{
  "format": "circuit-codex-reference",
  "version": 1,
  "id": "b15n",
  "url": "https://circuitcodex.com/amps/b15n/",
  "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": "b15n",
    "name_style": "Ampeg B-15N Portaflex-style",
    "family": "other",
    "era": {
      "start": 1961,
      "end": 1964
    },
    "wattage": 25,
    "tubes": [
      "6SL7",
      "6SL7",
      "6SL7",
      "6L6GC",
      "6L6GC",
      "5AR4"
    ],
    "topology": {
      "rectifier": {
        "kind": "tube",
        "type": "5AR4"
      },
      "bias": "fixed",
      "phase_inverter": "paraphase",
      "tone_stack": "per-channel-tb"
    },
    "lineage": {
      "derived_from": [],
      "influenced": []
    },
    "conventions": {
      "notation": "us",
      "designators": "functional"
    },
    "sources": [
      {
        "desc": "Ampeg factory schematic, engineering issue — THIS is the revision documented here. Title block read from the sheet: \"B-15-N / U.S. PATENT 3183305 / TUBES / 6SL7 - 6SL7 - 6SL7 - 6L6GC - 6L6GC - 5AR4 / -472-\", with \"BY S.C. | 1268 | PART NO. 591722 | C\" beneath it and a revision block reading \"1/22/74 | C | 591722-2\" over \"B | 591722-1\"; the Ampeg roundel, POST OFFICE BOX 315, LINDEN, NEW JERSEY 07036. Sheet notes: \"1 ALL RESISTORS 1/2 W 10% UNLESS OTHERWISE SPECIFIED\", \"2 ALL CAPACITORS IN MFD & 400V UNLESS OTHERWISE SPECIFIED\", \"3 VOLTAGE READINGS ARE D.C. TAKEN WITH NO SIGNAL INSERTED USING A 20,000 Ω/VOLT METER\". Values read from the drawing: two identical channels, each a 6SL7 with a 470 kΩ anode load (annotated 165 V) over an unbypassed 5.6 kΩ cathode (2.2 V) into a 39 kΩ/1 MΩ ULTRA LO shelving network and a 1 MΩ linear volume with a 500 pF ULTRA HI bright cap, then a second 6SL7 section on 220 kΩ (175 V) over 2.2 kΩ (2 V) into a printed Bass/Treble board (220 kΩ series, 1 MΩ bass pot with 0.001 µF and 0.01 µF to its wiper over a 22 kΩ foot, 120 kΩ link, 470 pF into a 1 MΩ treble pot over a 0.0047 µF foot) and out through a 270 kΩ mixing resistor; a third 6SL7 as driver and self-balancing paraphase on two 120 kΩ anode loads (annotated 235 V and 225 V) with a 470 kΩ/510 kΩ divider across those two anodes feeding the second grid through 0.022 µF, a 220 Ω cathode taking 10 kΩ of negative feedback from the output transformer's green secondary lead and a 1 kΩ/25 µF cathode on the other half; 0.022 µF couplers and 1 kΩ stoppers to a 6L6GC pair whose grids return through 270 kΩ each to an annotated -50 V line and whose cathodes go straight to ground (annotated 450 V anodes, 445 V screens, no screen stoppers, no cathode resistor); OT-214 output transformer (the handwritten part number beside it is only partly legible on this scan), PT-108 power transformer (part 300708-1), a 5AR4 with a 30 µF · 600 V reservoir, a 1 kΩ · 10 W dropper to the screen node and two 22 kΩ · 1 W droppers off it to the preamp and driver rails, a three-section 40 µF · 500 V can, and a separate \"F-4\" diode bias supply. Not reproduced here.",
        "url": "https://ampeg.com/data/6/0a000509142f661ff65a5784a/application/pdf/"
      },
      {
        "desc": "Ampeg service-manual schematic sheet of the same revision, headed \"MODEL B15N SCHEMATIC DIAGRAM (REV. C)\" — the corroborating second reading. Same circuit, same annotated voltages, with the manual's own notes (\"1. Capacitance values are in microfarads, 10%, 400V\", \"2. Resistors are 1/2 W, 10%, composition\", \"3. D.C. voltage readings taken with no signal applied using a 20,000 ohm/volt voltmeter\", \"4. Actual circuit may vary slightly due to normal production changes\") and an A.C. VOLTAGE MEASUREMENTS table taken at \"INPUT: .3V A.C. 400/cps\" for \"OUTPUT: 11V A.C. across 8 ohms load\", with \"Bass and Treble controls at mid-position and ultra hi and ultra lo switches off\". Only the table's first two rows survive the page trim on the published scan: V1 and V2 (6SL7) read .65 V on pin 1, 19 V on pin 2, .29 V on pin 4 and 6.5 V on pin 5, pins 7 and 8 marked \"Fil.\". The two sheets agree on every component value and every D.C. annotation; where they differ is the bias-supply corner, and the difference is recorded in the circuit story.",
        "url": "https://ampeg.com/data/6/0a0005091412661ff665e83fe/application/pdf/"
      },
      {
        "desc": "Wikipedia, \"Ampeg Portaflex\" — the model chronology behind this entry's era bracket and its 25 W rating: the 1960 B-15 \"was replaced by the B-15N in 1961\", and the line's 1962 update fitted \"a solid-state rectifier called the B-15NB\".",
        "url": "https://en.wikipedia.org/wiki/Ampeg_Portaflex"
      },
      {
        "desc": "RCA 6SL7-GT data sheet, November 5, 1954 — the anchor behind the clean-room 6SL7GT model this circuit's five triode sections are simulated on: Amplifier Class A1, Va=250 V, Vg=-2 V → Ia=2.3 mA, rp=44 kΩ, gm=1600 µmho, µ=70, with a 1 W plate dissipation and a 300 V plate ceiling per unit. Basing 8BD, which is what makes the drawing's pin numbers readable: pins 1/2/3 are grid, plate and cathode of unit 2 and pins 4/5/6 the same of unit 1. See the 6SL7GT reference page for the model and its method.",
        "url": "https://frank.pocnet.net/sheets/049/6/6SL7GT.pdf"
      },
      {
        "desc": "RCA 6L6-GC data sheet, DATA 1, 8-60 — the anchor behind the clean-room 6L6GC output model: Class A1 Va=250 V, Vg2=250 V, Vg1=-14 V → Ia=72 mA, Ig2=5 mA, gm=6000 µmho, design-maximum 30 W plate, 500 V plate, 450 V screen. The 450 V/445 V this drawing annotates sits inside that envelope, which is the reason the Portaflex could run the rail it does. See the 6L6GC reference page.",
        "url": "https://frank.pocnet.net/sheets/049/6/6L6GC.pdf"
      }
    ],
    "verification": {
      "status": "draft"
    },
    "added": "2026-08-30T00:00:00.000Z",
    "contributors": [
      "TheAnalogMaker"
    ]
  },
  "parts": {
    "notes": "DESIGNATORS. This sheet letters most of what it draws — R1…R42, C1…C20, VR1…VR7, SW1…SW7, J1…J6, V1…V6 and D1 — and those numbers are kept exactly. Three groups of parts have no usable factory designator and carry role codes instead, which is why the list as a whole reads as a functional one. (1) The two printed tone boards. Each is drawn inside a dashed outline with a P.E.C. number beside it — the channel-2 board reads 250762-1; the channel-1 number is smudged on this scan — and six of the parts inside each outline are drawn with a value and no designator at all, even though R17/R21 and the two pots inside the same outline are lettered. Those twelve get RTA*/CTA* (channel 1) and RTB*/CTB* (channel 2). (2) The driver's 25 µF · 25 V cathode bypass, drawn beside R24 with no number: CKD1. (3) TWO CAPACITORS THE SHEET LETTERS C19 A SECOND AND THIRD TIME. The drawing uses the designator C19 for three different parts: channel 1's 0.01 µF coupler into the volume pot, a 10 µF · 100 V electrolytic in the bias supply, and one of the two 0.047 µF · 600 V capacitors across the mains switching. C19 is kept for the first of them, in reading order across the sheet; the other two are listed as CBF2 and CM2, each saying in its role that the factory number is C19. A parts list cannot carry one designator three times, and silently renumbering a factory sheet would hide a fact a builder holding the drawing needs to know. (4) THE THREE-SECTION CAN. The sheet rings three 40 µF · 500 V sections in one dashed outline and letters the outline C16. Its three sections sit on three different nodes — the screen node, the preamp rail and the driver rail — so they are listed as C16A, C16B and C16C, each stating its own section's value with the packaging named in its role. One designator cannot be carried on three different nodes.",
    "items": [
      {
        "ref": "J1",
        "part": "Jack socket",
        "value": "1/4 in",
        "role": "Channel 1 input, panel-marked BRIGHT"
      },
      {
        "ref": "J2",
        "part": "Jack socket",
        "value": "1/4 in",
        "role": "Channel 1 input, panel-marked NORMAL"
      },
      {
        "ref": "R1",
        "part": "Carbon comp resistor",
        "value": "100 kΩ",
        "role": "Channel 1 BRIGHT jack series resistor, into V1 pin 4"
      },
      {
        "ref": "C1",
        "part": "Coupling capacitor",
        "value": "0.005 µF",
        "role": "Bridges R1 — the BRIGHT jack's high-frequency bypass"
      },
      {
        "ref": "R2",
        "part": "Carbon comp resistor",
        "value": "47 kΩ",
        "role": "Channel 1 NORMAL jack series resistor, into the same grid"
      },
      {
        "ref": "R5",
        "part": "Carbon comp resistor",
        "value": "5.6 MΩ",
        "role": "Channel 1 input grid leak"
      },
      {
        "ref": "R7",
        "part": "Carbon comp resistor",
        "value": "470 kΩ",
        "role": "V1 unit 1 anode load (pin 5)"
      },
      {
        "ref": "R8",
        "part": "Carbon comp resistor",
        "value": "5.6 kΩ",
        "role": "V1 unit 1 cathode bias (pin 6) — unbypassed"
      },
      {
        "ref": "C3",
        "part": "Coupling capacitor",
        "value": "0.1 µF",
        "role": "V1 unit 1 anode coupler into the channel-1 ULTRA network"
      },
      {
        "ref": "C4",
        "part": "Coupling capacitor",
        "value": "0.02 µF",
        "role": "Channel 1 ULTRA LO shunt capacitor"
      },
      {
        "ref": "R9",
        "part": "Carbon comp resistor",
        "value": "39 kΩ",
        "role": "Channel 1 ULTRA LO series resistor, under C4"
      },
      {
        "ref": "R10",
        "part": "Carbon comp resistor",
        "value": "1 MΩ",
        "role": "Channel 1 ULTRA LO shunt resistor, shorted out by SW2"
      },
      {
        "ref": "SW2",
        "part": "Toggle switch",
        "value": "SPST",
        "role": "Channel 1 ULTRA LO — grounds the foot of R9, taking R10 out"
      },
      {
        "ref": "C19",
        "part": "Coupling capacitor",
        "value": "0.01 µF",
        "role": "Channel 1 coupler into the volume pot. NOTE: the sheet letters two other parts C19 as well — see notes above"
      },
      {
        "ref": "VR1",
        "part": "Linear potentiometer",
        "value": "1 MΩ-L",
        "role": "Channel 1 volume; also V1 unit 2's only DC grid return"
      },
      {
        "ref": "C9",
        "part": "Mica capacitor",
        "value": "500 pF",
        "role": "Channel 1 bright cap, top of VR1 to its wiper through SW1"
      },
      {
        "ref": "SW1",
        "part": "Toggle switch",
        "value": "SPST",
        "role": "Channel 1 ULTRA HI — switches C9 across the volume pot"
      },
      {
        "ref": "R15",
        "part": "Carbon comp resistor",
        "value": "220 kΩ",
        "role": "V1 unit 2 anode load (pin 2)"
      },
      {
        "ref": "R16",
        "part": "Carbon comp resistor",
        "value": "2.2 kΩ",
        "role": "V1 unit 2 cathode bias (pin 3) — unbypassed"
      },
      {
        "ref": "C10",
        "part": "Coupling capacitor",
        "value": "0.1 µF",
        "role": "V1 unit 2 anode coupler into the channel-1 tone board"
      },
      {
        "ref": "RTA1",
        "part": "Carbon comp resistor",
        "value": "220 kΩ",
        "role": "Channel 1 tone board: series resistor from the board input to the bass pot. Unlettered on the drawing"
      },
      {
        "ref": "VR2",
        "part": "Audio-taper potentiometer",
        "value": "1 MΩ-A",
        "role": "Channel 1 bass"
      },
      {
        "ref": "CTA1",
        "part": "Mica capacitor",
        "value": "0.001 µF",
        "role": "Channel 1 tone board: bass pot top lug to wiper. Unlettered"
      },
      {
        "ref": "CTA2",
        "part": "Coupling capacitor",
        "value": "0.01 µF",
        "role": "Channel 1 tone board: bass pot bottom lug to wiper. Unlettered"
      },
      {
        "ref": "RTA2",
        "part": "Carbon comp resistor",
        "value": "22 kΩ",
        "role": "Channel 1 tone board: bass pot foot to ground. Unlettered"
      },
      {
        "ref": "R17",
        "part": "Carbon comp resistor",
        "value": "120 kΩ",
        "role": "Channel 1 tone board link — bass wiper to the treble wiper, which is the board's output"
      },
      {
        "ref": "CTA3",
        "part": "Mica capacitor",
        "value": "470 pF",
        "role": "Channel 1 tone board: board input to the treble pot top lug. Unlettered"
      },
      {
        "ref": "VR3",
        "part": "Audio-taper potentiometer",
        "value": "1 MΩ-A",
        "role": "Channel 1 treble; its wiper is the board output"
      },
      {
        "ref": "CTA4",
        "part": "Coupling capacitor",
        "value": "0.0047 µF",
        "role": "Channel 1 tone board: treble pot foot to ground. Unlettered"
      },
      {
        "ref": "R18",
        "part": "Carbon comp resistor",
        "value": "270 kΩ",
        "role": "Channel 1 mixing resistor into the driver grid"
      },
      {
        "ref": "J3",
        "part": "Jack socket",
        "value": "1/4 in",
        "role": "Channel 2 input, panel-marked BRIGHT"
      },
      {
        "ref": "J4",
        "part": "Jack socket",
        "value": "1/4 in",
        "role": "Channel 2 input, panel-marked NORMAL"
      },
      {
        "ref": "R3",
        "part": "Carbon comp resistor",
        "value": "100 kΩ",
        "role": "Channel 2 BRIGHT jack series resistor"
      },
      {
        "ref": "C2",
        "part": "Coupling capacitor",
        "value": "0.005 µF",
        "role": "Bridges R3"
      },
      {
        "ref": "R4",
        "part": "Carbon comp resistor",
        "value": "47 kΩ",
        "role": "Channel 2 NORMAL jack series resistor"
      },
      {
        "ref": "R6",
        "part": "Carbon comp resistor",
        "value": "5.6 MΩ",
        "role": "Channel 2 input grid leak"
      },
      {
        "ref": "R11",
        "part": "Carbon comp resistor",
        "value": "470 kΩ",
        "role": "V2 unit 1 anode load"
      },
      {
        "ref": "R12",
        "part": "Carbon comp resistor",
        "value": "5.6 kΩ",
        "role": "V2 unit 1 cathode bias — unbypassed"
      },
      {
        "ref": "C5",
        "part": "Coupling capacitor",
        "value": "0.1 µF",
        "role": "V2 unit 1 anode coupler into the channel-2 ULTRA network"
      },
      {
        "ref": "C6",
        "part": "Coupling capacitor",
        "value": "0.02 µF",
        "role": "Channel 2 ULTRA LO shunt capacitor"
      },
      {
        "ref": "R13",
        "part": "Carbon comp resistor",
        "value": "39 kΩ",
        "role": "Channel 2 ULTRA LO series resistor"
      },
      {
        "ref": "R14",
        "part": "Carbon comp resistor",
        "value": "1 MΩ",
        "role": "Channel 2 ULTRA LO shunt resistor, shorted out by SW4"
      },
      {
        "ref": "SW4",
        "part": "Toggle switch",
        "value": "SPST",
        "role": "Channel 2 ULTRA LO"
      },
      {
        "ref": "C20",
        "part": "Coupling capacitor",
        "value": "0.01 µF",
        "role": "Channel 2 coupler into the volume pot"
      },
      {
        "ref": "VR4",
        "part": "Linear potentiometer",
        "value": "1 MΩ-L",
        "role": "Channel 2 volume; also V2 unit 2's only DC grid return"
      },
      {
        "ref": "C7",
        "part": "Mica capacitor",
        "value": "500 pF",
        "role": "Channel 2 bright cap, through SW3"
      },
      {
        "ref": "SW3",
        "part": "Toggle switch",
        "value": "SPST",
        "role": "Channel 2 ULTRA HI"
      },
      {
        "ref": "R19",
        "part": "Carbon comp resistor",
        "value": "220 kΩ",
        "role": "V2 unit 2 anode load"
      },
      {
        "ref": "R20",
        "part": "Carbon comp resistor",
        "value": "2.2 kΩ",
        "role": "V2 unit 2 cathode bias — unbypassed"
      },
      {
        "ref": "C8",
        "part": "Coupling capacitor",
        "value": "0.1 µF",
        "role": "V2 unit 2 anode coupler into the channel-2 tone board"
      },
      {
        "ref": "RTB1",
        "part": "Carbon comp resistor",
        "value": "220 kΩ",
        "role": "Channel 2 tone board (P.E.C. 250762-1): series resistor to the bass pot. Unlettered"
      },
      {
        "ref": "VR5",
        "part": "Audio-taper potentiometer",
        "value": "1 MΩ-A",
        "role": "Channel 2 bass"
      },
      {
        "ref": "CTB1",
        "part": "Mica capacitor",
        "value": "0.001 µF",
        "role": "Channel 2 tone board: bass pot top lug to wiper. Unlettered"
      },
      {
        "ref": "CTB2",
        "part": "Coupling capacitor",
        "value": "0.01 µF",
        "role": "Channel 2 tone board: bass pot bottom lug to wiper. Unlettered"
      },
      {
        "ref": "RTB2",
        "part": "Carbon comp resistor",
        "value": "22 kΩ",
        "role": "Channel 2 tone board: bass pot foot to ground. Unlettered"
      },
      {
        "ref": "R21",
        "part": "Carbon comp resistor",
        "value": "120 kΩ",
        "role": "Channel 2 tone board link — bass wiper to treble wiper"
      },
      {
        "ref": "CTB3",
        "part": "Mica capacitor",
        "value": "470 pF",
        "role": "Channel 2 tone board: board input to treble pot top lug. Unlettered"
      },
      {
        "ref": "VR6",
        "part": "Audio-taper potentiometer",
        "value": "1 MΩ-A",
        "role": "Channel 2 treble; its wiper is the board output"
      },
      {
        "ref": "CTB4",
        "part": "Coupling capacitor",
        "value": "0.0047 µF",
        "role": "Channel 2 tone board: treble pot foot to ground. Unlettered"
      },
      {
        "ref": "R22",
        "part": "Carbon comp resistor",
        "value": "270 kΩ",
        "role": "Channel 2 mixing resistor into the driver grid"
      },
      {
        "ref": "J5",
        "part": "Jack socket",
        "value": "1/4 in",
        "role": "EXT. AMP. output jack, tapping the channel mixing bus at the driver grid"
      },
      {
        "ref": "R26",
        "part": "Carbon comp resistor",
        "value": "120 kΩ",
        "role": "V3 unit 2 anode load (pin 2) — the driver half"
      },
      {
        "ref": "R25",
        "part": "Carbon comp resistor",
        "value": "220 Ω",
        "role": "V3 unit 2 cathode (pin 3), unbypassed"
      },
      {
        "ref": "R40",
        "part": "Carbon comp resistor",
        "value": "10 kΩ",
        "role": "Global negative feedback, output transformer green secondary lead back to V3 pin 1, the driver grid and channel mixing bus"
      },
      {
        "ref": "R27",
        "part": "Carbon comp resistor",
        "value": "120 kΩ",
        "role": "V3 unit 1 anode load (pin 5) — the inverted half"
      },
      {
        "ref": "R24",
        "part": "Carbon comp resistor",
        "value": "1 kΩ",
        "role": "V3 unit 1 cathode bias (pin 6)"
      },
      {
        "ref": "CKD1",
        "part": "Electrolytic capacitor",
        "value": "25 µF · 25 V",
        "role": "V3 unit 1 cathode bypass, across R24. Unlettered on the drawing"
      },
      {
        "ref": "R23",
        "part": "Carbon comp resistor",
        "value": "470 kΩ",
        "role": "V3 unit 1 grid leak (pin 4)"
      },
      {
        "ref": "R28",
        "part": "Carbon comp resistor",
        "value": "470 kΩ",
        "role": "Paraphase divider, V3 pin 2 anode to the tap"
      },
      {
        "ref": "R29",
        "part": "Carbon comp resistor",
        "value": "510 kΩ",
        "role": "Paraphase divider, tap to V3 pin 5 anode. R28 and R29 span the two driver anodes; their midpoint is the inverter"
      },
      {
        "ref": "C11",
        "part": "Coupling capacitor",
        "value": "0.022 µF",
        "role": "Paraphase tap to V3 unit 1's grid"
      },
      {
        "ref": "C13",
        "part": "Coupling capacitor",
        "value": "0.022 µF",
        "role": "V3 pin 2 to V5's grid line"
      },
      {
        "ref": "R33",
        "part": "Carbon comp resistor",
        "value": "1 kΩ",
        "role": "V5 grid stopper"
      },
      {
        "ref": "R30",
        "part": "Carbon comp resistor",
        "value": "270 kΩ",
        "role": "V5 grid return to the -50 V bias line"
      },
      {
        "ref": "C14",
        "part": "Coupling capacitor",
        "value": "0.022 µF",
        "role": "V3 pin 5 to V4's grid line"
      },
      {
        "ref": "R32",
        "part": "Carbon comp resistor",
        "value": "1 kΩ",
        "role": "V4 grid stopper"
      },
      {
        "ref": "R31",
        "part": "Carbon comp resistor",
        "value": "270 kΩ",
        "role": "V4 grid return to the -50 V bias line"
      },
      {
        "ref": "J6",
        "part": "Jack socket",
        "value": "1/4 in",
        "role": "EXT. SPKR. jack, normalling the internal speaker"
      },
      {
        "ref": "R41",
        "part": "Wirewound resistor",
        "value": "250 Ω · 10 W",
        "role": "Load resistor across the output-transformer secondary"
      },
      {
        "ref": "C17",
        "part": "Electrolytic capacitor",
        "value": "30 µF · 600 V",
        "role": "Reservoir — the 5AR4 cathode node, which is also the OT-214 primary centre tap and the 6L6GC anode node"
      },
      {
        "ref": "R39",
        "part": "Wirewound resistor",
        "value": "1 kΩ · 10 W · 5%",
        "role": "Reservoir to the 6L6GC screen node"
      },
      {
        "ref": "R37",
        "part": "Carbon comp resistor",
        "value": "22 kΩ · 1 W",
        "role": "Screen node to the preamp rail both channels share"
      },
      {
        "ref": "R38",
        "part": "Carbon comp resistor",
        "value": "22 kΩ · 1 W",
        "role": "Screen node to the driver rail feeding R26 and R27"
      },
      {
        "ref": "C16A",
        "part": "Electrolytic capacitor",
        "value": "40 µF · 500 V",
        "role": "Screen-node filter — one section of the three-section can the sheet letters C16"
      },
      {
        "ref": "C16B",
        "part": "Electrolytic capacitor",
        "value": "40 µF · 500 V",
        "role": "Preamp-rail filter — the second section of the C16 can"
      },
      {
        "ref": "C16C",
        "part": "Electrolytic capacitor",
        "value": "40 µF · 500 V",
        "role": "Driver-rail filter — the third section of the C16 can"
      },
      {
        "ref": "D1",
        "part": "Rectifier (bias)",
        "value": "F-4",
        "role": "Bias-supply rectifier, lettered F-4 on both cited sheets (no material printed)"
      },
      {
        "ref": "R36",
        "part": "Carbon comp resistor",
        "value": "100 kΩ · 2 W · 5%",
        "role": "Bias-supply feed resistor, between the bias line and the rectifier corner"
      },
      {
        "ref": "R34",
        "part": "Carbon comp resistor",
        "value": "47 kΩ · 5%",
        "role": "Bias-supply divider"
      },
      {
        "ref": "R35",
        "part": "Carbon comp resistor",
        "value": "56 kΩ · 5%",
        "role": "Bias-supply divider"
      },
      {
        "ref": "R42",
        "part": "Carbon comp resistor",
        "value": "10 kΩ",
        "role": "Bias-line decoupling resistor between the two 10 µF cans"
      },
      {
        "ref": "C15",
        "part": "Electrolytic capacitor",
        "value": "10 µF · 100 V",
        "role": "Bias-line filter"
      },
      {
        "ref": "CBF2",
        "part": "Electrolytic capacitor",
        "value": "10 µF · 100 V",
        "role": "Bias-line filter, the far side of R42. The sheet letters this C19, its second use of that number"
      },
      {
        "ref": "V1",
        "part": "Tube",
        "value": "6SL7",
        "role": "Channel 1, both triode sections"
      },
      {
        "ref": "V2",
        "part": "Tube",
        "value": "6SL7",
        "role": "Channel 2, both triode sections"
      },
      {
        "ref": "V3",
        "part": "Tube",
        "value": "6SL7",
        "role": "Driver and self-balancing paraphase inverter, both sections"
      },
      {
        "ref": "V4",
        "part": "Tube",
        "value": "6L6GC",
        "role": "Output, one half of the push-pull pair"
      },
      {
        "ref": "V5",
        "part": "Tube",
        "value": "6L6GC",
        "role": "Output, the other half"
      },
      {
        "ref": "V6",
        "part": "Rectifier tube",
        "value": "5AR4",
        "role": "Full-wave rectifier"
      },
      {
        "ref": "T1",
        "part": "Power transformer",
        "value": "Ampeg PT-108 (300708-1)",
        "role": "Mains transformer — centre-tapped HT winding, 5 V rectifier winding, 6.3 V heater winding. The drawing prints the part number and no winding voltages"
      },
      {
        "ref": "T2",
        "part": "Output transformer",
        "value": "Ampeg OT-214",
        "role": "Push-pull 6L6GC output, centre-tapped primary (blue/red/brown), tapped secondary (green/yellow/black); the handwritten part number beside it is only partly legible on this scan"
      },
      {
        "ref": "VR7",
        "part": "Linear potentiometer",
        "value": "100 Ω-L",
        "role": "HUM CONT. — heater hum balance across the 6.3 V line"
      },
      {
        "ref": "SW5",
        "part": "Toggle switch",
        "value": "SPST",
        "role": "STANDBY"
      },
      {
        "ref": "SW6",
        "part": "Toggle switch",
        "value": "SPST",
        "role": "POWER"
      },
      {
        "ref": "SW7",
        "part": "Toggle switch",
        "value": "SPDT",
        "role": "POLAR. — mains polarity"
      },
      {
        "ref": "C18",
        "part": "Coupling capacitor",
        "value": "0.047 µF · 600 V",
        "role": "Mains-side capacitor"
      },
      {
        "ref": "CM2",
        "part": "Coupling capacitor",
        "value": "0.047 µF · 600 V",
        "role": "Mains-side capacitor, the pair to C18. The sheet letters this C19 as well, its third use of that number"
      },
      {
        "ref": "—",
        "part": "Speaker",
        "value": "8 Ω",
        "role": "Internal speaker (annotation only — the drawing marks it 8 OHMS SPKR. and gives no size)"
      },
      {
        "ref": "—",
        "part": "Pilot lamp",
        "value": "mains",
        "role": "Panel pilot, drawn P.L. straight across the power transformer's mains primary, downstream of the POWER switch — not on the 6.3 V heater chain. The sheet gives no lamp type or rating (annotation only)"
      },
      {
        "ref": "—",
        "part": "Fuse",
        "value": "3 A",
        "role": "Mains fuse (annotation only)"
      },
      {
        "ref": "—",
        "part": "Fuse",
        "value": "6 A",
        "role": "Fuse on the switched AC outlet (annotation only)"
      },
      {
        "ref": "—",
        "part": "AC outlet",
        "value": "120 V · 500 W",
        "role": "Switched convenience outlet on the rear (annotation only)"
      }
    ]
  },
  "publishedVoltages": {
    "source": "Ampeg B-15N factory schematic, revision C (part 591722), voltages annotated beside the circuit: 165 V / 2.2 V and 175 V / 2 V at each channel's two 6SL7 stages; 235 V / 3 V and 225 V / 2.2 V at the 6SL7 driver; 450 V at both 6L6GC anodes, 445 V at their screens, -50 V at the fixed-bias line. Sheet note: 'VOLTAGE READINGS ARE D.C. TAKEN WITH NO SIGNAL INSERTED USING A 20,000 Ω/VOLT METER'. The service-manual sheet (REV. C) prints the same figures.",
    "nodes": {
      "BP2": {
        "chart": 445,
        "tol_pct": 8,
        "note": "6L6GC screen node — the 40 µF can after the 1 kΩ · 10 W dropper R39. The 5 V the drawing puts between plates and screens is about 5 mA through that dropper, which is what a 6L6GC pair idles at; the screens carry no stoppers of their own"
      },
      "P1A": {
        "chart": 165,
        "tol_pct": 20,
        "note": "channel 1, first 6SL7 stage (pin 5) — 470 kΩ load off the preamp rail"
      },
      "K1A": {
        "chart": 2.2,
        "tol_pct": 20,
        "note": "channel 1, first stage cathode (pin 6) over 5.6 kΩ, no bypass can anywhere in either channel's first stage"
      },
      "P1B": {
        "chart": 175,
        "tol_pct": 20,
        "note": "channel 1, second 6SL7 stage (pin 2) — 220 kΩ load, grid off the volume wiper"
      },
      "K1B": {
        "chart": 2,
        "tol_pct": 20,
        "note": "channel 1, second stage cathode (pin 3) over 2.2 kΩ, also unbypassed"
      },
      "P2A": {
        "chart": 165,
        "tol_pct": 20,
        "note": "channel 2, first stage — component-for-component identical to channel 1, and the drawing prints the same figures"
      },
      "K2A": {
        "chart": 2.2,
        "tol_pct": 20,
        "note": "channel 2, first stage cathode over 5.6 kΩ"
      },
      "P2B": {
        "chart": 175,
        "tol_pct": 20,
        "note": "channel 2, second stage — 220 kΩ load"
      },
      "K2B": {
        "chart": 2,
        "tol_pct": 20,
        "note": "channel 2, second stage cathode over 2.2 kΩ"
      },
      "P3A": {
        "chart": 225,
        "tol_pct": 20,
        "note": "driver V3 unit 1 (pin 5), the paraphase-inverted half — 120 kΩ load off the driver rail. Its own cathode figure is disputed below, so read this one as what it is: the printed anode voltage, which the circuit reproduces inside the era's tolerance while the cathode beside it cannot be true"
      },
      "P3B": {
        "chart": 235,
        "disputed": true,
        "dispute_note": "Driver V3 unit 2 (pin 2), the half the channels feed and the half the 10 kΩ feedback resistor lands under. Its printed 235 V and the 3 V printed at the cathode below it are two statements about one current and they disagree by more than a factor of ten. 235 V behind the drawn 120 kΩ load is 1.3 mA from a ~390 V rail, which over the drawn 220 Ω cathode resistor would read 0.29 V, not 3 V; conversely 3 V over 220 Ω is 13.6 mA, which through 120 kΩ is a 1636 V drop. Neither can be reconciled by any reading of the supply, because the amplifier's highest node is the 450 V reservoir. Simulated with the drawn values the stage settles near 138 V with 0.42 V on its cathode: the 220 Ω leaves the section almost unbiased, so it runs hot and its anode sits low. That is what the drawn parts do; the pair of figures printed beside them is recorded here and left standing."
      },
      "K3B": {
        "chart": 3,
        "disputed": true,
        "dispute_note": "Same node pair, taken from the cathode side. 3 V across R25's 220 Ω is 13.6 mA — six times the 2.3 mA the 6SL7 data sheet gives for its Class-A point, and 3.2 W dissipated in a plate rated 1 W. R25 is the stage's own unbypassed cathode resistor and nothing else lands on this node: the global feedback resistor R40 returns to the driver's grid (the channel mixing bus), not here, so no second path adds or removes cathode current. There is no reading of this sheet under which 3 V appears here."
      },
      "K3A": {
        "chart": 2.2,
        "disputed": true,
        "dispute_note": "Driver V3 unit 1's cathode (pin 6) over R24 1 kΩ, bypassed by 25 µF. 2.2 V is 2.2 mA; 2.2 mA through the drawn 120 kΩ anode load is a 264 V drop, so the 225 V printed at the anode above it would require a 489 V supply. The amplifier's highest node is the 450 V reservoir, and the driver rail sits below it behind R38's 22 kΩ. The stage simulates at 1.47 V with the drawn values, which is 33 % below the printed figure — outside the era's ±20 % — while the anode it feeds lands inside. The contradiction is the sheet's, not the model's, and it is left visible."
      },
      "BP3": {
        "chart": null,
        "note": "informational — the preamp rail both channels share, after R37's 22 kΩ from the screen node (40 µF can). The drawing prints no figure for it"
      },
      "BP4": {
        "chart": null,
        "note": "informational — the driver rail, after R38's 22 kΩ from the same screen node (40 µF can). Also unprinted. R37 and R38 leave the screen node together and never rejoin: the sheet's own hop-overs put each on its own horizontal"
      },
      "NPP": {
        "chart": null,
        "note": "informational — the paraphase tap itself, the midpoint of R28 470 kΩ and R29 510 kΩ strung across the two driver anodes. It is the whole inverter: it sees the two plates' antiphase swings and feeds the residual to the second grid through C11. No DC path leaves it except through that coupler, so its idle voltage is fixed entirely by the two plates it divides"
      }
    }
  },
  "operatingPoint": [
    {
      "node": "BP2",
      "chart": 445,
      "sim": 442.24,
      "disputed": false,
      "dev_pct": 0.6202247191011215,
      "tol_pct": 8,
      "gated": true,
      "within": true,
      "note": "6L6GC screen node — the 40 µF can after the 1 kΩ · 10 W dropper R39. The 5 V the drawing puts between plates and screens is about 5 mA through that dropper, which is what a 6L6GC pair idles at; the screens carry no stoppers of their own",
      "dispute_note": ""
    },
    {
      "node": "P1A",
      "chart": 165,
      "sim": 181.027,
      "disputed": false,
      "dev_pct": 9.713333333333326,
      "tol_pct": 20,
      "gated": true,
      "within": true,
      "note": "channel 1, first 6SL7 stage (pin 5) — 470 kΩ load off the preamp rail",
      "dispute_note": ""
    },
    {
      "node": "K1A",
      "chart": 2.2,
      "sim": 2.417,
      "disputed": false,
      "dev_pct": 9.863636363636347,
      "tol_pct": 20,
      "gated": true,
      "within": true,
      "note": "channel 1, first stage cathode (pin 6) over 5.6 kΩ, no bypass can anywhere in either channel's first stage",
      "dispute_note": ""
    },
    {
      "node": "P1B",
      "chart": 175,
      "sim": 187.263,
      "disputed": false,
      "dev_pct": 7.007428571428574,
      "tol_pct": 20,
      "gated": true,
      "within": true,
      "note": "channel 1, second 6SL7 stage (pin 2) — 220 kΩ load, grid off the volume wiper",
      "dispute_note": ""
    },
    {
      "node": "K1B",
      "chart": 2,
      "sim": 1.967,
      "disputed": false,
      "dev_pct": 1.649999999999996,
      "tol_pct": 20,
      "gated": true,
      "within": true,
      "note": "channel 1, second stage cathode (pin 3) over 2.2 kΩ, also unbypassed",
      "dispute_note": ""
    },
    {
      "node": "P2A",
      "chart": 165,
      "sim": 181.027,
      "disputed": false,
      "dev_pct": 9.713333333333326,
      "tol_pct": 20,
      "gated": true,
      "within": true,
      "note": "channel 2, first stage — component-for-component identical to channel 1, and the drawing prints the same figures",
      "dispute_note": ""
    },
    {
      "node": "K2A",
      "chart": 2.2,
      "sim": 2.417,
      "disputed": false,
      "dev_pct": 9.863636363636347,
      "tol_pct": 20,
      "gated": true,
      "within": true,
      "note": "channel 2, first stage cathode over 5.6 kΩ",
      "dispute_note": ""
    },
    {
      "node": "P2B",
      "chart": 175,
      "sim": 187.263,
      "disputed": false,
      "dev_pct": 7.007428571428574,
      "tol_pct": 20,
      "gated": true,
      "within": true,
      "note": "channel 2, second stage — 220 kΩ load",
      "dispute_note": ""
    },
    {
      "node": "K2B",
      "chart": 2,
      "sim": 1.967,
      "disputed": false,
      "dev_pct": 1.649999999999996,
      "tol_pct": 20,
      "gated": true,
      "within": true,
      "note": "channel 2, second stage cathode over 2.2 kΩ",
      "dispute_note": ""
    },
    {
      "node": "P3A",
      "chart": 225,
      "sim": 185.509,
      "disputed": false,
      "dev_pct": 17.551555555555563,
      "tol_pct": 20,
      "gated": true,
      "within": true,
      "note": "driver V3 unit 1 (pin 5), the paraphase-inverted half — 120 kΩ load off the driver rail. Its own cathode figure is disputed below, so read this one as what it is: the printed anode voltage, which the circuit reproduces inside the era's tolerance while the cathode beside it cannot be true",
      "dispute_note": ""
    },
    {
      "node": "P3B",
      "chart": 235,
      "sim": 138.918,
      "disputed": true,
      "dev_pct": 40.885957446808504,
      "tol_pct": 5,
      "gated": false,
      "within": null,
      "note": "",
      "dispute_note": "Driver V3 unit 2 (pin 2), the half the channels feed and the half the 10 kΩ feedback resistor lands under. Its printed 235 V and the 3 V printed at the cathode below it are two statements about one current and they disagree by more than a factor of ten. 235 V behind the drawn 120 kΩ load is 1.3 mA from a ~390 V rail, which over the drawn 220 Ω cathode resistor would read 0.29 V, not 3 V; conversely 3 V over 220 Ω is 13.6 mA, which through 120 kΩ is a 1636 V drop. Neither can be reconciled by any reading of the supply, because the amplifier's highest node is the 450 V reservoir. Simulated with the drawn values the stage settles near 138 V with 0.42 V on its cathode: the 220 Ω leaves the section almost unbiased, so it runs hot and its anode sits low. That is what the drawn parts do; the pair of figures printed beside them is recorded here and left standing."
    },
    {
      "node": "K3B",
      "chart": 3,
      "sim": 0.429,
      "disputed": true,
      "dev_pct": 85.7,
      "tol_pct": 5,
      "gated": false,
      "within": null,
      "note": "",
      "dispute_note": "Same node pair, taken from the cathode side. 3 V across R25's 220 Ω is 13.6 mA — six times the 2.3 mA the 6SL7 data sheet gives for its Class-A point, and 3.2 W dissipated in a plate rated 1 W. R25 is the stage's own unbypassed cathode resistor and nothing else lands on this node: the global feedback resistor R40 returns to the driver's grid (the channel mixing bus), not here, so no second path adds or removes cathode current. There is no reading of this sheet under which 3 V appears here."
    },
    {
      "node": "K3A",
      "chart": 2.2,
      "sim": 1.466,
      "disputed": true,
      "dev_pct": 33.363636363636374,
      "tol_pct": 5,
      "gated": false,
      "within": null,
      "note": "",
      "dispute_note": "Driver V3 unit 1's cathode (pin 6) over R24 1 kΩ, bypassed by 25 µF. 2.2 V is 2.2 mA; 2.2 mA through the drawn 120 kΩ anode load is a 264 V drop, so the 225 V printed at the anode above it would require a 489 V supply. The amplifier's highest node is the 450 V reservoir, and the driver rail sits below it behind R38's 22 kΩ. The stage simulates at 1.47 V with the drawn values, which is 33 % below the printed figure — outside the era's ±20 % — while the anode it feeds lands inside. The contradiction is the sheet's, not the model's, and it is left visible."
    },
    {
      "node": "BP3",
      "chart": null,
      "sim": 383.916,
      "disputed": false,
      "dev_pct": null,
      "tol_pct": 5,
      "gated": false,
      "within": null,
      "note": "informational — the preamp rail both channels share, after R37's 22 kΩ from the screen node (40 µF can). The drawing prints no figure for it",
      "dispute_note": ""
    },
    {
      "node": "BP4",
      "chart": null,
      "sim": 367.111,
      "disputed": false,
      "dev_pct": null,
      "tol_pct": 5,
      "gated": false,
      "within": null,
      "note": "informational — the driver rail, after R38's 22 kΩ from the same screen node (40 µF can). Also unprinted. R37 and R38 leave the screen node together and never rejoin: the sheet's own hop-overs put each on its own horizontal",
      "dispute_note": ""
    },
    {
      "node": "NPP",
      "chart": null,
      "sim": 161.262,
      "disputed": false,
      "dev_pct": null,
      "tol_pct": 5,
      "gated": false,
      "within": null,
      "note": "informational — the paraphase tap itself, the midpoint of R28 470 kΩ and R29 510 kΩ strung across the two driver anodes. It is the whole inverter: it sees the two plates' antiphase swings and feeds the residual to the second grid through C11. No DC path leaves it except through that coupler, so its idle voltage is fixed entirely by the two plates it divides",
      "dispute_note": ""
    }
  ],
  "checks": [
    {
      "id": "dc",
      "title": "DC operating point",
      "status": "Within target",
      "summary": "10 reference nodes are within tolerance. The circuit remains a draft awaiting maintainer review.",
      "details": [
        "3 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": "Open findings",
      "summary": "1 unresolved part.",
      "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: C18, CM2. Heaters and the pilot lamp are checked separately."
      ],
      "tone": "attention"
    },
    {
      "id": "heaters",
      "title": "Heater and filament wiring",
      "status": "Not established",
      "summary": "The drawn supply-leg connections have not been established by this check.",
      "details": [
        "No Ampeg board-layout sheet for the B-15-N was located; this board is derived from the factory schematic, so no factory drawing can establish its heater legs."
      ],
      "tone": "attention"
    },
    {
      "id": "polarity",
      "title": "Capacitor polarity",
      "status": "Checked",
      "summary": "7 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": "b15n-bias-rectifier-2026-10-03",
      "date": "2026-10-03",
      "amps": [
        "b15n"
      ],
      "title": "B15N bias rectifier listed as lettered",
      "description": "The bias rectifier is now listed as the drawings letter it, F-4. Neither cited sheet prints a rectifier type, so the earlier \"selenium\" has been removed.",
      "commit": "138b65854a9368c2cde702d78fb8dce9c2856813",
      "url": "https://github.com/TheAnalogMaker/circuit-codex/commit/138b65854a9368c2cde702d78fb8dce9c2856813"
    }
  ],
  "sourceDirectory": "https://github.com/TheAnalogMaker/circuit-codex/tree/ebddc3fd2cf887dca010bbe60487d7391ea6c052/amps/b15n"
}