{
  "format": "circuit-codex-reference",
  "version": 1,
  "id": "6g6b",
  "url": "https://circuitcodex.com/amps/6g6b/",
  "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": "6g6b",
    "name_style": "Blonde Bassman-style",
    "family": "other",
    "era": {
      "start": 1963,
      "end": 1964
    },
    "wattage": 50,
    "tubes": [
      7025,
      7025,
      7025,
      7025,
      5881,
      5881
    ],
    "topology": {
      "rectifier": {
        "kind": "solid-state"
      },
      "bias": "fixed",
      "phase_inverter": "long-tailed-pair",
      "tone_stack": "per-channel-tb"
    },
    "lineage": {
      "derived_from": [],
      "influenced": [
        "aa864-bassman"
      ]
    },
    "conventions": {
      "designators": "functional"
    },
    "sources": [
      {
        "desc": "Fender 'Bassman' Model 6G6-B drawing (E-FB), two pages (board layout + schematic): every component value AND the printed voltage chart read directly from the published sheet, lug by lug at 750 dpi. Two full channels (Bass, Normal). Bass ch.: 68k/68k input stoppers and a 1M leak into V1A (2700 ohm cathode, 220k plate off the Bass row's +230 V lane, printed +135/+1.1 V); V1A's plate is DIRECT-COUPLED to V1B, a CATHODE FOLLOWER whose plate lead runs straight to the same +230 V lane with no plate-load resistor and whose 100k cathode load is the stage output, printed +136 V; that cathode drives a 1M/.00025/47k/10k/.25/.25 network into a 25k-L Bass pot, an 820 ohm foot and a 250k-L Volume pot. Normal ch.: V2A on a 1500 ohm cathode with a 100k plate load climbing to that channel's own +355 V lane, printed +230/+1.9 V, feeding the blackface ladder on a tapped Treble pot — 100k slope, .00025 into the 350k-70k-tap pot's hot lug, .1 from the slope foot to the tap, .05 from the slope foot to the Bass foot, 6800 foot to ground, .005 from the pot's cold lug to ground — with a 250k-A Bass rheostat and a 1M-A Volume pot into V2B (2700 ohm cathode, 220k plate off the same +355 V lane, +190/+1.8 V), then a 470k mixing resistor. The Bass Volume's wiper feeds a third 7025 that carries the Bass channel's later stages (100k plate off +230 V, +150 V and 1500 ohm/+1.2 V on the first section, +150 V and 1500 ohm/+1.3 V with .002 across the plate load on the second); the Bass channel's own 250k-A Treble control (its front-panel group reads Bass 25k-L / Treble 250k-A / Volume 250k-L) sits between the bottle's two sections, then a 470k into the mixing node where the Normal channel's 470k lands, and a .0005 uF coupler from that node into the phase inverter: 82k (hot) / 100k (cold) 5% plates off a +410 V lane, printed +300/+280 V, both 1M grid leaks to the tail junction, an 820 ohm shared-cathode resistor printed +30 V (cathodes) / +28 V (tail junction), and below that junction a 6800 ohm to the presence/feedback node, a 4700 ohm from there to ground, the 56k speaker-feedback resistor returning to the same node and a 25k-L PRESENCE pot bridging the 4700 ohm with a .1/200 cap on its wiper. Fixed-bias 5881 pair: 220k 5% leaks from -54 V; the plates hang on the output transformer's primary, whose centre tap takes the '+430 V.' lead (the +428 V printed at the plate leads is the primary's own resistance), and the two 470 ohm 1W screen stoppers come off node B, the +428 V node past the choke. Solid-state full-wave rectifier (two 3-diode series legs off a centre-tapped HT winding) — no rectifier tube. Supply chain: +430 V reservoir -> choke (TR2, 125C1A) -> node B (+428 V) -> 4700 ohm 1W -> +410 V -> 27k 1W -> +355 V (node C); a 56k 1W from node B with its own 20 uF/600 V filter feeds the Bass row's +230 V lane. Bias supply: small silicon diode + 1k 1W-5% off an AC tap, 27k-5% bleeder, 25/50 uF dual can, -54 V. Transformers TR1-125P7A (power), TR2-125C1A (choke), TR3-125A13A (output). Notice printed on the sheet: 'Voltages read to ground with electronic voltmeter, values shown + or - 20%'; 'All resistors 1/2 W-10% tolerance if not specified'; 'All capacitors at least 400 volt rating if not specified.' Not reproduced here; archived at EL34World",
        "url": "https://el34world.com/charts/Schematics/Files/Fender/Fender_bassman_6g6b.pdf"
      },
      {
        "desc": "Wikipedia, 'Fender Bassman' — 6G6-B production window and circuit lineage: 6G6 (late 1960, GZ34 tube rectifier) -> 6G6-A (early 1961, solid-state rectifier, 2x12 cabinet) -> 6G6-B (circuit changes carried through 1963); the blonde/piggyback Bassman line ran 1960-1964, superseded by the blackface AA864 piggyback head in 1964",
        "url": "https://en.wikipedia.org/wiki/Fender_Bassman"
      }
    ],
    "verification": {
      "status": "draft"
    },
    "added": "2026-08-08T00:00:00.000Z",
    "contributors": [
      "TheAnalogMaker"
    ]
  },
  "parts": {
    "notes": "Two full 4-pin input jacks per channel (2/1, hi/lo) share one 68 kΩ-per-jack, 1 MΩ-leak grid network, same convention as the tweed amps. Values keyed to the E-FB drawing, re-read from the source PDF at 750 dpi lug by lug. Every value in the signal and supply path is read from the sheet. V1B is a cathode follower, so it has no plate-load resistor, no interstage coupling cap and no grid leak of its own, and the phase-inverter tail's foot is lettered in full (6.8 kΩ, 4.7 kΩ, the 56 kΩ speaker feedback and the Presence pot across the foot). The only parts still marked (estimate) are three grid leaks the sheet does not draw as discrete resistors — RG2B, RG3A and RG3B stand in for a DC return the Volume and Treble pots above them already provide, and no stage's operating point turns on their value. Cathode-bypass electrolytics that the drawing shows as a shared dual-section can are drawn here as one equivalent cap per stage, valued as the chart prints the pair.",
    "items": [
      {
        "ref": "R1s",
        "part": "Carbon comp resistor",
        "value": "68 kΩ · ½ W",
        "role": "Bass ch. jack 2 stopper"
      },
      {
        "ref": "R2s",
        "part": "Carbon comp resistor",
        "value": "68 kΩ · ½ W",
        "role": "Bass ch. jack 1 stopper"
      },
      {
        "ref": "RG1A",
        "part": "Carbon comp resistor",
        "value": "1 MΩ · ½ W",
        "role": "Bass ch. input grid leak"
      },
      {
        "ref": "RL1A",
        "part": "Carbon comp resistor",
        "value": "220 kΩ · ½ W",
        "role": "V1A plate load, off the Bass row's +230 V lane; its bottom end is also V1B's grid"
      },
      {
        "ref": "RK1A",
        "part": "Carbon comp resistor",
        "value": "2.7 kΩ · ½ W",
        "role": "V1A cathode bias"
      },
      {
        "ref": "CK1A",
        "part": "Electrolytic capacitor",
        "value": "25 µF (dual-can pair)",
        "role": "V1A cathode bypass"
      },
      {
        "ref": "RK1B",
        "part": "Carbon comp resistor",
        "value": "100 kΩ · ½ W",
        "role": "V1B cathode-follower load to ground — the stage's output, feeding the Bass channel's tone network"
      },
      {
        "ref": "CTN1",
        "part": "Mica capacitor",
        "value": "250 pF (.00025 µF)",
        "role": "Bass ch. tone network: treble branch, off V1B's cathode, in series with RTN1 up to the Volume pot's top"
      },
      {
        "ref": "RTN1",
        "part": "Carbon comp resistor",
        "value": "47 kΩ · ½ W",
        "role": "Bass ch. tone network: treble branch slope, CTN1 to the Volume pot's top"
      },
      {
        "ref": "RTN2",
        "part": "Carbon comp resistor",
        "value": "1 MΩ · ½ W",
        "role": "Bass ch. tone network: off V1B's cathode down to the node both 0.25 µF caps share"
      },
      {
        "ref": "CTN2",
        "part": "Film capacitor",
        "value": "0.25 µF",
        "role": "Bass ch. tone network: from the 1M's foot to the Bass pot's wiper (the 10k's foot)"
      },
      {
        "ref": "CTN3",
        "part": "Film capacitor",
        "value": "0.25 µF",
        "role": "Bass ch. tone network: from the 1M's foot to the Bass pot's far lug (the 820's top)"
      },
      {
        "ref": "RTN3",
        "part": "Carbon comp resistor",
        "value": "10 kΩ · ½ W",
        "role": "Bass ch. tone network: from the Volume pot's top down to the Bass pot's wiper"
      },
      {
        "ref": "VR1",
        "part": "Linear potentiometer (rheostat)",
        "value": "25 kΩ-L",
        "role": "Bass ch. Bass control: a rheostat from the 10k's foot (wiper) to the 820 foot (far lug); its third lug is free on the layout page"
      },
      {
        "ref": "RBF",
        "part": "Carbon comp resistor",
        "value": "820 Ω · ½ W",
        "role": "Bass ch. tone-network foot, the Bass pot's far lug to ground; mounts at the Bass pot on the layout page"
      },
      {
        "ref": "VR2",
        "part": "Linear potentiometer",
        "value": "250 kΩ-L",
        "role": "Bass ch. Volume control; wiper feeds V3A's grid, the channel's next gain stage"
      },
      {
        "ref": "R3s",
        "part": "Carbon comp resistor",
        "value": "68 kΩ · ½ W",
        "role": "Normal ch. jack 2 stopper"
      },
      {
        "ref": "R4s",
        "part": "Carbon comp resistor",
        "value": "68 kΩ · ½ W",
        "role": "Normal ch. jack 1 stopper"
      },
      {
        "ref": "RG2A",
        "part": "Carbon comp resistor",
        "value": "1 MΩ · ½ W",
        "role": "Normal ch. input grid leak"
      },
      {
        "ref": "RL2A",
        "part": "Carbon comp resistor",
        "value": "100 kΩ · ½ W",
        "role": "V2A plate load, climbing to the Normal channel's +355 V lane"
      },
      {
        "ref": "RK2A",
        "part": "Carbon comp resistor",
        "value": "1.5 kΩ · ½ W",
        "role": "V2A cathode bias"
      },
      {
        "ref": "CK2A",
        "part": "Electrolytic capacitor",
        "value": "25 µF (dual-can pair)",
        "role": "V2A cathode bypass"
      },
      {
        "ref": "RTN5",
        "part": "Carbon comp resistor",
        "value": "100 kΩ · ½ W",
        "role": "Normal ch. tone network: slope resistor, V2A's plate to the slope foot"
      },
      {
        "ref": "CTN4",
        "part": "Mica capacitor",
        "value": "250 pF (.00025 µF)",
        "role": "Normal ch. tone network: treble capacitor, V2A's plate to the Treble pot's hot lug"
      },
      {
        "ref": "VR3",
        "part": "Audio-taper potentiometer (tapped)",
        "value": "350 kΩ, 70 kΩ tap",
        "role": "Normal ch. Treble control — a tapped pot with four connections: hot lug from CTN4, wiper to the Volume pot, the 70 kΩ tap carrying CTN7 from the slope foot (and the Bass pot's hot lug), cold lug bled to ground through CTN6"
      },
      {
        "ref": "CTN7",
        "part": "Film capacitor",
        "value": "0.1 µF",
        "role": "Normal ch. tone network: slope foot to the Treble pot's 70 kΩ tap — the ladder's bass-capacitor position"
      },
      {
        "ref": "CTN5",
        "part": "Film capacitor",
        "value": "0.05 µF",
        "role": "Normal ch. tone network: slope foot to the Bass pot's foot lug — the ladder's mid-capacitor position"
      },
      {
        "ref": "VR4",
        "part": "Audio-taper potentiometer (rheostat)",
        "value": "250 kΩ-A",
        "role": "Normal ch. Bass control, a rheostat from the Treble tap node down to the 6.8 kΩ foot; wiper strapped to its foot lug"
      },
      {
        "ref": "RTN4",
        "part": "Carbon comp resistor",
        "value": "6.8 kΩ · ½ W",
        "role": "Normal ch. tone-network foot, the Bass pot's foot lug to ground; mounts at the Bass pot on the layout page"
      },
      {
        "ref": "CTN6",
        "part": "Film capacitor",
        "value": "0.005 µF",
        "role": "Normal ch. tone network: the Treble pot's cold lug to ground; mounts at the Treble pot on the layout page"
      },
      {
        "ref": "VR5",
        "part": "Audio-taper potentiometer",
        "value": "1 MΩ-A",
        "role": "Normal ch. Volume control; top fed from the Treble wiper, wiper feeds V2B's grid"
      },
      {
        "ref": "RG2B",
        "part": "Carbon comp resistor",
        "value": "1 MΩ · ½ W (estimate)",
        "role": "V2B grid leak — return path off the Volume wiper"
      },
      {
        "ref": "RL2B",
        "part": "Carbon comp resistor",
        "value": "220 kΩ · ½ W",
        "role": "V2B plate load, off the same +355 V lane"
      },
      {
        "ref": "RK2B",
        "part": "Carbon comp resistor",
        "value": "2.7 kΩ · ½ W",
        "role": "V2B cathode bias"
      },
      {
        "ref": "CK2B",
        "part": "Electrolytic capacitor",
        "value": "25 µF (dual-can pair)",
        "role": "V2B cathode bypass"
      },
      {
        "ref": "RM1",
        "part": "Carbon comp resistor",
        "value": "470 kΩ · ½ W",
        "role": "Normal ch. mixing resistor, V2B's plate → the mixing node after V3B, which C1 couples into the phase inverter"
      },
      {
        "ref": "RG3A",
        "part": "Carbon comp resistor",
        "value": "1 MΩ · ½ W (estimate)",
        "role": "V3A grid leak, off the Bass Volume's wiper"
      },
      {
        "ref": "RL3A",
        "part": "Carbon comp resistor",
        "value": "100 kΩ · ½ W",
        "role": "V3A plate load"
      },
      {
        "ref": "RK3A",
        "part": "Carbon comp resistor",
        "value": "1.5 kΩ · ½ W",
        "role": "V3A cathode bias, bypassed"
      },
      {
        "ref": "CDR1",
        "part": "Film capacitor",
        "value": "0.1 µF",
        "role": "V3A plate coupling into the Bass ch. Treble control"
      },
      {
        "ref": "VR6",
        "part": "Audio-taper potentiometer",
        "value": "250 kΩ-A",
        "role": "Bass ch. Treble control — the front-panel BASS/TREBLE/VOLUME group ahead of the Bass jacks (25k-L/250k-A/250k-L) places it here, in V3's own signal path between V3A and V3B, rather than beside the channel's other two pots"
      },
      {
        "ref": "RG3B",
        "part": "Carbon comp resistor",
        "value": "1 MΩ · ½ W (estimate)",
        "role": "V3B grid leak"
      },
      {
        "ref": "RL3B",
        "part": "Carbon comp resistor",
        "value": "100 kΩ · ½ W",
        "role": "V3B plate load"
      },
      {
        "ref": "RK3B",
        "part": "Carbon comp resistor",
        "value": "1.5 kΩ · ½ W",
        "role": "V3B cathode bias"
      },
      {
        "ref": "RM2",
        "part": "Carbon comp resistor",
        "value": "470 kΩ · ½ W",
        "role": "Bass ch. mixing resistor, V3B's plate → the mixing node, where RM1 joins it"
      },
      {
        "ref": "C1",
        "part": "Mica capacitor",
        "value": "500 pF (.0005 µF)",
        "role": "Mixing node → V4A grid coupling"
      },
      {
        "ref": "RG4A",
        "part": "Carbon comp resistor",
        "value": "1 MΩ · ½ W",
        "role": "V4A grid leak, returned to the tail junction"
      },
      {
        "ref": "RL4A",
        "part": "Carbon comp resistor",
        "value": "82 kΩ · ½ W · 5%",
        "role": "V4A plate load (hot side)"
      },
      {
        "ref": "RG4B",
        "part": "Carbon comp resistor",
        "value": "1 MΩ · ½ W",
        "role": "V4B grid leak, returned to the tail junction"
      },
      {
        "ref": "RL4B",
        "part": "Carbon comp resistor",
        "value": "100 kΩ · ½ W · 5%",
        "role": "V4B plate load (cold side)"
      },
      {
        "ref": "RTAIL",
        "part": "Carbon comp resistor",
        "value": "820 Ω · ½ W",
        "role": "Phase-inverter shared-cathode resistor"
      },
      {
        "ref": "RT2",
        "part": "Carbon comp resistor",
        "value": "6.8 kΩ · ½ W",
        "role": "Phase-inverter tail: junction → the presence/feedback node"
      },
      {
        "ref": "RPF",
        "part": "Carbon comp resistor",
        "value": "4.7 kΩ · ½ W",
        "role": "Presence/feedback foot resistor, that node → ground"
      },
      {
        "ref": "RNFB",
        "part": "Carbon comp resistor",
        "value": "56 kΩ · 1 W",
        "role": "Negative feedback, speaker line → the presence/feedback node (a second DC path to ground through the OT secondary)"
      },
      {
        "ref": "VR7",
        "part": "Linear potentiometer",
        "value": "25 kΩ-L",
        "role": "Presence control (front panel), its element bridging RPF end to end and its wiper feeding a 0.1 µF · 200 V cap to the foot"
      },
      {
        "ref": "RGL5",
        "part": "Carbon comp resistor",
        "value": "220 kΩ · ½ W",
        "role": "V5 grid leak, from the -54 V bias line"
      },
      {
        "ref": "RS5",
        "part": "Carbon comp resistor",
        "value": "470 Ω · 1 W",
        "role": "V5 screen stopper, off node B (+428 V)"
      },
      {
        "ref": "C2",
        "part": "Coupling capacitor",
        "value": "0.1 µF · 400 V",
        "role": "V4A → V5 grid"
      },
      {
        "ref": "RGL6",
        "part": "Carbon comp resistor",
        "value": "220 kΩ · ½ W",
        "role": "V6 grid leak, from the -54 V bias line"
      },
      {
        "ref": "RS6",
        "part": "Carbon comp resistor",
        "value": "470 Ω · 1 W",
        "role": "V6 screen stopper, off node B (+428 V)"
      },
      {
        "ref": "C3",
        "part": "Coupling capacitor",
        "value": "0.1 µF · 400 V",
        "role": "V4B → V6 grid"
      },
      {
        "ref": "DR1",
        "part": "Silicon rectifier diode",
        "value": "silicon diode",
        "role": "Main B+ rectifier bridge, series leg A, upper — HT_A leg, no rectifier tube"
      },
      {
        "ref": "DR2",
        "part": "Silicon rectifier diode",
        "value": "silicon diode",
        "role": "Main B+ rectifier bridge, series leg A, middle — HT_A leg"
      },
      {
        "ref": "DR3",
        "part": "Silicon rectifier diode",
        "value": "silicon diode",
        "role": "Main B+ rectifier bridge, series leg A, lower — HT_A leg"
      },
      {
        "ref": "DR4",
        "part": "Silicon rectifier diode",
        "value": "silicon diode",
        "role": "Main B+ rectifier bridge, series leg B, upper — HT_B leg"
      },
      {
        "ref": "DR5",
        "part": "Silicon rectifier diode",
        "value": "silicon diode",
        "role": "Main B+ rectifier bridge, series leg B, middle — HT_B leg"
      },
      {
        "ref": "DR6",
        "part": "Silicon rectifier diode",
        "value": "silicon diode",
        "role": "Main B+ rectifier bridge, series leg B, lower — HT_B leg"
      },
      {
        "ref": "C10",
        "part": "Electrolytic capacitor",
        "value": "20 µF · 600 V (×2, in parallel)",
        "role": "Filter, reservoir — the +430 V node, which the standby switch also carries up to the output transformer's primary centre tap"
      },
      {
        "ref": "C11",
        "part": "Electrolytic capacitor",
        "value": "20 µF · 600 V",
        "role": "Filter, node B: the post-choke +428 V node that feeds the two 5881 screen stoppers and the whole dropper chain"
      },
      {
        "ref": "C12",
        "part": "Electrolytic capacitor",
        "value": "20 µF · 600 V",
        "role": "Filter, the phase inverter's +410 V lane"
      },
      {
        "ref": "C15",
        "part": "Electrolytic capacitor",
        "value": "20 µF · 600 V",
        "role": "Filter, node C: the Normal channel's +355 V lane"
      },
      {
        "ref": "RD1",
        "part": "Power resistor",
        "value": "4.7 kΩ · 1 W",
        "role": "Rail dropper, node B (+428 V) → the phase inverter's +410 V lane"
      },
      {
        "ref": "RD2",
        "part": "Power resistor",
        "value": "27 kΩ · 1 W",
        "role": "Rail dropper, +410 V → the Normal channel's +355 V lane"
      },
      {
        "ref": "RD3",
        "part": "Power resistor",
        "value": "56 kΩ · 1 W",
        "role": "Rail dropper, the post-choke +428 V node → the Bass row's +230 V lane"
      },
      {
        "ref": "C14",
        "part": "Electrolytic capacitor",
        "value": "20 µF · 600 V",
        "role": "Filter, Bass-row +230 V lane"
      },
      {
        "ref": "L1",
        "part": "Filter choke",
        "value": "Fender 125C1A (TR2)",
        "role": "B+ filtering — between the +430 V reservoir and node B, the +428 V node that feeds the screens and the droppers"
      },
      {
        "ref": "DB1",
        "part": "Rectifier (bias)",
        "value": "silicon diode",
        "role": "Bias supply rectifier, AC tap"
      },
      {
        "ref": "RB1",
        "part": "Carbon comp resistor",
        "value": "1 kΩ · 1 W · 5%",
        "role": "Bias supply series resistor"
      },
      {
        "ref": "RB2",
        "part": "Carbon comp resistor",
        "value": "27 kΩ · 1 W · 5%",
        "role": "Bias supply bleeder"
      },
      {
        "ref": "C13",
        "part": "Electrolytic capacitor",
        "value": "25 µF + 50 µF",
        "role": "Bias supply filter — one dual-section can"
      },
      {
        "ref": "V1",
        "part": "Preamp tube",
        "value": "7025 (12AX7-family)",
        "role": "Bass channel, both stages (V1A/V1B)"
      },
      {
        "ref": "V2",
        "part": "Preamp tube",
        "value": "7025 (12AX7-family)",
        "role": "Normal channel, both stages (V2A/V2B)"
      },
      {
        "ref": "V3",
        "part": "Preamp tube",
        "value": "7025 (12AX7-family)",
        "role": "Bass channel, second and third gain stages (V3A/V3B), the channel's Treble control between them"
      },
      {
        "ref": "V4",
        "part": "Preamp tube",
        "value": "7025 (12AX7-family)",
        "role": "Long-tailed-pair phase inverter (V4A/V4B)"
      },
      {
        "ref": "V5",
        "part": "Power tube",
        "value": "5881",
        "role": "Push-pull output (upper)"
      },
      {
        "ref": "V6",
        "part": "Power tube",
        "value": "5881",
        "role": "Push-pull output (lower)"
      },
      {
        "ref": "T3",
        "part": "Output transformer",
        "value": "Fender 125A13A",
        "role": "Push-pull output"
      },
      {
        "ref": "T1",
        "part": "Power transformer",
        "value": "Fender 125P7A (TR1)",
        "role": "HT + heaters, centre-tapped HT winding for the solid-state bridge"
      }
    ]
  },
  "publishedVoltages": {
    "source": "Fender 'Bassman' Model 6G6-B drawing (E-FB), schematic page 2 (https://el34world.com/charts/Schematics/Files/Fender/Fender_bassman_6g6b.pdf), printed voltages: +430 (reservoir, and the output-transformer primary centre tap the 5881 plates hang on), +428 (node B, past the choke: the 5881 screen stoppers and the dropper chain), +410 (phase-inverter plate lane), +355 (Normal-ch. B+ lane), +230 (Bass-row B+ lane, lettered twice), -54 (fixed bias); tube pins +135/+1.1 (V1A plate/cathode), +136 (V1B cathode-follower output, 100k load), +230/+1.9 (V2A plate/cathode), +190/+1.8 (V2B plate/cathode), +150/+1.2 (V3A plate/cathode), +150/+1.3 (V3B plate/cathode), +300 (V4A plate, 82k), +280 (V4B plate, 100k), +30/+28 (phase-inverter shared cathode / tail junction, either side of the 820 Ohm)",
    "nodes": {
      "BP428": {
        "chart": 428,
        "tol_pct": 8,
        "note": "node B, the choke's far end — driven directly. It feeds the two 470 Ω screen stoppers and every dropper below"
      },
      "BP430": {
        "chart": 430,
        "tol_pct": 8,
        "note": "the reservoir, and (past the omitted standby switch) the output transformer's primary centre tap — driven directly, so the 5881 plates sit on it with the primary DCR omitted. The sheet's printed +428 V at the plate leads IS that omitted DCR, 2 V under the +430 V it letters at the tap"
      },
      "BP410": {
        "chart": 410,
        "tol_pct": 8,
        "note": "phase-inverter plate lane — derived from node B through the printed 4.7 kΩ · 1 W dropper; checked against the chart, not an input to it"
      },
      "BP355": {
        "chart": 355,
        "tol_pct": 8,
        "note": "Normal-channel B+ lane, node C — derived from +410 V through the printed 27 kΩ · 1 W dropper; feeds BOTH that channel's plate loads (V2A's 100 kΩ and V2B's 220 kΩ)"
      },
      "BP230": {
        "chart": 230,
        "tol_pct": 8,
        "note": "Bass-row B+ lane — lettered twice on that lane, and derived from node B (the post-choke +428 V node) through the printed 56 kΩ · 1 W dropper"
      },
      "P1A": {
        "chart": 135,
        "tol_pct": 20,
        "note": "Bass ch. V1A (input) plate, 220 kΩ off BP230 — also V1B's grid, which it drives directly"
      },
      "K1A": {
        "chart": 1.1,
        "tol_pct": 20,
        "note": "Bass ch. V1A cathode, 2700 Ω"
      },
      "K1B": {
        "chart": 136,
        "tol_pct": 20,
        "note": "Bass ch. V1B cathode-follower output: 100 kΩ load to ground, plate straight on BP230, grid taken directly off P1A. The follower rides about a volt above the plate that drives it, so the printed +136 V beside the printed +135 V is the drawing agreeing with itself; 136 V over 100 kΩ is the 1.36 mA that also closes the 56 kΩ rail dropper's arithmetic (see the circuit story)"
      },
      "P2A": {
        "chart": 230,
        "tol_pct": 20,
        "note": "Normal ch. V2A plate, 100 kΩ climbing to BP355 — the sheet's third '+230 V.' reading, a plate voltage and not a rail. The 125 V across that 100 kΩ is the same 1.25 mA the printed 1.9 V over 1500 Ω implies"
      },
      "K2A": {
        "chart": 1.9,
        "tol_pct": 20,
        "note": "Normal ch. V2A (input) cathode, 1500 Ω"
      },
      "P2B": {
        "chart": 190,
        "tol_pct": 20,
        "note": "Normal ch. V2B (recovery) plate, 220 kΩ off BP355; also one end of the 470 kΩ pair into the mixing node"
      },
      "K2B": {
        "chart": 1.8,
        "tol_pct": 20,
        "note": "Normal ch. V2B cathode, 2700 Ω"
      },
      "P3A": {
        "chart": 150,
        "tol_pct": 20,
        "note": "Bass ch. V3A plate, 100 kΩ off BP230"
      },
      "K3A": {
        "chart": 1.2,
        "tol_pct": 20,
        "note": "Bass ch. V3A cathode, 1500 Ω (bypassed) — printed on the sheet beside the stage, not mirrored"
      },
      "P3B": {
        "chart": 150,
        "tol_pct": 20,
        "note": "Bass ch. V3B (post-Treble) plate, 100 kΩ off BP230; also one end of the 470 kΩ pair into the mixing node"
      },
      "K3B": {
        "chart": 1.3,
        "tol_pct": 20,
        "note": "Bass ch. V3B cathode, 1500 Ω"
      },
      "P4A": {
        "chart": 300,
        "tol_pct": 20,
        "note": "phase-inverter plate, 82 kΩ (hot) side off BP410"
      },
      "P4B": {
        "chart": 280,
        "tol_pct": 20,
        "note": "phase-inverter plate, 100 kΩ (cold) side off BP410"
      },
      "KPI": {
        "chart": 30,
        "tol_pct": 20,
        "note": "phase-inverter joined cathodes, above the 820 Ω"
      },
      "JPI": {
        "chart": 28,
        "tol_pct": 20,
        "note": "phase-inverter tail junction, below the 820 Ω — grid-leak return for both halves, and the top of the drawn foot (6800 Ω to the feedback node, 4700 Ω from there to ground, the 56 kΩ speaker feedback a second path to ground at the same node)"
      },
      "G5": {
        "chart": -54,
        "tol_pct": 8,
        "note": "5881 (V5) grid, fixed bias through a 220 kΩ leak from the -54 V supply"
      }
    }
  },
  "operatingPoint": [
    {
      "node": "BP428",
      "chart": 428,
      "sim": 428,
      "disputed": false,
      "dev_pct": 0,
      "tol_pct": 8,
      "gated": true,
      "within": true,
      "note": "node B, the choke's far end — driven directly. It feeds the two 470 Ω screen stoppers and every dropper below",
      "dispute_note": ""
    },
    {
      "node": "BP430",
      "chart": 430,
      "sim": 430,
      "disputed": false,
      "dev_pct": 0,
      "tol_pct": 8,
      "gated": true,
      "within": true,
      "note": "the reservoir, and (past the omitted standby switch) the output transformer's primary centre tap — driven directly, so the 5881 plates sit on it with the primary DCR omitted. The sheet's printed +428 V at the plate leads IS that omitted DCR, 2 V under the +430 V it letters at the tap",
      "dispute_note": ""
    },
    {
      "node": "BP410",
      "chart": 410,
      "sim": 407.017,
      "disputed": false,
      "dev_pct": 0.7275609756097571,
      "tol_pct": 8,
      "gated": true,
      "within": true,
      "note": "phase-inverter plate lane — derived from node B through the printed 4.7 kΩ · 1 W dropper; checked against the chart, not an input to it",
      "dispute_note": ""
    },
    {
      "node": "BP355",
      "chart": 355,
      "sim": 354.968,
      "disputed": false,
      "dev_pct": 0.009014084507037258,
      "tol_pct": 8,
      "gated": true,
      "within": true,
      "note": "Normal-channel B+ lane, node C — derived from +410 V through the printed 27 kΩ · 1 W dropper; feeds BOTH that channel's plate loads (V2A's 100 kΩ and V2B's 220 kΩ)",
      "dispute_note": ""
    },
    {
      "node": "BP230",
      "chart": 230,
      "sim": 236.523,
      "disputed": false,
      "dev_pct": 2.8360869565217373,
      "tol_pct": 8,
      "gated": true,
      "within": true,
      "note": "Bass-row B+ lane — lettered twice on that lane, and derived from node B (the post-choke +428 V node) through the printed 56 kΩ · 1 W dropper",
      "dispute_note": ""
    },
    {
      "node": "P1A",
      "chart": 135,
      "sim": 128.924,
      "disputed": false,
      "dev_pct": 4.500740740740736,
      "tol_pct": 20,
      "gated": true,
      "within": true,
      "note": "Bass ch. V1A (input) plate, 220 kΩ off BP230 — also V1B's grid, which it drives directly",
      "dispute_note": ""
    },
    {
      "node": "K1A",
      "chart": 1.1,
      "sim": 1.321,
      "disputed": false,
      "dev_pct": 20.090909090909076,
      "tol_pct": 20,
      "gated": true,
      "within": false,
      "note": "Bass ch. V1A cathode, 2700 Ω",
      "dispute_note": ""
    },
    {
      "node": "K1B",
      "chart": 136,
      "sim": 129.24,
      "disputed": false,
      "dev_pct": 4.970588235294111,
      "tol_pct": 20,
      "gated": true,
      "within": true,
      "note": "Bass ch. V1B cathode-follower output: 100 kΩ load to ground, plate straight on BP230, grid taken directly off P1A. The follower rides about a volt above the plate that drives it, so the printed +136 V beside the printed +135 V is the drawing agreeing with itself; 136 V over 100 kΩ is the 1.36 mA that also closes the 56 kΩ rail dropper's arithmetic (see the circuit story)",
      "dispute_note": ""
    },
    {
      "node": "P2A",
      "chart": 230,
      "sim": 234.055,
      "disputed": false,
      "dev_pct": 1.7630434782608724,
      "tol_pct": 20,
      "gated": true,
      "within": true,
      "note": "Normal ch. V2A plate, 100 kΩ climbing to BP355 — the sheet's third '+230 V.' reading, a plate voltage and not a rail. The 125 V across that 100 kΩ is the same 1.25 mA the printed 1.9 V over 1500 Ω implies",
      "dispute_note": ""
    },
    {
      "node": "K2A",
      "chart": 1.9,
      "sim": 1.814,
      "disputed": false,
      "dev_pct": 4.526315789473677,
      "tol_pct": 20,
      "gated": true,
      "within": true,
      "note": "Normal ch. V2A (input) cathode, 1500 Ω",
      "dispute_note": ""
    },
    {
      "node": "P2B",
      "chart": 190,
      "sim": 196.871,
      "disputed": false,
      "dev_pct": 3.616315789473689,
      "tol_pct": 20,
      "gated": true,
      "within": true,
      "note": "Normal ch. V2B (recovery) plate, 220 kΩ off BP355; also one end of the 470 kΩ pair into the mixing node",
      "dispute_note": ""
    },
    {
      "node": "K2B",
      "chart": 1.8,
      "sim": 1.823,
      "disputed": false,
      "dev_pct": 1.2777777777777726,
      "tol_pct": 20,
      "gated": true,
      "within": true,
      "note": "Normal ch. V2B cathode, 2700 Ω",
      "dispute_note": ""
    },
    {
      "node": "P3A",
      "chart": 150,
      "sim": 153.148,
      "disputed": false,
      "dev_pct": 2.098666666666664,
      "tol_pct": 20,
      "gated": true,
      "within": true,
      "note": "Bass ch. V3A plate, 100 kΩ off BP230",
      "dispute_note": ""
    },
    {
      "node": "K3A",
      "chart": 1.2,
      "sim": 1.251,
      "disputed": false,
      "dev_pct": 4.249999999999995,
      "tol_pct": 20,
      "gated": true,
      "within": true,
      "note": "Bass ch. V3A cathode, 1500 Ω (bypassed) — printed on the sheet beside the stage, not mirrored",
      "dispute_note": ""
    },
    {
      "node": "P3B",
      "chart": 150,
      "sim": 156.125,
      "disputed": false,
      "dev_pct": 4.083333333333333,
      "tol_pct": 20,
      "gated": true,
      "within": true,
      "note": "Bass ch. V3B (post-Treble) plate, 100 kΩ off BP230; also one end of the 470 kΩ pair into the mixing node",
      "dispute_note": ""
    },
    {
      "node": "K3B",
      "chart": 1.3,
      "sim": 1.271,
      "disputed": false,
      "dev_pct": 2.2307692307692415,
      "tol_pct": 20,
      "gated": true,
      "within": true,
      "note": "Bass ch. V3B cathode, 1500 Ω",
      "dispute_note": ""
    },
    {
      "node": "P4A",
      "chart": 300,
      "sim": 296.794,
      "disputed": false,
      "dev_pct": 1.0686666666666724,
      "tol_pct": 20,
      "gated": true,
      "within": true,
      "note": "phase-inverter plate, 82 kΩ (hot) side off BP410",
      "dispute_note": ""
    },
    {
      "node": "P4B",
      "chart": 280,
      "sim": 287.756,
      "disputed": false,
      "dev_pct": 2.76999999999999,
      "tol_pct": 20,
      "gated": true,
      "within": true,
      "note": "phase-inverter plate, 100 kΩ (cold) side off BP410",
      "dispute_note": ""
    },
    {
      "node": "KPI",
      "chart": 30,
      "sim": 30.33,
      "disputed": false,
      "dev_pct": 1.0999999999999943,
      "tol_pct": 20,
      "gated": true,
      "within": true,
      "note": "phase-inverter joined cathodes, above the 820 Ω",
      "dispute_note": ""
    },
    {
      "node": "JPI",
      "chart": 28,
      "sim": 28.25,
      "disputed": false,
      "dev_pct": 0.8928571428571428,
      "tol_pct": 20,
      "gated": true,
      "within": true,
      "note": "phase-inverter tail junction, below the 820 Ω — grid-leak return for both halves, and the top of the drawn foot (6800 Ω to the feedback node, 4700 Ω from there to ground, the 56 kΩ speaker feedback a second path to ground at the same node)",
      "dispute_note": ""
    },
    {
      "node": "G5",
      "chart": -54,
      "sim": -54,
      "disputed": false,
      "dev_pct": 0,
      "tol_pct": 8,
      "gated": true,
      "within": true,
      "note": "5881 (V5) grid, fixed bias through a 220 kΩ leak from the -54 V supply",
      "dispute_note": ""
    }
  ],
  "checks": [
    {
      "id": "dc",
      "title": "DC operating point",
      "status": "Outside target",
      "summary": "1 of 21 reference nodes falls outside its 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.",
        "9 sheet-only parts are explicitly excluded: C10, C11, C12, C14, C15, L1, RD1, RD2, RD3. 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, V4.",
        "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": "4 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": [
    {
      "id": "6g6b-supply-2026-09-18",
      "date": "2026-09-18",
      "amps": [
        "6g6b"
      ],
      "title": "6G6-B supply chain and output-stage feeds",
      "description": "The supply droppers follow the factory drawing's order. The output plates use the reservoir supply and the screens use the node after the choke; those feeds had been interchanged. The circuit remains a draft.",
      "commit": "df21e09",
      "url": "https://github.com/TheAnalogMaker/circuit-codex/commit/df21e09"
    }
  ],
  "sourceDirectory": "https://github.com/TheAnalogMaker/circuit-codex/tree/ebddc3fd2cf887dca010bbe60487d7391ea6c052/amps/6g6b"
}