{
  "format": "circuit-codex-reference",
  "version": 1,
  "id": "ab165",
  "url": "https://circuitcodex.com/amps/ab165/",
  "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": "ab165",
    "name_style": "Blackface Bassman-style",
    "family": "blackface",
    "era": {
      "start": 1965,
      "end": 1967
    },
    "wattage": 50,
    "tubes": [
      "12AX7",
      "12AX7",
      "12AX7",
      "12AT7",
      "6L6GC",
      "6L6GC"
    ],
    "topology": {
      "rectifier": {
        "kind": "solid-state",
        "type": "silicon full-wave"
      },
      "bias": "fixed",
      "phase_inverter": "long-tailed-pair",
      "tone_stack": "tb"
    },
    "lineage": {
      "derived_from": [
        "aa864-bassman"
      ],
      "influenced": []
    },
    "conventions": {
      "designators": "functional"
    },
    "sources": [
      {
        "desc": "Fender 'Bassman-Amp AB165' drawing (D-FE), title block read directly: 'FENDER MODEL \"BASSMAN-AMP AB165\"'. Every component value AND the printed voltage chart read from the published sheet. Complement three 7025 preamp bottles (a 12AX7 alias), one 12AT7 phase inverter, two 6L6GC, solid-state rectification (three series silicon diodes per leg off a 320-0-320 V winding). Bass and Normal channels each: two 68k input stoppers, with the 1M leak at jack 1's tip (jack side of its stopper), 100k plate load, 1.5k/25-25 cathode; two-knob tone stack (100k slope, 250k-A treble and bass, treble-wiper output) on a 1M-A volume; a second 7025 stage on 100k/1.5k. Bass channel adds a 0.01 uF shunt across its input-stage plate load, a 330 pF treble cap, an 8.2k tone-stack foot and a DEEP switch on a 0.1 uF; Normal channel a 250 pF treble cap, a 0.047 uF middle-leg cap, a 6.8k foot and a BRIGHT switch on 120 pF. Both second-stage plates reach a shared mixing node through 220k each; the mixer/driver 7025 (100k plate, 1.5k cathode, 470k grid leak) is returned to that node through 470k and coupled into it by 0.01 uF. 12AT7 long-tailed pair, both plate loads 100k 5% off +415 with 1M grid leaks to the tail junction, 470 Ohm to a 22k tail bypassed by 0.1-200, and a 220k from EACH plate back to the output plate rail. 6L6GC pair fixed-biased at -45 V through 220k-5% leaks and 1500 Ohm stoppers, 0.022 couplers, 470 Ohm-1W screens, grounded cathodes. 47k + 0.1 uF negative feedback from the speaker line to the inverter's hot grid. Rails +425/+415/+390/+320 on 70-350 (x2, with 220k-1W balancing), 20-525 (x3) and 8-450 cans through 1k-1W, 4.7k-1W and 27k-1W droppers, with the choke between the reservoir and the screen node and a standby switch ahead of it, the output transformer's centre tap on the reservoir side of the choke; bias supply 470 Ohm-1W + silicon diode + one filter capacitor (value lettered only on the layout page, 50 uF / 50 V) + a 10 kOhm-L BIAS BALANCE control across the bias node and a 15k foot, a 10k leg from each of its ends to one junction; V5's grid leak returns to the wiper (-45 V), V6's to that junction. Transformers TR1 125P7D (125P7DX export), TR2 125C1A choke, TR3 125A13A output. Notice: values +/-20 %, read to ground with an electronic voltmeter; all resistors 1/2 W 10 % and all capacitors at least 400 V unless specified; 'when installing new 6L6's reset hum balance for min hum'. Not reproduced here; archived at EL34World",
        "url": "https://el34world.com/charts/Schematics/files/Fender/Fender_bassman_ab165.pdf"
      },
      {
        "desc": "Wikipedia, 'Fender Bassman' — the AB165 dates and the 50 W rating. The AB165 drawing itself carries no date and prints no power rating; the circuit is placed c. 1965 and carried into the early silverface (drip-edge) period, on the 50 W blackface piggyback chassis the AA864 introduced in 1964",
        "url": "https://en.wikipedia.org/wiki/Fender_Bassman"
      },
      {
        "desc": "Fender 'Bassman-Amp AB165' LAYOUT drawing (D-FE), title block read directly: 'FENDER MODEL \"BASSMAN-AMP AB165\" LAYOUT'. One 2148 x 1578 page at 200 ppi. Read 2026-10-03 (V1 audit): the bias board carries one electrolytic, lettered '50 | 50' with + and - (the CB1 value the schematic does not print); the 15K and the two 10K legs at the 10K-L BIAS BALANCE control as the schematic draws them; the Bass channel's treble cap lettered 330 on the board. Not reproduced here; archived at EL34World.",
        "url": "https://el34world.com/charts/Schematics/Files/Fender/Fender_bassman_ab165_layout.pdf"
      }
    ],
    "verification": {
      "status": "verified",
      "date": "2026-08-08T00:00:00.000Z",
      "max_deviation_pct": 19.7
    },
    "added": "2026-08-08T00:00:00.000Z",
    "contributors": [
      "TheAnalogMaker"
    ],
    "sections": {
      "V3A": "unused — the D-FE layout page wires V3 pins 6, 7 and 8 only; pins 1, 2 and 3 are bare, and the schematic draws only V3B, the mixer/driver stage"
    }
  },
  "parts": {
    "notes": "The drawing shows both instrument jacks (1 and 2) of each channel with their normalling contacts; this sheet draws them as the two input labels, with the 1 MΩ leak at jack 1's tip, jack side of its 68 kΩ stopper, where D-FE puts it. The schematic draws ONE bias-supply filter capacitor, with polarity marks and no printed value; the layout page letters that one can 50 µF · 50 V. The output transformer's centre tap takes the HT on the reservoir side of the filter choke; the screens, the first 20 µF can and the 1 kΩ dropper hang on the choke's output. The 6L6GC pair is simulated on this corpus's own clean-room 6L6GC model.",
    "items": [
      {
        "ref": "R1b",
        "part": "Carbon comp resistor",
        "value": "68 kΩ · ½ W",
        "role": "Bass input grid stopper (jack 1)"
      },
      {
        "ref": "R2b",
        "part": "Carbon comp resistor",
        "value": "68 kΩ · ½ W",
        "role": "Bass input grid stopper (jack 2)"
      },
      {
        "ref": "RGB1",
        "part": "Carbon comp resistor",
        "value": "1 MΩ · ½ W",
        "role": "Bass input leak, jack 1's tip to ground (jack side of R1b); the grid's DC return through R1b"
      },
      {
        "ref": "RLB1",
        "part": "Carbon comp resistor",
        "value": "100 kΩ · ½ W",
        "role": "V1a plate load"
      },
      {
        "ref": "CLB1",
        "part": "Film capacitor",
        "value": "0.01 µF · 400 V",
        "role": "Treble-cut shunt across the V1a plate load"
      },
      {
        "ref": "RKB1",
        "part": "Carbon comp resistor",
        "value": "1.5 kΩ · ½ W",
        "role": "V1a cathode bias"
      },
      {
        "ref": "CKB1",
        "part": "Electrolytic capacitor",
        "value": "25 µF · 25 V",
        "role": "V1a cathode bypass"
      },
      {
        "ref": "CTB",
        "part": "Mica capacitor",
        "value": "330 pF",
        "role": "Bass-channel treble cap"
      },
      {
        "ref": "VRTB",
        "part": "Audio-taper potentiometer",
        "value": "250 kΩ-A",
        "role": "Bass channel Treble"
      },
      {
        "ref": "RSB",
        "part": "Carbon comp resistor",
        "value": "100 kΩ · ½ W",
        "role": "Bass-channel tone-stack slope resistor"
      },
      {
        "ref": "CBB",
        "part": "Coupling capacitor",
        "value": "0.1 µF",
        "role": "Bass-channel tone-stack bass cap, slope node to the treble-lug/bass node"
      },
      {
        "ref": "VRBB",
        "part": "Audio-taper potentiometer",
        "value": "250 kΩ-A",
        "role": "Bass channel Bass"
      },
      {
        "ref": "CBB2",
        "part": "Coupling capacitor",
        "value": "0.1 µF",
        "role": "Bass-channel tone-stack middle-leg cap, slope node to the bass-pot foot"
      },
      {
        "ref": "RSLB",
        "part": "Carbon comp resistor",
        "value": "8.2 kΩ · ½ W",
        "role": "Bass-channel tone-stack bleed resistor"
      },
      {
        "ref": "CDEEP",
        "part": "Coupling capacitor",
        "value": "0.1 µF",
        "role": "DEEP cap, tone-stack ladder foot to the switch"
      },
      {
        "ref": "SWDEEP",
        "part": "Switch",
        "value": "SPST",
        "role": "DEEP — grounds the extra bass cap"
      },
      {
        "ref": "VRVB",
        "part": "Audio-taper potentiometer",
        "value": "1 MΩ-A",
        "role": "Bass channel Volume"
      },
      {
        "ref": "RLB2",
        "part": "Carbon comp resistor",
        "value": "100 kΩ · ½ W",
        "role": "V1b plate load (drawn on the +320 V rail — see the circuit story)"
      },
      {
        "ref": "RKB2",
        "part": "Carbon comp resistor",
        "value": "1.5 kΩ · ½ W",
        "role": "V1b cathode bias"
      },
      {
        "ref": "CKB2",
        "part": "Electrolytic capacitor",
        "value": "25 µF · 25 V",
        "role": "V1b cathode bypass"
      },
      {
        "ref": "RMXB",
        "part": "Carbon comp resistor",
        "value": "220 kΩ · ½ W",
        "role": "Bass channel mixing resistor"
      },
      {
        "ref": "R1n",
        "part": "Carbon comp resistor",
        "value": "68 kΩ · ½ W",
        "role": "Normal input grid stopper (jack 1)"
      },
      {
        "ref": "R2n",
        "part": "Carbon comp resistor",
        "value": "68 kΩ · ½ W",
        "role": "Normal input grid stopper (jack 2)"
      },
      {
        "ref": "RGN1",
        "part": "Carbon comp resistor",
        "value": "1 MΩ · ½ W",
        "role": "Normal input leak, jack 1's tip to ground (jack side of R1n); the grid's DC return through R1n"
      },
      {
        "ref": "RLN1",
        "part": "Carbon comp resistor",
        "value": "100 kΩ · ½ W",
        "role": "V2a plate load"
      },
      {
        "ref": "RKN1",
        "part": "Carbon comp resistor",
        "value": "1.5 kΩ · ½ W",
        "role": "V2a cathode bias"
      },
      {
        "ref": "CKN1",
        "part": "Electrolytic capacitor",
        "value": "25 µF · 25 V",
        "role": "V2a cathode bypass"
      },
      {
        "ref": "CTN",
        "part": "Mica capacitor",
        "value": "250 pF",
        "role": "Normal-channel treble cap"
      },
      {
        "ref": "VRTN",
        "part": "Audio-taper potentiometer",
        "value": "250 kΩ-A",
        "role": "Normal channel Treble"
      },
      {
        "ref": "RSN",
        "part": "Carbon comp resistor",
        "value": "100 kΩ · ½ W",
        "role": "Normal-channel tone-stack slope resistor"
      },
      {
        "ref": "CBN",
        "part": "Coupling capacitor",
        "value": "0.1 µF",
        "role": "Normal-channel tone-stack bass cap, slope node to the treble-lug/bass node"
      },
      {
        "ref": "VRBN",
        "part": "Audio-taper potentiometer",
        "value": "250 kΩ-A",
        "role": "Normal channel Bass"
      },
      {
        "ref": "CBN2",
        "part": "Coupling capacitor",
        "value": "0.047 µF",
        "role": "Normal-channel tone-stack middle-leg cap, slope node to the bleed resistor"
      },
      {
        "ref": "RSLN",
        "part": "Carbon comp resistor",
        "value": "6.8 kΩ · ½ W",
        "role": "Normal-channel tone-stack bleed resistor"
      },
      {
        "ref": "CBRN",
        "part": "Mica capacitor",
        "value": "120 pF",
        "role": "Normal-channel bright cap, volume top lug to wiper"
      },
      {
        "ref": "SWBRT",
        "part": "Switch",
        "value": "SPST",
        "role": "BRIGHT — switches the 120 pF across the volume control"
      },
      {
        "ref": "VRVN",
        "part": "Audio-taper potentiometer",
        "value": "1 MΩ-A",
        "role": "Normal channel Volume"
      },
      {
        "ref": "RLN2",
        "part": "Carbon comp resistor",
        "value": "100 kΩ · ½ W",
        "role": "V2b plate load"
      },
      {
        "ref": "RKN2",
        "part": "Carbon comp resistor",
        "value": "1.5 kΩ · ½ W",
        "role": "V2b cathode bias"
      },
      {
        "ref": "CKN2",
        "part": "Electrolytic capacitor",
        "value": "25 µF · 25 V",
        "role": "V2b cathode bypass"
      },
      {
        "ref": "RMXN",
        "part": "Carbon comp resistor",
        "value": "220 kΩ · ½ W",
        "role": "Normal channel mixing resistor"
      },
      {
        "ref": "RFBM",
        "part": "Carbon comp resistor",
        "value": "470 kΩ · ½ W",
        "role": "V3b plate back to the mixing node — the AB165 blend/feedback resistor"
      },
      {
        "ref": "CMIX",
        "part": "Film capacitor",
        "value": "0.01 µF · 400 V",
        "role": "Mixing node → V3b grid coupling"
      },
      {
        "ref": "RGM",
        "part": "Carbon comp resistor",
        "value": "470 kΩ · ½ W",
        "role": "V3b grid leak"
      },
      {
        "ref": "RLM",
        "part": "Carbon comp resistor",
        "value": "100 kΩ · ½ W",
        "role": "V3b plate load"
      },
      {
        "ref": "RKM",
        "part": "Carbon comp resistor",
        "value": "1.5 kΩ · ½ W",
        "role": "V3b cathode bias"
      },
      {
        "ref": "CKM",
        "part": "Electrolytic capacitor",
        "value": "25 µF · 25 V",
        "role": "V3b cathode bypass"
      },
      {
        "ref": "CPIA",
        "part": "Coupling capacitor",
        "value": "0.1 µF · 400 V",
        "role": "V3b plate → PI hot grid"
      },
      {
        "ref": "RLPA",
        "part": "Carbon comp resistor",
        "value": "100 kΩ · ½ W · 5%",
        "role": "PI plate load (hot side)"
      },
      {
        "ref": "RLPB",
        "part": "Carbon comp resistor",
        "value": "100 kΩ · ½ W · 5%",
        "role": "PI plate load (cold side)"
      },
      {
        "ref": "RGPA",
        "part": "Carbon comp resistor",
        "value": "1 MΩ · ½ W",
        "role": "PI grid leak (hot), returned to the tail junction"
      },
      {
        "ref": "RGPB",
        "part": "Carbon comp resistor",
        "value": "1 MΩ · ½ W",
        "role": "PI grid leak (cold), returned to the tail junction"
      },
      {
        "ref": "RTAIL",
        "part": "Carbon comp resistor",
        "value": "470 Ω · ½ W",
        "role": "PI cathode resistor"
      },
      {
        "ref": "RT2",
        "part": "Carbon comp resistor",
        "value": "22 kΩ · ½ W",
        "role": "PI tail (junction → ground)"
      },
      {
        "ref": "CPIB",
        "part": "Film capacitor",
        "value": "0.1 µF · 200 V",
        "role": "PI cold-grid AC ground"
      },
      {
        "ref": "RBSA",
        "part": "Carbon comp resistor",
        "value": "220 kΩ · ½ W",
        "role": "Local feedback, V5 plate → PI hot plate"
      },
      {
        "ref": "RBSB",
        "part": "Carbon comp resistor",
        "value": "220 kΩ · ½ W",
        "role": "Local feedback, V6 plate → PI cold plate"
      },
      {
        "ref": "C1",
        "part": "Film capacitor",
        "value": "0.022 µF · 400 V",
        "role": "PI hot plate → V5 grid"
      },
      {
        "ref": "C2",
        "part": "Film capacitor",
        "value": "0.022 µF · 400 V",
        "role": "PI cold plate → V6 grid"
      },
      {
        "ref": "RGL1",
        "part": "Carbon comp resistor",
        "value": "220 kΩ · ½ W · 5%",
        "role": "V5 grid leak, from the BIAS BALANCE wiper (the sheet's −45 V)"
      },
      {
        "ref": "RGL2",
        "part": "Carbon comp resistor",
        "value": "220 kΩ · ½ W · 5%",
        "role": "V6 grid leak, from the junction of the two 10 kΩ bias legs"
      },
      {
        "ref": "RGS1",
        "part": "Carbon comp resistor",
        "value": "1.5 kΩ · ½ W",
        "role": "V5 grid stopper"
      },
      {
        "ref": "RGS2",
        "part": "Carbon comp resistor",
        "value": "1.5 kΩ · ½ W",
        "role": "V6 grid stopper"
      },
      {
        "ref": "RS1",
        "part": "Wirewound resistor",
        "value": "470 Ω · 1 W",
        "role": "V5 screen resistor"
      },
      {
        "ref": "RS2",
        "part": "Wirewound resistor",
        "value": "470 Ω · 1 W",
        "role": "V6 screen resistor"
      },
      {
        "ref": "TR3",
        "part": "Output transformer",
        "value": "Fender 125A13A",
        "role": "Push-pull 6L6GC output; centre tap on the reservoir side of the choke"
      },
      {
        "ref": "RNFB",
        "part": "Carbon comp resistor",
        "value": "47 kΩ · ½ W",
        "role": "Negative feedback, speaker line → PI hot grid (DC-blocked)"
      },
      {
        "ref": "CNFB",
        "part": "Coupling capacitor",
        "value": "0.1 µF · 400 V",
        "role": "Negative-feedback series capacitor"
      },
      {
        "ref": "TR1",
        "part": "Power transformer",
        "value": "Fender 125P7D · 320-0-320 V",
        "role": "HT + heaters (export model 125P7DX)"
      },
      {
        "ref": "TR2",
        "part": "Filter choke",
        "value": "Fender 125C1A",
        "role": "Reservoir → screen rail"
      },
      {
        "ref": "D1",
        "part": "Rectifier diode",
        "value": "silicon (×3 in series)",
        "role": "HT rectifier, upper leg"
      },
      {
        "ref": "D2",
        "part": "Rectifier diode",
        "value": "silicon (×3 in series)",
        "role": "HT rectifier, lower leg"
      },
      {
        "ref": "SWSTBY",
        "part": "Switch",
        "value": "SPST",
        "role": "Standby — breaks the HT rail ahead of the choke"
      },
      {
        "ref": "C10",
        "part": "Electrolytic capacitor",
        "value": "70 µF · 350 V",
        "role": "Reservoir filter, upper half of the series pair"
      },
      {
        "ref": "C11",
        "part": "Electrolytic capacitor",
        "value": "70 µF · 350 V",
        "role": "Reservoir filter, lower half of the series pair"
      },
      {
        "ref": "RBAL1",
        "part": "Carbon comp resistor",
        "value": "220 kΩ · 1 W",
        "role": "Reservoir balancing resistor (upper)"
      },
      {
        "ref": "RBAL2",
        "part": "Carbon comp resistor",
        "value": "220 kΩ · 1 W",
        "role": "Reservoir balancing resistor (lower)"
      },
      {
        "ref": "C12",
        "part": "Electrolytic capacitor",
        "value": "20 µF · 525 V",
        "role": "Filter, screen node (+425, after the choke)"
      },
      {
        "ref": "RD1",
        "part": "Carbon comp resistor",
        "value": "1 kΩ · 1 W",
        "role": "Rail dropper, screen node → phase-inverter node"
      },
      {
        "ref": "C13",
        "part": "Electrolytic capacitor",
        "value": "20 µF · 525 V",
        "role": "Filter, phase-inverter node (+415)"
      },
      {
        "ref": "RD2",
        "part": "Carbon comp resistor",
        "value": "4.7 kΩ · 1 W",
        "role": "Rail dropper, +415 → second-stage node"
      },
      {
        "ref": "C14",
        "part": "Electrolytic capacitor",
        "value": "20 µF · 525 V",
        "role": "Filter, second-stage node (+390)"
      },
      {
        "ref": "RD3",
        "part": "Carbon comp resistor",
        "value": "27 kΩ · 1 W",
        "role": "Rail dropper, +390 → input-stage node"
      },
      {
        "ref": "C15",
        "part": "Electrolytic capacitor",
        "value": "8 µF · 450 V",
        "role": "Filter, input-stage node (+320)"
      },
      {
        "ref": "RBIAS",
        "part": "Wirewound resistor",
        "value": "470 Ω · 1 W",
        "role": "Bias-supply series resistor off the HT winding"
      },
      {
        "ref": "DBIAS",
        "part": "Rectifier (bias)",
        "value": "silicon diode",
        "role": "Bias-supply rectifier"
      },
      {
        "ref": "CB1",
        "part": "Electrolytic capacitor",
        "value": "50 µF · 50 V",
        "role": "Bias-supply filter, the diode's negative node to ground (+ to ground). The D-FE layout page letters it '50 | 50' with + and − marks, the one electrolytic on its bias board (layout 2148x1578, crop 170,400,920,680); the schematic draws the one capacitor and prints no value (crop 4500,2450,5700,3300)"
      },
      {
        "ref": "RBB1",
        "part": "Carbon comp resistor",
        "value": "10 kΩ · ½ W",
        "role": "Bias bridge leg, the balance pot's 15 kΩ end → V6's grid-leak return"
      },
      {
        "ref": "RBB2",
        "part": "Carbon comp resistor",
        "value": "10 kΩ · ½ W",
        "role": "Bias bridge leg, the balance pot's diode end → V6's grid-leak return"
      },
      {
        "ref": "RBB3",
        "part": "Carbon comp resistor",
        "value": "15 kΩ · ½ W",
        "role": "Bias divider foot, the balance pot's far end to ground"
      },
      {
        "ref": "VRBAL",
        "part": "Linear potentiometer",
        "value": "10 kΩ-L",
        "role": "BIAS BALANCE — the sheet's 'hum balance' control; across the bias node and the 15 kΩ foot, its wiper is V5's −45 V return"
      },
      {
        "ref": "SWAC",
        "part": "Switch",
        "value": "SPST",
        "role": "AC switch"
      },
      {
        "ref": "F1",
        "part": "Fuse",
        "value": "2 A slo-blo",
        "role": "Mains fuse"
      },
      {
        "ref": "SWGND",
        "part": "Switch",
        "value": "SPDT",
        "role": "Ground switch (period; not in modern builds)"
      },
      {
        "ref": "CDEATH",
        "part": "Ceramic capacitor",
        "value": "0.047 µF · 600 V",
        "role": "Ground-switch cap (period; not in modern builds)"
      },
      {
        "ref": "V1",
        "part": "Preamp tube",
        "value": "12AX7 (7025)",
        "role": "Bass channel input + second stage (V1a/V1b)"
      },
      {
        "ref": "V2",
        "part": "Preamp tube",
        "value": "12AX7 (7025)",
        "role": "Normal channel input + second stage (V2a/V2b)"
      },
      {
        "ref": "V3",
        "part": "Preamp tube",
        "value": "12AX7 (7025)",
        "role": "Mixer/driver stage (V3b)"
      },
      {
        "ref": "V4",
        "part": "Preamp/driver tube",
        "value": "12AT7",
        "role": "Long-tailed-pair phase inverter"
      },
      {
        "ref": "V5",
        "part": "Power tube",
        "value": "6L6GC",
        "role": "Push-pull output (hot side)"
      },
      {
        "ref": "V6",
        "part": "Power tube",
        "value": "6L6GC",
        "role": "Push-pull output (cold side)"
      }
    ]
  },
  "publishedVoltages": {
    "source": "Fender Bassman-Amp AB165 drawing (D-FE), printed voltages: +425 (6L6GC plates pin 3 and screens pin 4, both bottles), +415 (phase-inverter supply), +390 (second-stage supply), +320 (input-stage supply), -45 (bias line at the 10 kOhm-L balance control); bass channel +220/+1.6 (V1a plate/cathode) and +260/+1.8 (V1b); normal channel +280/+1.9 (V2a) and +260/+1.9 (V2b); mixer-driver +250/+2.0 (V3b); phase inverter +225 and +220 plates over +102 joined cathodes and +100 tail junction",
    "nodes": {
      "BPI": {
        "chart": 415,
        "tol_pct": 5,
        "note": "phase-inverter supply, +425 through the 1 kOhm-1W dropper"
      },
      "BD": {
        "chart": 390,
        "tol_pct": 5,
        "note": "second-stage supply, +415 through the 4.7 kOhm-1W dropper"
      },
      "BC": {
        "chart": 320,
        "tol_pct": 8,
        "note": "input-stage supply, +390 through the 27 kOhm-1W dropper — the end of the ladder and the node most sensitive to preamp current"
      },
      "SO1": {
        "chart": 425,
        "tol_pct": 8,
        "note": "V5 (6L6GC) screen after its 470 Ohm-1W stopper, off the +425 rail"
      },
      "SO2": {
        "chart": 425,
        "tol_pct": 8,
        "note": "V6 (6L6GC) screen after its 470 Ohm-1W stopper"
      },
      "GO1": {
        "chart": -45,
        "tol_pct": 8,
        "note": "V5 grid leak node, fixed bias via 220k-5% from the -45 V line"
      },
      "GO2": {
        "chart": -45,
        "tol_pct": 8,
        "note": "V6 grid leak node"
      },
      "PPIA": {
        "chart": 225,
        "tol_pct": 20,
        "note": "PI plate, pin 1 — 100k 5% from +415 with the 220k local feedback resistor from the output plate rail"
      },
      "PPIB": {
        "chart": 220,
        "tol_pct": 20,
        "note": "PI plate, pin 6 — the drawing draws both plate loads at 100k 5%, so the 5 V split it prints between the two plates is meter scatter, not circuit asymmetry"
      },
      "KPI": {
        "chart": 102,
        "tol_pct": 20,
        "note": "PI joined cathodes (pins 3 and 8), above the 470 Ohm"
      },
      "JPI": {
        "chart": 100,
        "tol_pct": 20,
        "note": "PI tail junction (470 Ohm / 22k), both 1M grid leaks return here"
      },
      "PM": {
        "chart": 250,
        "tol_pct": 20,
        "note": "V3b plate, 100k from +390"
      },
      "KM": {
        "chart": 2,
        "tol_pct": 20,
        "note": "V3b cathode over 1.5k"
      },
      "PB1": {
        "chart": 220,
        "tol_pct": 20,
        "note": "V1a plate, 100k from +320 with the 0.01 uF treble-cut shunt across it"
      },
      "KB1": {
        "chart": 1.6,
        "tol_pct": 20,
        "note": "V1a cathode over 1.5k"
      },
      "PB2": {
        "chart": 260,
        "disputed": true,
        "dispute_note": "The sheet draws V1b's 100 kOhm plate load on the +320 V rail (its right-hand corner turns back along that rail; the +390 V line below it is a separate wire the branch to the normal channel leaves from), and prints +1.8 V at V1b's cathode over 1.5 kOhm. Those two printed numbers give 1.2 mA, which drops 120 V in the printed 100 kOhm and leaves +200 V at the plate, not the printed +260 V; run backwards, +260 V through the same 100 kOhm is 0.6 mA, which over 1.5 kOhm is +0.9 V at the cathode, not the printed +1.8 V. The printed +260 V is the value this stage would carry if it hung on +390 V like the normal channel's identical second stage, which the chart also prints at +260 V. Reported, not gated.",
        "note": "V1b plate — printed +260 V; see dispute_note"
      },
      "KB2": {
        "chart": 1.8,
        "tol_pct": 20,
        "note": "V1b cathode over 1.5k"
      },
      "PN1": {
        "chart": 280,
        "disputed": true,
        "dispute_note": "V2a is V1a's twin — 100 kOhm plate load, 1.5 kOhm cathode, both drawn on the same +320 V rail — yet the chart prints +220 V/+1.6 V on the bass channel and +280 V/+1.9 V on the normal one. The pair moves the wrong way against itself: the higher printed cathode voltage means MORE plate current (1.9 V over 1.5 kOhm = 1.27 mA against 1.6 V = 1.07 mA), and more current through the same 100 kOhm must give a LOWER plate, +193 V rather than the +220 V of its twin — never the +280 V printed. Reported, not gated; the cathode pin beside it (KN1) is gated normally.",
        "note": "V2a plate — printed +280 V; see dispute_note"
      },
      "KN1": {
        "chart": 1.9,
        "tol_pct": 20,
        "note": "V2a cathode over 1.5k"
      },
      "PN2": {
        "chart": 260,
        "tol_pct": 20,
        "note": "V2b plate, 100k from +390"
      },
      "KN2": {
        "chart": 1.9,
        "tol_pct": 20,
        "note": "V2b cathode over 1.5k"
      }
    }
  },
  "operatingPoint": [
    {
      "node": "BPI",
      "chart": 415,
      "sim": 416.149,
      "disputed": false,
      "dev_pct": 0.27686746987951827,
      "tol_pct": 5,
      "gated": true,
      "within": true,
      "note": "phase-inverter supply, +425 through the 1 kOhm-1W dropper",
      "dispute_note": ""
    },
    {
      "node": "BD",
      "chart": 390,
      "sim": 388.919,
      "disputed": false,
      "dev_pct": 0.2771794871794916,
      "tol_pct": 5,
      "gated": true,
      "within": true,
      "note": "second-stage supply, +415 through the 4.7 kOhm-1W dropper",
      "dispute_note": ""
    },
    {
      "node": "BC",
      "chart": 320,
      "sim": 305.879,
      "disputed": false,
      "dev_pct": 4.412812499999994,
      "tol_pct": 8,
      "gated": true,
      "within": true,
      "note": "input-stage supply, +390 through the 27 kOhm-1W dropper — the end of the ladder and the node most sensitive to preamp current",
      "dispute_note": ""
    },
    {
      "node": "SO1",
      "chart": 425,
      "sim": 424.253,
      "disputed": false,
      "dev_pct": 0.17576470588235626,
      "tol_pct": 8,
      "gated": true,
      "within": true,
      "note": "V5 (6L6GC) screen after its 470 Ohm-1W stopper, off the +425 rail",
      "dispute_note": ""
    },
    {
      "node": "SO2",
      "chart": 425,
      "sim": 424.253,
      "disputed": false,
      "dev_pct": 0.17576470588235626,
      "tol_pct": 8,
      "gated": true,
      "within": true,
      "note": "V6 (6L6GC) screen after its 470 Ohm-1W stopper",
      "dispute_note": ""
    },
    {
      "node": "GO1",
      "chart": -45,
      "sim": -45,
      "disputed": false,
      "dev_pct": 0,
      "tol_pct": 8,
      "gated": true,
      "within": true,
      "note": "V5 grid leak node, fixed bias via 220k-5% from the -45 V line",
      "dispute_note": ""
    },
    {
      "node": "GO2",
      "chart": -45,
      "sim": -45,
      "disputed": false,
      "dev_pct": 0,
      "tol_pct": 8,
      "gated": true,
      "within": true,
      "note": "V6 grid leak node",
      "dispute_note": ""
    },
    {
      "node": "PPIA",
      "chart": 225,
      "sim": 263.29,
      "disputed": false,
      "dev_pct": 17.017777777777788,
      "tol_pct": 20,
      "gated": true,
      "within": true,
      "note": "PI plate, pin 1 — 100k 5% from +415 with the 220k local feedback resistor from the output plate rail",
      "dispute_note": ""
    },
    {
      "node": "PPIB",
      "chart": 220,
      "sim": 263.29,
      "disputed": false,
      "dev_pct": 19.677272727272737,
      "tol_pct": 20,
      "gated": true,
      "within": true,
      "note": "PI plate, pin 6 — the drawing draws both plate loads at 100k 5%, so the 5 V split it prints between the two plates is meter scatter, not circuit asymmetry",
      "dispute_note": ""
    },
    {
      "node": "KPI",
      "chart": 102,
      "sim": 101.728,
      "disputed": false,
      "dev_pct": 0.2666666666666721,
      "tol_pct": 20,
      "gated": true,
      "within": true,
      "note": "PI joined cathodes (pins 3 and 8), above the 470 Ohm",
      "dispute_note": ""
    },
    {
      "node": "JPI",
      "chart": 100,
      "sim": 99.6,
      "disputed": false,
      "dev_pct": 0.40000000000000563,
      "tol_pct": 20,
      "gated": true,
      "within": true,
      "note": "PI tail junction (470 Ohm / 22k), both 1M grid leaks return here",
      "dispute_note": ""
    },
    {
      "node": "PM",
      "chart": 250,
      "sim": 254.226,
      "disputed": false,
      "dev_pct": 1.6903999999999995,
      "tol_pct": 20,
      "gated": true,
      "within": true,
      "note": "V3b plate, 100k from +390",
      "dispute_note": ""
    },
    {
      "node": "KM",
      "chart": 2,
      "sim": 1.958,
      "disputed": false,
      "dev_pct": 2.100000000000002,
      "tol_pct": 20,
      "gated": true,
      "within": true,
      "note": "V3b cathode over 1.5k",
      "dispute_note": ""
    },
    {
      "node": "PB1",
      "chart": 220,
      "sim": 200.666,
      "disputed": false,
      "dev_pct": 8.78818181818182,
      "tol_pct": 20,
      "gated": true,
      "within": true,
      "note": "V1a plate, 100k from +320 with the 0.01 uF treble-cut shunt across it",
      "dispute_note": ""
    },
    {
      "node": "KB1",
      "chart": 1.6,
      "sim": 1.578,
      "disputed": false,
      "dev_pct": 1.3750000000000013,
      "tol_pct": 20,
      "gated": true,
      "within": true,
      "note": "V1a cathode over 1.5k",
      "dispute_note": ""
    },
    {
      "node": "PB2",
      "chart": 260,
      "sim": 208.747,
      "disputed": true,
      "dev_pct": 19.712692307692304,
      "tol_pct": 5,
      "gated": false,
      "within": null,
      "note": "V1b plate — printed +260 V; see dispute_note",
      "dispute_note": "The sheet draws V1b's 100 kOhm plate load on the +320 V rail (its right-hand corner turns back along that rail; the +390 V line below it is a separate wire the branch to the normal channel leaves from), and prints +1.8 V at V1b's cathode over 1.5 kOhm. Those two printed numbers give 1.2 mA, which drops 120 V in the printed 100 kOhm and leaves +200 V at the plate, not the printed +260 V; run backwards, +260 V through the same 100 kOhm is 0.6 mA, which over 1.5 kOhm is +0.9 V at the cathode, not the printed +1.8 V. The printed +260 V is the value this stage would carry if it hung on +390 V like the normal channel's identical second stage, which the chart also prints at +260 V. Reported, not gated."
    },
    {
      "node": "KB2",
      "chart": 1.8,
      "sim": 1.635,
      "disputed": false,
      "dev_pct": 9.16666666666667,
      "tol_pct": 20,
      "gated": true,
      "within": true,
      "note": "V1b cathode over 1.5k",
      "dispute_note": ""
    },
    {
      "node": "PN1",
      "chart": 280,
      "sim": 200.666,
      "disputed": true,
      "dev_pct": 28.33357142857143,
      "tol_pct": 5,
      "gated": false,
      "within": null,
      "note": "V2a plate — printed +280 V; see dispute_note",
      "dispute_note": "V2a is V1a's twin — 100 kOhm plate load, 1.5 kOhm cathode, both drawn on the same +320 V rail — yet the chart prints +220 V/+1.6 V on the bass channel and +280 V/+1.9 V on the normal one. The pair moves the wrong way against itself: the higher printed cathode voltage means MORE plate current (1.9 V over 1.5 kOhm = 1.27 mA against 1.6 V = 1.07 mA), and more current through the same 100 kOhm must give a LOWER plate, +193 V rather than the +220 V of its twin — never the +280 V printed. Reported, not gated; the cathode pin beside it (KN1) is gated normally."
    },
    {
      "node": "KN1",
      "chart": 1.9,
      "sim": 1.578,
      "disputed": false,
      "dev_pct": 16.947368421052627,
      "tol_pct": 20,
      "gated": true,
      "within": true,
      "note": "V2a cathode over 1.5k",
      "dispute_note": ""
    },
    {
      "node": "PN2",
      "chart": 260,
      "sim": 251.802,
      "disputed": false,
      "dev_pct": 3.153076923076926,
      "tol_pct": 20,
      "gated": true,
      "within": true,
      "note": "V2b plate, 100k from +390",
      "dispute_note": ""
    },
    {
      "node": "KN2",
      "chart": 1.9,
      "sim": 1.941,
      "disputed": false,
      "dev_pct": 2.1578947368421133,
      "tol_pct": 20,
      "gated": true,
      "within": true,
      "note": "V2b cathode over 1.5k",
      "dispute_note": ""
    }
  ],
  "checks": [
    {
      "id": "dc",
      "title": "DC operating point",
      "status": "Verified",
      "summary": "19 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.",
        "28 sheet-only parts are explicitly excluded: C10, C11, C12, C13, C14, C15, CB1, CBRN, CDEATH, D1, D2, DBIAS, F1, R1b, R1n, R2b, R2n, RBAL1, RBAL2, RBB1, RBB2, RBB3, RBIAS, RGB1, RGN1, RSLB, RSLN, VRBAL. 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": "5 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": "ab165-bias-filter-2026-10-03",
      "date": "2026-10-03",
      "amps": [
        "ab165"
      ],
      "title": "AB165 bias filter capacitor value from the factory layout",
      "description": "The bias supply's single filter capacitor is now listed as 50 µF at 50 V, as the factory layout drawing letters it; the schematic gives no value. The layout drawing is now cited as a source, and it agrees with the schematic on the one capacitor, the bias-balance network and the bass channel's 330 pF treble capacitor. No operating point changes.",
      "commit": "45797e5ff9dba81ab4bdc52d6cc27fd0ef377c2c",
      "url": "https://github.com/TheAnalogMaker/circuit-codex/commit/45797e5ff9dba81ab4bdc52d6cc27fd0ef377c2c"
    },
    {
      "id": "ab165-tone-ot-bias-2026-10-03",
      "date": "2026-10-03",
      "amps": [
        "ab165"
      ],
      "title": "AB165 input leaks, bass treble capacitor, output-transformer feed and bias network",
      "description": "The bass channel's treble capacitor is 330 pF, as the factory drawing letters it; it had been listed as 390 pF. The output transformer's centre tap now takes its supply ahead of the choke, on both the schematic and the board. The bias network is drawn as the factory bridge, with its single filter capacitor, and the input leaks hang from input 1's tip. No operating point changes.",
      "commit": "af8686c93885be5cb356a0071fb08fb848d5f8e9",
      "url": "https://github.com/TheAnalogMaker/circuit-codex/commit/af8686c93885be5cb356a0071fb08fb848d5f8e9"
    }
  ],
  "sourceDirectory": "https://github.com/TheAnalogMaker/circuit-codex/tree/ebddc3fd2cf887dca010bbe60487d7391ea6c052/amps/ab165"
}