. It records the power-supply capacitors as '20/10/10/10 µF at 450 WVDC', the original 6SQ7 oscillator tube, a single tone control working treble to bass, the tone circuit sitting 'between the phase inverter and power amp tubes', and 15 W RMS output.",
        "url": "https://www.gregcutshaw.com/Gibson%20GA-40%20Amp/Gibson%20GA-40%20Amp.html"
      },
      {
        "desc": "RCA 6SQ7, 6SQ7-GT/G data sheet, Dec. 1 1943 (Duplex-Diode High-Mu Triode) — the basing the drawn 6SQ7 socket is wired to, and the reason its heater pins are not the octal power tube's. \"Basing Designation ... 8Q\" with the printed terminal list: pin 1 metal shell (base sleeve on the GT/G), 2 triode grid, 3 cathode, 4 and 5 diode plates, 6 triode plate, 7 and 8 HEATER. Heater 6.3 V, 0.3 A; triode µ=100; maximum plate voltage 300 V, and no plate-dissipation rating printed on either this sheet or the Tung-Sol one. Cross-checked against the Tung-Sol 6SQ7 / 6SQ7GT sheet, Dec. 1 1947. See the 6SQ7 reference page.",
        "url": "https://frank.pocnet.net/sheets/049/6/6SQ7.pdf"
      },
      {
        "desc": "RCA 5879 data sheet, Data 1, 3-61 (Sharp-Cutoff Pentode, 9-pin miniature, 'For Audio-Amplifier Applications Critical as to Microphonics, Leakage Noise, and Hum') — anchor for the new CC0 5879 tube model and for the ratings that make this a preamp valve and nothing else: pentode connection Va=250 V, Vg2=100 V, Vg1=-3 V → Ia=1.8 mA, Ig2=0.4 mA, gm=1000 µmho, rp=2 MΩ; design-maximum 1.25 W plate dissipation, 0.25 W screen input, 330 V plate and screen supply; basing 9AD with grid No.3 'connected to cathode at socket'. See the 5879 reference page for the model and its method.",
        "url": "https://frank.pocnet.net/sheets/049/5/5879.pdf"
      }
    ],
    "verification": {
      "status": "draft"
    },
    "added": "2026-08-30T00:00:00.000Z",
    "contributors": [
      "TheAnalogMaker"
    ],
    "sections": {
      "V2": "excluded — channel 2's 5879: its screen is fed through the tremolo's Depth network, and neither that network nor the channel-2 screen dropper resolves on the only published drawing of this revision",
      "V3": "excluded — the 6SQ7 tremolo oscillator: a running phase-shift oscillator has no static operating point; its plate load taps a driven rail"
    }
  },
  "parts": {
    "notes": "Capacitor values are open at DC and do not enter the operating-point netlist; they are listed for completeness, and the ones whose BOTH leads land on a named DC node are modelled anyway so the push-pull phase and the bypass placement are fixed in the data. The drawing prints no wattages and no tolerances anywhere, so the era's implied ½ W is stated for the small resistors and the shared output cathode resistor — a part passing 92 mA at 18.5 V, some 1.7 W — carries no rating this entry can cite. A published restoration of a GA-40 records the supply-can complement as 20/10/10/10 µF at 450 WVDC; three of those four are lettered below, and the fourth is most likely on the +280 inverter rail, where this reading places no can. The gap is left visible rather than filled.",
    "items": [
      {
        "ref": "V1",
        "part": "Tube",
        "value": "5879",
        "role": "Channel 1 preamp pentode"
      },
      {
        "ref": "V2",
        "part": "Tube",
        "value": "5879",
        "role": "Channel 2 preamp pentode — the tremolo-modulated channel (stage not lettered here; see the header)"
      },
      {
        "ref": "V3",
        "part": "Tube",
        "value": "6SQ7",
        "role": "Tremolo phase-shift oscillator (excluded from the netlist; network not lettered here)"
      },
      {
        "ref": "V4",
        "part": "Tube",
        "value": "12AX7",
        "role": "Paraphase phase inverter, both triodes"
      },
      {
        "ref": "V5",
        "part": "Tube",
        "value": "6V6GT",
        "role": "Output beam power tube"
      },
      {
        "ref": "V6",
        "part": "Tube",
        "value": "6V6GT",
        "role": "Output beam power tube"
      },
      {
        "ref": "V7",
        "part": "Rectifier tube",
        "value": "5Y3GT",
        "role": "Full-wave rectifier"
      },
      {
        "ref": "T1",
        "part": "Power transformer",
        "value": "Gibson (no number printed)",
        "role": "Mains transformer — centre-tapped HT winding, 5 V rectifier winding, 6.3 V heater winding. The drawing prints the windings and no part number"
      },
      {
        "ref": "T2",
        "part": "Output transformer",
        "value": "Gibson (no number printed)",
        "role": "Output transformer, centre-tapped primary; the centre tap is the post-choke supply node the screens also sit on"
      },
      {
        "ref": "L1",
        "part": "Choke",
        "value": "3 H",
        "role": "Smoothing choke between the reservoir and the screen/output-transformer node"
      },
      {
        "ref": "—",
        "part": "Jack socket",
        "value": "1/4 in",
        "role": "Channel 1 input, first jack (annotation only)"
      },
      {
        "ref": "—",
        "part": "Jack socket",
        "value": "1/4 in",
        "role": "Channel 1 input, second jack (annotation only)"
      },
      {
        "ref": "RIN1",
        "part": "Carbon comp resistor",
        "value": "51 kΩ · ½ W",
        "role": "Channel 1 first-jack series resistor into the grid"
      },
      {
        "ref": "RIN2",
        "part": "Carbon comp resistor",
        "value": "51 kΩ · ½ W",
        "role": "Channel 1 second-jack series resistor into the same grid"
      },
      {
        "ref": "RG1",
        "part": "Carbon comp resistor",
        "value": "1 MΩ · ½ W",
        "role": "Channel 1 grid leak — at the jack end, ahead of both 51 kΩ resistors"
      },
      {
        "ref": "RL1",
        "part": "Carbon comp resistor",
        "value": "100 kΩ · ½ W",
        "role": "Channel 1 plate load, off the +265 preamp rail"
      },
      {
        "ref": "RS1",
        "part": "Carbon comp resistor",
        "value": "750 kΩ · ½ W",
        "role": "Channel 1 screen dropper, +265 rail → screen grid — the resistor the factory chart's own arithmetic confirms to 749 kΩ"
      },
      {
        "ref": "CS1",
        "part": "Film capacitor",
        "value": "0.05 µF",
        "role": "Channel 1 screen bypass to ground"
      },
      {
        "ref": "RK1",
        "part": "Carbon comp resistor",
        "value": "3.3 kΩ · ½ W",
        "role": "Channel 1 cathode bias"
      },
      {
        "ref": "CK1",
        "part": "Electrolytic capacitor",
        "value": "20 µF",
        "role": "Channel 1 cathode bypass (no voltage rating printed)"
      },
      {
        "ref": "CV1",
        "part": "Coupling capacitor",
        "value": "0.01 µF",
        "role": "Channel 1 plate → volume coupler"
      },
      {
        "ref": "VR1",
        "part": "Potentiometer",
        "value": "1 MΩ",
        "role": "Channel 1 volume — the drawing prints no taper. It is wired the unusual way round: the coupler drives the WIPER and the mixing resistor leaves the top of the track, with the bottom end grounded. Channel 2's volume is wired identically"
      },
      {
        "ref": "RM1",
        "part": "Carbon comp resistor",
        "value": "470 kΩ · ½ W",
        "role": "Channel 1 mixing resistor, volume control → inverter grid. It leaves the TOP of the volume track, not the wiper: the drawing brings the 0.01 µF coupler onto the wiper instead (see VR1)"
      },
      {
        "ref": "RL4A",
        "part": "Carbon comp resistor",
        "value": "220 kΩ · ½ W",
        "role": "Inverter driver plate load, off the +280 rail"
      },
      {
        "ref": "RL4B",
        "part": "Carbon comp resistor",
        "value": "220 kΩ · ½ W",
        "role": "Inverter inverted-side plate load, off the same rail"
      },
      {
        "ref": "RK4",
        "part": "Carbon comp resistor",
        "value": "1 kΩ · ½ W",
        "role": "Inverter cathode bias — ONE resistor shared by both triodes"
      },
      {
        "ref": "CK4",
        "part": "Electrolytic capacitor",
        "value": "20 µF",
        "role": "Inverter cathode bypass (no voltage rating printed)"
      },
      {
        "ref": "RPA",
        "part": "Carbon comp resistor",
        "value": "470 kΩ · ½ W",
        "role": "Paraphase divider, upper leg — first output grid down to the inverted half's grid; doubles as that output grid's leak"
      },
      {
        "ref": "RPB",
        "part": "Carbon comp resistor",
        "value": "7.5 kΩ · ½ W",
        "role": "Paraphase divider, lower leg — the inverted half's grid down to ground. 7.5/477.5 is 1/63.7, which is what a 12AX7 on a 220 kΩ load gives back"
      },
      {
        "ref": "CT1",
        "part": "Film capacitor",
        "value": "0.005 µF",
        "role": "Tone capacitor, inverter driver anode → Tone control"
      },
      {
        "ref": "VR3",
        "part": "Potentiometer",
        "value": "1 MΩ",
        "role": "Tone — the amplifier's only tone control, working treble to bass, wired with its wiper to ground and sitting between the phase inverter and the output tubes"
      },
      {
        "ref": "CC1",
        "part": "Coupling capacitor",
        "value": "0.02 µF",
        "role": "Inverter driver anode → V5 grid"
      },
      {
        "ref": "CC2",
        "part": "Coupling capacitor",
        "value": "0.02 µF",
        "role": "Inverter inverted-side anode → V6 grid"
      },
      {
        "ref": "RGL6",
        "part": "Carbon comp resistor",
        "value": "470 kΩ · ½ W",
        "role": "V6 grid leak — the only one of the two that goes to ground"
      },
      {
        "ref": "RKO",
        "part": "Power resistor",
        "value": "200 Ω",
        "role": "SHARED 6V6GT cathode bias resistor — the whole bias arrangement for the pair, with no bias supply anywhere in the amp. The drawing prints no wattage"
      },
      {
        "ref": "CKO",
        "part": "Electrolytic capacitor",
        "value": "20 µF",
        "role": "6V6GT cathode bypass (no voltage rating printed)"
      },
      {
        "ref": "CF1",
        "part": "Electrolytic capacitor",
        "value": "20 µF",
        "role": "Reservoir can, ahead of the choke — the 5Y3GT cathode node the chart reads +315 V"
      },
      {
        "ref": "CF2",
        "part": "Electrolytic capacitor",
        "value": "10 µF",
        "role": "Post-choke smoothing — the +310 V node that is also the output-transformer centre tap and both 6V6GT screens"
      },
      {
        "ref": "RD1",
        "part": "Carbon comp resistor",
        "value": "10 kΩ · ½ W",
        "role": "+310 node → +280 inverter rail"
      },
      {
        "ref": "RD2",
        "part": "Carbon comp resistor",
        "value": "10 kΩ · ½ W",
        "role": "+280 inverter rail → +265 preamp rail"
      },
      {
        "ref": "CF3",
        "part": "Electrolytic capacitor",
        "value": "10 µF",
        "role": "+265 preamp rail smoothing"
      },
      {
        "ref": "—",
        "part": "Speaker",
        "value": "12 in",
        "role": "Single 12-inch speaker (annotation only). Published accounts of this revision name a Jensen P12Q; the drawing letters no make"
      },
      {
        "ref": "—",
        "part": "Film capacitor",
        "value": "0.02 µF",
        "role": "Mains-side capacitor to ground, selected onto one line leg or the other by the polarity switch (annotation only)"
      },
      {
        "ref": "—",
        "part": "Toggle switch",
        "value": "SPST",
        "role": "Mains on/off, marked SW on the drawing, in one line leg (annotation only)"
      },
      {
        "ref": "—",
        "part": "Fuse",
        "value": "3 A",
        "role": "Mains fuse, in the other line leg (annotation only)"
      },
      {
        "ref": "—",
        "part": "Toggle switch",
        "value": "SPDT",
        "role": "Polarity switch — the era's line-reverse arrangement, which chooses which mains leg the 0.02 µF capacitor grounds; drawn beside the 115–125 V 50–60 cycle mains legend (annotation only)"
      },
      {
        "ref": "—",
        "part": "Pilot lamp",
        "value": "6.3 V",
        "role": "Pilot lamp, marked P.L. across the 6.3 V heater winding (annotation only)"
      }
    ]
  },
  "publishedVoltages": {
    "source": "Gibson GA-40 factory drawing, printed VOLTAGE TABLE: 5Y3GT 300 VAC per plate with +315 at the cathode; 6V6GT +305 plate, +310 screen, +18.5 cathode, +310 B+; 12AX7 +135 at both plates, +1.25 cathode, +280 B+; 5879 channel 1 +175 plate, +95 screen, +4 cathode, +265 B+; 5879 channel 2 +130 plate, +32 screen, +1.45 cathode, +265 B+; 6SQ7 tremolo oscillator +130 plate, +1.45 cathode. Stated convention: voltages to chassis with a 20,000 ohms-per-volt meter, tremolo 'off' and depth 'min'. The link is under Sources.",
    "nodes": {
      "P1": {
        "chart": 175,
        "tol_pct": 20,
        "note": "channel-1 5879 anode, 100 kΩ load off the +265 rail. Reads low: see the honest residual above — the 5879 model's screen-current law is anchored at Vg2=100 V and this stage runs at +95 V on a 750 kΩ dropper"
      },
      "SG1": {
        "chart": 95,
        "tol_pct": 20,
        "note": "channel-1 5879 screen grid, fed through 750 kΩ and bypassed to ground by 0.05 µF — the node that sets a pentode's current, and the node the model misses"
      },
      "K1": {
        "chart": 4,
        "tol_pct": 20,
        "note": "channel-1 5879 cathode, 3.3 kΩ bypassed by 20 µF. The chart's own plate and screen currents over that resistor give +3.7 V, so the printed +4 V and the drawing's 3.3 kΩ agree; the simulated figure inherits the screen error above"
      },
      "P4A": {
        "chart": 135,
        "tol_pct": 20,
        "note": "phase-inverter anode, driver half — 220 kΩ load off the +280 rail. The chart prints one figure for both halves in its E(p1)/E(p2) columns"
      },
      "P4B": {
        "chart": 135,
        "tol_pct": 20,
        "note": "phase-inverter anode, inverted half — 220 kΩ load, the half whose grid hangs on the 470 kΩ/7.5 kΩ paraphase divider"
      },
      "K4": {
        "chart": 1.25,
        "tol_pct": 20,
        "note": "phase-inverter shared cathode over ONE 1 kΩ resistor (20 µF bypass) — both halves on it, which is why 1.25 V and not half that"
      },
      "KOUT": {
        "chart": 18.5,
        "tol_pct": 20,
        "note": "shared 6V6GT cathode over the single 200 Ω resistor (20 µF bypass) — the amp's entire bias arrangement, for both bottles, with no bias supply anywhere"
      },
      "NPARA": {
        "chart": null,
        "note": "informational — the paraphase tap itself, where the 470 kΩ from the first output grid meets the 7.5 kΩ to ground and drives the inverter's second grid. Idles at exactly 0 V: there is no grid-current model in the archive's first-generation tube fits"
      },
      "G5": {
        "chart": null,
        "note": "informational — first 6V6GT control grid, behind the 0.02 µF coupler; its DC return is the paraphase divider itself rather than a leak of its own"
      },
      "G6": {
        "chart": null,
        "note": "informational — second 6V6GT control grid, behind its own 0.02 µF coupler with a 470 kΩ leak to ground"
      },
      "NIN1": {
        "chart": null,
        "note": "informational — the channel-1 jack node, where the 1 MΩ leak meets both 51 kΩ input resistors. No grid current flows, so this node sets no operating point"
      }
    }
  },
  "operatingPoint": [
    {
      "node": "P1",
      "chart": 175,
      "sim": 133.679,
      "disputed": false,
      "dev_pct": 23.612,
      "tol_pct": 20,
      "gated": true,
      "within": false,
      "note": "channel-1 5879 anode, 100 kΩ load off the +265 rail. Reads low: see the honest residual above — the 5879 model's screen-current law is anchored at Vg2=100 V and this stage runs at +95 V on a 750 kΩ dropper",
      "dispute_note": ""
    },
    {
      "node": "SG1",
      "chart": 95,
      "sim": 130.112,
      "disputed": false,
      "dev_pct": 36.959999999999994,
      "tol_pct": 20,
      "gated": true,
      "within": false,
      "note": "channel-1 5879 screen grid, fed through 750 kΩ and bypassed to ground by 0.05 µF — the node that sets a pentode's current, and the node the model misses",
      "dispute_note": ""
    },
    {
      "node": "K1",
      "chart": 4,
      "sim": 4.927,
      "disputed": false,
      "dev_pct": 23.17499999999999,
      "tol_pct": 20,
      "gated": true,
      "within": false,
      "note": "channel-1 5879 cathode, 3.3 kΩ bypassed by 20 µF. The chart's own plate and screen currents over that resistor give +3.7 V, so the printed +4 V and the drawing's 3.3 kΩ agree; the simulated figure inherits the screen error above",
      "dispute_note": ""
    },
    {
      "node": "P4A",
      "chart": 135,
      "sim": 139.476,
      "disputed": false,
      "dev_pct": 3.315555555555555,
      "tol_pct": 20,
      "gated": true,
      "within": true,
      "note": "phase-inverter anode, driver half — 220 kΩ load off the +280 rail. The chart prints one figure for both halves in its E(p1)/E(p2) columns",
      "dispute_note": ""
    },
    {
      "node": "P4B",
      "chart": 135,
      "sim": 139.476,
      "disputed": false,
      "dev_pct": 3.315555555555555,
      "tol_pct": 20,
      "gated": true,
      "within": true,
      "note": "phase-inverter anode, inverted half — 220 kΩ load, the half whose grid hangs on the 470 kΩ/7.5 kΩ paraphase divider",
      "dispute_note": ""
    },
    {
      "node": "K4",
      "chart": 1.25,
      "sim": 1.277,
      "disputed": false,
      "dev_pct": 2.159999999999993,
      "tol_pct": 20,
      "gated": true,
      "within": true,
      "note": "phase-inverter shared cathode over ONE 1 kΩ resistor (20 µF bypass) — both halves on it, which is why 1.25 V and not half that",
      "dispute_note": ""
    },
    {
      "node": "KOUT",
      "chart": 18.5,
      "sim": 18.312,
      "disputed": false,
      "dev_pct": 1.0162162162162098,
      "tol_pct": 20,
      "gated": true,
      "within": true,
      "note": "shared 6V6GT cathode over the single 200 Ω resistor (20 µF bypass) — the amp's entire bias arrangement, for both bottles, with no bias supply anywhere",
      "dispute_note": ""
    },
    {
      "node": "NPARA",
      "chart": null,
      "sim": 0,
      "disputed": false,
      "dev_pct": null,
      "tol_pct": 5,
      "gated": false,
      "within": null,
      "note": "informational — the paraphase tap itself, where the 470 kΩ from the first output grid meets the 7.5 kΩ to ground and drives the inverter's second grid. Idles at exactly 0 V: there is no grid-current model in the archive's first-generation tube fits",
      "dispute_note": ""
    },
    {
      "node": "G5",
      "chart": null,
      "sim": 0,
      "disputed": false,
      "dev_pct": null,
      "tol_pct": 5,
      "gated": false,
      "within": null,
      "note": "informational — first 6V6GT control grid, behind the 0.02 µF coupler; its DC return is the paraphase divider itself rather than a leak of its own",
      "dispute_note": ""
    },
    {
      "node": "G6",
      "chart": null,
      "sim": 0,
      "disputed": false,
      "dev_pct": null,
      "tol_pct": 5,
      "gated": false,
      "within": null,
      "note": "informational — second 6V6GT control grid, behind its own 0.02 µF coupler with a 470 kΩ leak to ground",
      "dispute_note": ""
    },
    {
      "node": "NIN1",
      "chart": null,
      "sim": 0,
      "disputed": false,
      "dev_pct": null,
      "tol_pct": 5,
      "gated": false,
      "within": null,
      "note": "informational — the channel-1 jack node, where the 1 MΩ leak meets both 51 kΩ input resistors. No grid current flows, so this node sets no operating point",
      "dispute_note": ""
    }
  ],
  "checks": [
    {
      "id": "dc",
      "title": "DC operating point",
      "status": "Outside target",
      "summary": "3 of 7 reference nodes fall outside their stated tolerance.",
      "details": [
        "This compares simulated DC conditions with the cited reference. It does not test sound, physical construction or every part of the circuit."
      ],
      "tone": "attention"
    },
    {
      "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.",
        "0 sheet-only parts are explicitly excluded. 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 V4.",
        "Gibson published no board-layout sheet for the GA-40 and none was located; this board is derived from the factory circuit drawing, so no factory drawing can establish its heater legs."
      ],
      "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/ga40"
}