{
  "format": "circuit-codex-reference",
  "version": 1,
  "id": "5f2a",
  "url": "https://circuitcodex.com/amps/5f2a/",
  "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": "5f2a",
    "name_style": "Tweed Princeton-style",
    "family": "tweed",
    "era": {
      "start": 1957,
      "end": 1961
    },
    "wattage": 5,
    "tubes": [
      "12AX7",
      "6V6GT",
      "5Y3GT"
    ],
    "topology": {
      "rectifier": {
        "kind": "tube",
        "type": "5Y3GT"
      },
      "bias": "cathode",
      "phase_inverter": "none",
      "tone_stack": "single-knob"
    },
    "lineage": {
      "derived_from": [],
      "influenced": []
    },
    "conventions": {
      "designators": "sequential"
    },
    "sources": [
      {
        "desc": "Fender 'Princeton' Model 5F2-A drawing (K-EG), layout + schematic sheets: every component value read directly from the published drawing (2026-07-18) — two-jack input (68k stoppers, 1M leak), V1A 100k/1.5k-bypassed, the single tone/volume network (1M lin pots, 0.02/0.005/500 pF caps), V1B 100k with an UNbypassed 1.5k cathode carrying the 22k speaker feedback, 6V6GT 470 Ω · 1 W / 220 kΩ, and the 32 µF/8 µF/8 µF supply split by a 10 kΩ · 1 W and a 22k dropper (PT 66079, OT 265). The drawing prints no voltage chart. Not reproduced here; archived at EL34World",
        "url": "https://el34world.com/charts/Schematics/files/Fender/Fender_princeton_5f2a.pdf"
      },
      {
        "desc": "Rob Robinette, 'How Amps Work' (tweed 5F1/6V6 single-ended walkthrough) — published DC measurements used as the verification reference in lieu of a factory chart: B+ 360/325/250, 6V6 ~19 V cathode drop across 470R, 12AX7 plates ~170 V, cathodes ~1.5 V. The 5F2-A shares this circuit's DC signal path exactly (the tone control is capacitor-coupled)",
        "url": "https://robrobinette.com/How_Amps_Work.htm"
      },
      {
        "desc": "Fender 'Princeton' Model 5F2-A layout drawing (K-EG), page 1 — the source for the order the board-layout drawing on this page places parts on the eyelet board and for the socket/pot/jack wiring (5Y3GT and 6V6GT pin numbers read directly off the sheet; the 12AX7 socket is drawn with plain dots, so its pins follow the standard Fender A=6/7/8, B=1/2/3 convention). R3/R7/R12 mount standing at a jack/socket lug rather than on the strip, and the tone pot's C3/C4 mount at the pots — all wired but not drawn as board bodies, matching the sheet; the output transformer isn't drawn as its own symbol on this sheet either. Redrawn from the published facts, never traced",
        "url": "https://el34world.com/charts/Schematics/files/Fender/Fender_princeton_5f2a.pdf"
      }
    ],
    "verification": {
      "status": "draft"
    },
    "added": "2026-07-18T00:00:00.000Z",
    "contributors": [
      "TheAnalogMaker"
    ]
  },
  "parts": {
    "notes": "The 5F2-A has one channel across two input jacks (high/low), each with its own 68 kΩ stopper sharing the 1 MΩ leak. V1B's cathode is deliberately UNbypassed — the 22 kΩ feedback resistor from the speaker works against it. Power transformer is listed at the end without a designator; its HT winding voltage is not printed on the drawing.",
    "items": [
      {
        "ref": "R1",
        "part": "Carbon comp resistor",
        "value": "68 kΩ · ½ W",
        "role": "Input grid stopper, jack 1 (high)"
      },
      {
        "ref": "R2",
        "part": "Carbon comp resistor",
        "value": "68 kΩ · ½ W",
        "role": "Input grid stopper, jack 2 (low)"
      },
      {
        "ref": "R3",
        "part": "Carbon comp resistor",
        "value": "1 MΩ · ½ W",
        "role": "Input grid leak"
      },
      {
        "ref": "R4",
        "part": "Carbon comp resistor",
        "value": "100 kΩ · ½ W",
        "role": "V1A plate load"
      },
      {
        "ref": "R5",
        "part": "Carbon comp resistor",
        "value": "1.5 kΩ · ½ W",
        "role": "V1A cathode bias"
      },
      {
        "ref": "R6",
        "part": "Carbon comp resistor",
        "value": "100 kΩ · ½ W",
        "role": "V1B plate load"
      },
      {
        "ref": "R7",
        "part": "Carbon comp resistor",
        "value": "1.5 kΩ · ½ W",
        "role": "V1B cathode bias (unbypassed)"
      },
      {
        "ref": "R8",
        "part": "Carbon comp resistor",
        "value": "220 kΩ · ½ W",
        "role": "6V6 grid leak"
      },
      {
        "ref": "R9",
        "part": "Wirewound resistor",
        "value": "470 Ω · 1 W",
        "role": "6V6 cathode bias"
      },
      {
        "ref": "R10",
        "part": "Power resistor",
        "value": "10 kΩ · 1 W",
        "role": "Rail dropper B+1→B+2"
      },
      {
        "ref": "R11",
        "part": "Carbon comp resistor",
        "value": "22 kΩ · ½ W",
        "role": "Rail dropper B+2→B+3"
      },
      {
        "ref": "R12",
        "part": "Carbon comp resistor",
        "value": "22 kΩ · ½ W",
        "role": "Negative feedback, speaker→V1B cathode"
      },
      {
        "ref": "VR1",
        "part": "Linear-taper potentiometer",
        "value": "1 MΩ",
        "role": "Volume"
      },
      {
        "ref": "VR2",
        "part": "Linear-taper potentiometer",
        "value": "1 MΩ",
        "role": "Tone"
      },
      {
        "ref": "C1",
        "part": "Electrolytic capacitor",
        "value": "25 µF · 25 V",
        "role": "V1A cathode bypass"
      },
      {
        "ref": "C2",
        "part": "Coupling capacitor",
        "value": "0.02 µF · 400 V",
        "role": "V1A → tone/volume network"
      },
      {
        "ref": "C3",
        "part": "Mica capacitor",
        "value": "0.005 µF",
        "role": "Tone — treble shunt to ground"
      },
      {
        "ref": "C4",
        "part": "Mica capacitor",
        "value": "500 pF",
        "role": "Tone — network to V1B grid"
      },
      {
        "ref": "C5",
        "part": "Coupling capacitor",
        "value": "0.02 µF · 400 V",
        "role": "V1B → 6V6 grid"
      },
      {
        "ref": "C6",
        "part": "Electrolytic capacitor",
        "value": "25 µF · 25 V",
        "role": "6V6 cathode bypass"
      },
      {
        "ref": "C7",
        "part": "Electrolytic capacitor",
        "value": "16 µF · 450 V",
        "role": "Filter, B+1"
      },
      {
        "ref": "C8",
        "part": "Electrolytic capacitor",
        "value": "16 µF · 450 V",
        "role": "Filter, B+1 (paralleled)"
      },
      {
        "ref": "C9",
        "part": "Electrolytic capacitor",
        "value": "8 µF · 450 V",
        "role": "Filter, B+2"
      },
      {
        "ref": "C10",
        "part": "Electrolytic capacitor",
        "value": "8 µF · 450 V",
        "role": "Filter, B+3"
      },
      {
        "ref": "C11",
        "part": "Film capacitor",
        "value": "0.05 µF · 600 V",
        "role": "Across the AC line"
      },
      {
        "ref": "V1",
        "part": "Preamp tube",
        "value": "12AX7",
        "role": "Both gain stages (V1A/V1B)"
      },
      {
        "ref": "V2",
        "part": "Power tube",
        "value": "6V6GT",
        "role": "Single-ended output"
      },
      {
        "ref": "V3",
        "part": "Rectifier tube",
        "value": "5Y3GT",
        "role": "Full-wave rectifier (V3A/V3B)"
      },
      {
        "ref": "T2",
        "part": "Output transformer",
        "value": "≈ 5 kΩ : 8 Ω",
        "role": "Single-ended output (part 265; impedance not marked on the drawing; typical SE 6V6 load)"
      },
      {
        "ref": "—",
        "part": "Power transformer",
        "value": "HT c.t. · 6.3 V · 5 V",
        "role": "Part 66079; HT winding voltage not printed on the drawing"
      }
    ]
  },
  "publishedVoltages": {
    "source": "Rob Robinette 'How Amps Work' measured DC for the DC-identical tweed 6V6 SE circuit (B+ 360/325/250; 6V6 ~19 V cathode; 12AX7 plates ~170 V; cathodes ~1.5 V). B+1 driven at 360 V; downstream nodes derived.",
    "nodes": {
      "BP2": {
        "chart": 325,
        "tol_pct": 10,
        "note": "6V6 screen node, after the 10 kΩ dropper"
      },
      "BP3": {
        "chart": 250,
        "tol_pct": 10,
        "note": "preamp node, after the 22 kΩ dropper"
      },
      "P1A": {
        "chart": 170,
        "tol_pct": 20,
        "note": "V1A 12AX7 plate, reference pin value"
      },
      "P1B": {
        "chart": 170,
        "tol_pct": 20,
        "note": "V1B 12AX7 plate (22k feedback on its cathode)"
      },
      "K2": {
        "chart": 19,
        "tol_pct": 20,
        "note": "6V6GT cathode across 470 Ω 1 W"
      },
      "K1A": {
        "chart": null,
        "note": "informational — V1A cathode, ~1.5 V self-bias"
      },
      "K1B": {
        "chart": null,
        "note": "informational — V1B cathode; 22k speaker feedback parallels the 1.5k at DC"
      }
    }
  },
  "operatingPoint": [
    {
      "node": "BP2",
      "chart": 325,
      "sim": 308.791,
      "disputed": false,
      "dev_pct": 4.987384615384617,
      "tol_pct": 10,
      "gated": true,
      "within": true,
      "note": "6V6 screen node, after the 10 kΩ dropper",
      "dispute_note": ""
    },
    {
      "node": "BP3",
      "chart": 250,
      "sim": 267.249,
      "disputed": false,
      "dev_pct": 6.89960000000001,
      "tol_pct": 10,
      "gated": true,
      "within": true,
      "note": "preamp node, after the 22 kΩ dropper",
      "dispute_note": ""
    },
    {
      "node": "P1A",
      "chart": 170,
      "sim": 174.238,
      "disputed": false,
      "dev_pct": 2.492941176470588,
      "tol_pct": 20,
      "gated": true,
      "within": true,
      "note": "V1A 12AX7 plate, reference pin value",
      "dispute_note": ""
    },
    {
      "node": "P1B",
      "chart": 170,
      "sim": 171.431,
      "disputed": false,
      "dev_pct": 0.8417647058823597,
      "tol_pct": 20,
      "gated": true,
      "within": true,
      "note": "V1B 12AX7 plate (22k feedback on its cathode)",
      "dispute_note": ""
    },
    {
      "node": "K2",
      "chart": 19,
      "sim": 19.294,
      "disputed": false,
      "dev_pct": 1.5473684210526342,
      "tol_pct": 20,
      "gated": true,
      "within": true,
      "note": "6V6GT cathode across 470 Ω 1 W",
      "dispute_note": ""
    },
    {
      "node": "K1A",
      "chart": null,
      "sim": 1.395,
      "disputed": false,
      "dev_pct": null,
      "tol_pct": 5,
      "gated": false,
      "within": null,
      "note": "informational — V1A cathode, ~1.5 V self-bias",
      "dispute_note": ""
    },
    {
      "node": "K1B",
      "chart": null,
      "sim": 1.346,
      "disputed": false,
      "dev_pct": null,
      "tol_pct": 5,
      "gated": false,
      "within": null,
      "note": "informational — V1B cathode; 22k speaker feedback parallels the 1.5k at DC",
      "dispute_note": ""
    }
  ],
  "checks": [
    {
      "id": "dc",
      "title": "DC operating point",
      "status": "Within target",
      "summary": "5 reference nodes are within tolerance. The circuit remains a draft awaiting maintainer review.",
      "details": [
        "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": "Open findings",
      "summary": "2 merged nets.",
      "details": [
        "A finding identifies a difference or a coverage gap. The factory source must decide which drawing, if either, needs correction.",
        "3 sheet-only parts are explicitly excluded: C11, C3, C4. Heaters and the pilot lamp are checked separately."
      ],
      "tone": "attention"
    },
    {
      "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": "6 capacitor markings agree with the model's voltage ordering.",
      "details": [
        "This check uses DC voltage ordering; source review establishes markings the model cannot decide."
      ],
      "tone": "checked"
    }
  ],
  "corrections": [],
  "sourceDirectory": "https://github.com/TheAnalogMaker/circuit-codex/tree/ebddc3fd2cf887dca010bbe60487d7391ea6c052/amps/5f2a"
}