{
  "format": "circuit-codex-reference",
  "version": 1,
  "id": "5f10",
  "url": "https://circuitcodex.com/amps/5f10/",
  "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": "5f10",
    "name_style": "Tweed Harvard-style",
    "family": "tweed",
    "era": {
      "start": 1958,
      "end": 1961
    },
    "wattage": 10,
    "tubes": [
      "6AT6",
      "12AX7",
      "6V6GT",
      "6V6GT",
      "5Y3GT"
    ],
    "topology": {
      "rectifier": {
        "kind": "tube",
        "type": "5Y3GT"
      },
      "bias": "fixed",
      "phase_inverter": "cathodyne",
      "tone_stack": "single-knob"
    },
    "lineage": {
      "derived_from": [],
      "influenced": []
    },
    "conventions": {
      "designators": "functional"
    },
    "sources": [
      {
        "desc": "Fender 'Harvard' Model 5F10 drawing (F-EF), schematic + layout: every component value AND the printed voltage chart read directly from the published sheet (+305/+302/+250 rails, -27 V fixed bias, tube pins; cathodyne PI = 56k plate + 1.5k/56k cathode with the 1M leak to the junction; 470 R screen dropper + 22k; 56k negative feedback to the driver cathode). Not reproduced here; archived at EL34World",
        "url": "https://el34world.com/charts/Schematics/files/Fender/Fender_harvard_5f10_schem.pdf"
      },
      {
        "desc": "RCA 6AT6 datasheet (twin-diode / high-mu triode, Sept 1955) — triode Class-A anchor for the clean-room CC0 tube model (Va=250 V, Vg=-3 V, mu=70, rp=58k, gm=1200 umho, Ia=1 mA); only the triode section is used",
        "url": "https://frank.pocnet.net/sheets/049/6/6AT6.pdf"
      }
    ],
    "verification": {
      "status": "verified",
      "date": "2026-07-18T00:00:00.000Z",
      "max_deviation_pct": 15.2
    },
    "contributors": [
      "TheAnalogMaker"
    ]
  },
  "parts": {
    "notes": "The chassis has three input jacks (1/2/3), each with its own 68 kΩ stopper; the 6AT6 grid returns to ground through the switched jacks. Only the 6AT6 triode section is used (its twin diodes are unwired). Parts drawn only as annotations (power transformer, AC-line caps, fuse, switch, pilot lamp) are listed without designators.",
    "items": [
      {
        "ref": "JI1",
        "part": "Jack socket, switched",
        "value": "1/4 in",
        "role": "Input 1 — unplugged, its normalling contact grounds its own tip: the 6AT6 grid's DC return through R1s (no grid leak)"
      },
      {
        "ref": "JI2",
        "part": "Jack socket, switched",
        "value": "1/4 in",
        "role": "Input 2 — unplugged, its normalling contact ties its tip to jack 1's tip"
      },
      {
        "ref": "JI3",
        "part": "Jack socket, switched",
        "value": "1/4 in",
        "role": "Input 3 — unplugged, its normalling contact ties its tip to jack 2's tip"
      },
      {
        "ref": "R1s",
        "part": "Carbon comp resistor",
        "value": "68 kΩ · ½ W",
        "role": "Input 1 grid stopper (grid returns to ground through this jack)"
      },
      {
        "ref": "R2s",
        "part": "Carbon comp resistor",
        "value": "68 kΩ · ½ W",
        "role": "Input 2 grid stopper"
      },
      {
        "ref": "R3s",
        "part": "Carbon comp resistor",
        "value": "68 kΩ · ½ W",
        "role": "Input 3 grid stopper"
      },
      {
        "ref": "RL1",
        "part": "Carbon comp resistor",
        "value": "100 kΩ · ½ W",
        "role": "6AT6 plate load"
      },
      {
        "ref": "RK1",
        "part": "Carbon comp resistor",
        "value": "1.5 kΩ · ½ W",
        "role": "6AT6 cathode bias"
      },
      {
        "ref": "C1",
        "part": "Electrolytic capacitor",
        "value": "25 µF · 25 V",
        "role": "6AT6 cathode bypass"
      },
      {
        "ref": "C2",
        "part": "Coupling capacitor",
        "value": "0.02 µF · 400 V",
        "role": "6AT6 plate → volume"
      },
      {
        "ref": "VR1",
        "part": "Linear potentiometer",
        "value": "1 MΩ",
        "role": "Volume"
      },
      {
        "ref": "C3",
        "part": "Mica capacitor",
        "value": "500 pF",
        "role": "Tone network: from the tone pot's other end lug to the volume wiper (the treble path)"
      },
      {
        "ref": "VR2",
        "part": "Audio-taper potentiometer",
        "value": "1 MΩ",
        "role": "Tone — wiper on the volume's input lug; its two ends carry C4 and C3, so it blends between a cut and a treble path"
      },
      {
        "ref": "C4",
        "part": "Film capacitor",
        "value": "0.005 µF",
        "role": "Tone network: from one end lug of the tone pot to ground (the cut path)"
      },
      {
        "ref": "RL2",
        "part": "Carbon comp resistor",
        "value": "100 kΩ · ½ W",
        "role": "12AX7 driver plate load"
      },
      {
        "ref": "RK2",
        "part": "Carbon comp resistor",
        "value": "1.5 kΩ · ½ W",
        "role": "12AX7 driver cathode bias (unbypassed)"
      },
      {
        "ref": "RNFB",
        "part": "Carbon comp resistor",
        "value": "56 kΩ · ½ W",
        "role": "Negative feedback, speaker → driver cathode"
      },
      {
        "ref": "C5",
        "part": "Coupling capacitor",
        "value": "0.02 µF · 400 V",
        "role": "Driver plate → phase-inverter grid"
      },
      {
        "ref": "RGPI",
        "part": "Carbon comp resistor",
        "value": "1 MΩ · ½ W",
        "role": "Cathodyne grid leak, returned to the cathode junction"
      },
      {
        "ref": "RL3",
        "part": "Carbon comp resistor",
        "value": "56 kΩ · ½ W",
        "role": "Cathodyne plate load"
      },
      {
        "ref": "RKA",
        "part": "Carbon comp resistor",
        "value": "1.5 kΩ · ½ W",
        "role": "Cathodyne bias (cathode → junction)"
      },
      {
        "ref": "RKB",
        "part": "Carbon comp resistor",
        "value": "56 kΩ · ½ W",
        "role": "Cathodyne cathode load (junction → ground)"
      },
      {
        "ref": "C6",
        "part": "Coupling capacitor",
        "value": "0.1 µF · 400 V",
        "role": "PI plate → upper 6V6 grid"
      },
      {
        "ref": "C7",
        "part": "Coupling capacitor",
        "value": "0.1 µF · 200 V",
        "role": "PI cathode → lower 6V6 grid"
      },
      {
        "ref": "Rs1",
        "part": "Carbon comp resistor",
        "value": "1.5 kΩ · ½ W",
        "role": "Upper 6V6 grid stopper"
      },
      {
        "ref": "Rs2",
        "part": "Carbon comp resistor",
        "value": "1.5 kΩ · ½ W",
        "role": "Lower 6V6 grid stopper"
      },
      {
        "ref": "RG1",
        "part": "Carbon comp resistor",
        "value": "220 kΩ · ½ W",
        "role": "Upper 6V6 grid leak, from the −27 V bias line"
      },
      {
        "ref": "RG2",
        "part": "Carbon comp resistor",
        "value": "220 kΩ · ½ W",
        "role": "Lower 6V6 grid leak, from the −27 V bias line"
      },
      {
        "ref": "RD1",
        "part": "Carbon comp resistor",
        "value": "470 Ω · 1 W",
        "role": "6V6 screen dropper B+1 → B+2"
      },
      {
        "ref": "RD2",
        "part": "Power resistor",
        "value": "22 kΩ",
        "role": "Rail dropper B+2 → B+3"
      },
      {
        "ref": "C8",
        "part": "Electrolytic capacitor",
        "value": "16 µF · 450 V",
        "role": "Filter, B+1"
      },
      {
        "ref": "C9",
        "part": "Electrolytic capacitor",
        "value": "16 µF · 450 V",
        "role": "Filter, B+2"
      },
      {
        "ref": "C10",
        "part": "Electrolytic capacitor",
        "value": "16 µF · 450 V",
        "role": "Filter, B+3"
      },
      {
        "ref": "D1",
        "part": "Rectifier (bias)",
        "value": "selenium (silicon diode in modern builds)",
        "role": "Bias-supply rectifier"
      },
      {
        "ref": "RB1",
        "part": "Carbon comp resistor",
        "value": "6.8 kΩ · ½ W",
        "role": "Bias supply series resistor"
      },
      {
        "ref": "RB2",
        "part": "Carbon comp resistor",
        "value": "56 kΩ · ½ W",
        "role": "Bias supply bleeder"
      },
      {
        "ref": "C11",
        "part": "Electrolytic capacitor",
        "value": "25 µF · 25 V",
        "role": "Bias supply filter, −27 V line to ground (one can; the layout page prints \"25MF. 25V.\")"
      },
      {
        "ref": "V1",
        "part": "Preamp tube",
        "value": "6AT6",
        "role": "First gain stage (triode section; twin diodes unused)"
      },
      {
        "ref": "V2",
        "part": "Preamp tube",
        "value": "12AX7",
        "role": "Driver + cathodyne phase inverter (V2A/V2B)"
      },
      {
        "ref": "V3",
        "part": "Power tube",
        "value": "6V6GT",
        "role": "Push-pull output (upper)"
      },
      {
        "ref": "V4",
        "part": "Power tube",
        "value": "6V6GT",
        "role": "Push-pull output (lower)"
      },
      {
        "ref": "V5",
        "part": "Rectifier tube",
        "value": "5Y3GT",
        "role": "Full-wave rectifier (V5A/V5B)"
      },
      {
        "ref": "T1",
        "part": "Output transformer",
        "value": "Push-pull (impedance ratio not printed on the drawing)",
        "role": "Push-pull output into the speaker"
      },
      {
        "ref": "T2",
        "part": "Power transformer",
        "value": "HT (center-tapped, bias tap) · 6.3 V · 5 V",
        "role": "HT winding with a centre tap and a bias tap between one end and the centre tap (the white lead) + heaters + rectifier filament (no part number on the drawing)"
      },
      {
        "ref": "—",
        "part": "Film capacitor",
        "value": "0.05 µF · 600 V",
        "role": "AC-line filter cap, fuse to ground (one on both pages; annotation only)"
      },
      {
        "ref": "—",
        "part": "Fuse",
        "value": "¾ A",
        "role": "AC mains fuse (annotation only)"
      },
      {
        "ref": "—",
        "part": "Switch",
        "value": "SPST",
        "role": "AC power switch (annotation only)"
      },
      {
        "ref": "—",
        "part": "Pilot lamp",
        "value": "6.3 V (bulb type not printed)",
        "role": "Pilot light (annotation only)"
      }
    ]
  },
  "publishedVoltages": {
    "source": "Fender Harvard 5F10 (F-EF) drawing, printed voltages: rails +305 (plates)/+302 (screens)/+250 (preamp); 6AT6 plate +160, cathode +1.3; 12AX7 driver plate +170, cathode +1.5; cathodyne PI plate +207, cathode +44.3, junction +43; 6V6 fixed bias -27 (printed on both the schematic and the layout page)",
    "nodes": {
      "BP2": {
        "chart": 302,
        "tol_pct": 8,
        "note": "6V6 screen node, after the 470 ohm"
      },
      "BP3": {
        "chart": 250,
        "tol_pct": 8,
        "note": "preamp/PI supply node, after the 22 k dropper"
      },
      "PAT": {
        "chart": 160,
        "tol_pct": 20,
        "note": "6AT6 plate, printed pin value (+160 V on both the schematic and the layout page)"
      },
      "KAT": {
        "chart": 1.3,
        "tol_pct": 20,
        "note": "6AT6 cathode above the 1.5 k (25 uF bypass)"
      },
      "P2A": {
        "chart": 170,
        "tol_pct": 20,
        "note": "12AX7 driver plate"
      },
      "K2A": {
        "chart": 1.5,
        "tol_pct": 20,
        "note": "12AX7 driver cathode, unbypassed 1.5 k — printed on the same F-EF chart as the rest of this table. The 56 k negative-feedback resistor loads it at DC and the anchor-fit 12AX7 runs a little light here, so simulation sits below the printed figure; it stays inside the chart's own +/-20% convention and is gated like every other tube pin"
      },
      "PPI": {
        "chart": 207,
        "tol_pct": 20,
        "note": "cathodyne plate, 56 k load from +250"
      },
      "KPI": {
        "chart": 44.3,
        "tol_pct": 20,
        "note": "cathodyne cathode pin (top of the 1.5 k)"
      },
      "JPI": {
        "chart": 43,
        "tol_pct": 20,
        "note": "cathodyne junction (1.5 k / 56 k), grid-leak return"
      },
      "G6A": {
        "chart": -27,
        "tol_pct": 8,
        "note": "6V6 grids via 220k from the -27 V fixed-bias line (driven)"
      }
    }
  },
  "operatingPoint": [
    {
      "node": "BP2",
      "chart": 302,
      "sim": 302.936,
      "disputed": false,
      "dev_pct": 0.30993377483442996,
      "tol_pct": 8,
      "gated": true,
      "within": true,
      "note": "6V6 screen node, after the 470 ohm",
      "dispute_note": ""
    },
    {
      "node": "BP3",
      "chart": 250,
      "sim": 244.938,
      "disputed": false,
      "dev_pct": 2.024800000000005,
      "tol_pct": 8,
      "gated": true,
      "within": true,
      "note": "preamp/PI supply node, after the 22 k dropper",
      "dispute_note": ""
    },
    {
      "node": "PAT",
      "chart": 160,
      "sim": 151.242,
      "disputed": false,
      "dev_pct": 5.473750000000006,
      "tol_pct": 20,
      "gated": true,
      "within": true,
      "note": "6AT6 plate, printed pin value (+160 V on both the schematic and the layout page)",
      "dispute_note": ""
    },
    {
      "node": "KAT",
      "chart": 1.3,
      "sim": 1.405,
      "disputed": false,
      "dev_pct": 8.076923076923075,
      "tol_pct": 20,
      "gated": true,
      "within": true,
      "note": "6AT6 cathode above the 1.5 k (25 uF bypass)",
      "dispute_note": ""
    },
    {
      "node": "P2A",
      "chart": 170,
      "sim": 157.906,
      "disputed": false,
      "dev_pct": 7.114117647058819,
      "tol_pct": 20,
      "gated": true,
      "within": true,
      "note": "12AX7 driver plate",
      "dispute_note": ""
    },
    {
      "node": "K2A",
      "chart": 1.5,
      "sim": 1.271,
      "disputed": false,
      "dev_pct": 15.266666666666673,
      "tol_pct": 20,
      "gated": true,
      "within": true,
      "note": "12AX7 driver cathode, unbypassed 1.5 k — printed on the same F-EF chart as the rest of this table. The 56 k negative-feedback resistor loads it at DC and the anchor-fit 12AX7 runs a little light here, so simulation sits below the printed figure; it stays inside the chart's own +/-20% convention and is gated like every other tube pin",
      "dispute_note": ""
    },
    {
      "node": "PPI",
      "chart": 207,
      "sim": 198.517,
      "disputed": false,
      "dev_pct": 4.098067632850244,
      "tol_pct": 20,
      "gated": true,
      "within": true,
      "note": "cathodyne plate, 56 k load from +250",
      "dispute_note": ""
    },
    {
      "node": "KPI",
      "chart": 44.3,
      "sim": 47.665,
      "disputed": false,
      "dev_pct": 7.595936794582397,
      "tol_pct": 20,
      "gated": true,
      "within": true,
      "note": "cathodyne cathode pin (top of the 1.5 k)",
      "dispute_note": ""
    },
    {
      "node": "JPI",
      "chart": 43,
      "sim": 46.422,
      "disputed": false,
      "dev_pct": 7.958139534883714,
      "tol_pct": 20,
      "gated": true,
      "within": true,
      "note": "cathodyne junction (1.5 k / 56 k), grid-leak return",
      "dispute_note": ""
    },
    {
      "node": "G6A",
      "chart": -27,
      "sim": -27,
      "disputed": false,
      "dev_pct": 0,
      "tol_pct": 8,
      "gated": true,
      "within": true,
      "note": "6V6 grids via 220k from the -27 V fixed-bias line (driven)",
      "dispute_note": ""
    }
  ],
  "checks": [
    {
      "id": "dc",
      "title": "DC operating point",
      "status": "Verified",
      "summary": "10 reference nodes are within tolerance. Maintainer verification is recorded for 2026-07-18; 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.",
        "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.",
        "2 sheet-only parts are explicitly excluded: Rs1, Rs2. Heaters and the pilot lamp are checked separately."
      ],
      "tone": "checked"
    },
    {
      "id": "heaters",
      "title": "Heater and filament wiring",
      "status": "Checked",
      "summary": "The declared heater circuits cover the drawing and pass their separate wiring check.",
      "details": [],
      "tone": "checked"
    },
    {
      "id": "polarity",
      "title": "Capacitor polarity",
      "status": "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": "5f10-tone-network-2026-10-03",
      "date": "2026-10-03",
      "amps": [
        "5f10"
      ],
      "title": "5F10 tone control, bias filter and line capacitor",
      "description": "The tone control is now wired as the factory drawing shows, a single-knob blend whose wiper sits on the volume control's input, with 0.005 µF to ground from one end and 500 pF to the volume wiper from the other. The schematic and the board had each drawn it differently and both incorrectly. The bias supply has one 25 µF filter capacitor, the mains has one line capacitor, and the pilot bulb's type is no longer stated because the drawing does not print one. No operating point changes.",
      "commit": "1e464595da76c7c373a8c7cd4eb490e5f9a83d56",
      "url": "https://github.com/TheAnalogMaker/circuit-codex/commit/1e464595da76c7c373a8c7cd4eb490e5f9a83d56"
    }
  ],
  "sourceDirectory": "https://github.com/TheAnalogMaker/circuit-codex/tree/ebddc3fd2cf887dca010bbe60487d7391ea6c052/amps/5f10"
}