{
  "schema": 5,
  "revision": "D",
  "status": "ORDER HOLD: axial seating and assembled insulation unresolved; existing PCB retained for review",
  "tube": {
    "model": "SBM-21",
    "overall_nominal_mm": 21,
    "overall_range_mm": [
      20,
      22
    ],
    "can_length_nominal_mm": 16,
    "can_length_range_mm": [
      15.76,
      16
    ],
    "can_diameter_nominal_mm": 6,
    "can_design_range_mm": [
      5.9,
      6.1
    ],
    "terminal_diameter_nominal_mm": 2,
    "terminal_diameter_range_mm": [
      2.01,
      2.15
    ],
    "terminal_projection_reference_mm": 5,
    "source": "https://www.pocketmagic.net/tube-sbm-21-%D1%81%D0%B1%D0%BC-21-miniature-geiger-muller/",
    "tolerance_note": "PocketMagic nominal dimensions control the illustration: 16 x 6 mm body, 5 x 2 mm pin, 21 mm overall. Earlier factory records give 2.01-2.15 mm pin diameter; a nominal 2.03 mm socket is not qualified across that envelope. Measure the supplied tube; do not force insertion.",
    "factory_source": "https://www.gstube.com/scan/2399_1.jpg"
  },
  "polarity": {
    "left": {
      "electrode": "cathode",
      "sign": "-",
      "physical": "closed metal can",
      "pcb_terminal": "MC1",
      "net": "TUBE_LEFT"
    },
    "right": {
      "electrode": "anode",
      "sign": "+",
      "physical": "isolated center terminal",
      "pcb_terminal": "MC2",
      "net": "TUBE_RIGHT"
    },
    "note": "Default assembly: can left, pin right. JP1 selects polarity. MC1/MC2 are physical left/right sites, not fixed electrodes. GM_CATHODE is the pulse pickoff, never GND.",
    "source": "https://theelectronicgoldmine.com/products/G18160"
  },
  "tube_position_mm": [
    33.945,
    4.2
  ],
  "tube_axis_above_pcb_mm": 3.5,
  "axis_height_status": "Provisional 3.5 mm loaded axis; verify on samples. Socket seating offset 0.325 mm.",
  "contacts": {
    "MC1": {
      "manufacturer": "Littelfuse",
      "part_number": "01000058Z",
      "quantity": 1,
      "type": "Low-profile through-hole body spring clip",
      "net": "TUBE_LEFT",
      "position_mm": [
        25.5,
        4.2
      ],
      "body_plan_mm": [
        7.11,
        7.4
      ],
      "body_height_mm": 5.84,
      "pad_offsets_mm": [
        [
          0,
          -2.54
        ],
        [
          0,
          2.54
        ],
        [
          -2.54,
          0
        ],
        [
          2.54,
          0
        ]
      ],
      "pcb_finished_hole_mm": 1.4,
      "pcb_land_diameter_mm": 2.2,
      "footprint": "GC1_RevD:SBM21_Interchangeable",
      "accepted_catalogue_diameters_mm": [
        6.3,
        6.35
      ],
      "purchase_url": "https://www.digikey.com/en/products/detail/littelfuse-inc/01000058Z/2518627",
      "datasheet": "https://www.littelfuse.com/assetdocs/100-58-series-datasheet?assetguid=5b808640-bf54-4935-9350-a02381dfbaf8",
      "fit_status": "6 mm tube can is smaller than the 6.3/6.35 mm fuse specification; verify retention, contact resistance and end-stop seating on actual samples.",
      "dimension_status": "Manufacturer: 7.11 mm axial width, 7.40 mm transverse envelope, 5.84 mm above seating plane; recommended 5.08 mm transverse pitch and 1.32 mm holes. Shared footprint enlarges finished drill to 1.40 mm for the 6049 alternative; sample solderability check required.",
      "illustrative_jaw_profile_mm": [
        [
          0,
          0.2
        ],
        [
          2.4,
          0.2
        ],
        [
          3.1,
          1.0
        ],
        [
          3.2,
          3.4
        ],
        [
          2.65,
          5.1
        ],
        [
          3.5,
          5.65
        ]
      ],
      "fitted_pad_offsets_mm": [
        [
          0,
          -2.54
        ],
        [
          0,
          2.54
        ]
      ],
      "illustrative_stop_center_x_mm": -3.555,
      "illustrative_stop_thickness_mm": 0.3
    },
    "MC2": {
      "manufacturer": "Keystone Electronics",
      "part_number": "6049",
      "quantity": 1,
      "type": "Miniature horizontal spring-contact socket, red nylon",
      "net": "TUBE_RIGHT",
      "position_mm": [
        45.0,
        4.2
      ],
      "body_plan_mm": [
        5.283,
        3.734
      ],
      "body_height_mm": 5.156,
      "pad_offsets_mm": [
        [
          0,
          -2.54
        ],
        [
          0,
          2.54
        ],
        [
          -2.54,
          0
        ],
        [
          2.54,
          0
        ]
      ],
      "pcb_finished_hole_mm": 1.4,
      "pcb_land_diameter_mm": 2.2,
      "footprint": "GC1_RevD:SBM21_Interchangeable",
      "nominal_pin_diameter_mm": 2.03,
      "pin_axis_above_seating_plane_mm": 3.175,
      "provisional_standoff_mm": 0.325,
      "purchase_url": "https://www.digikey.com/en/products/detail/keystone-electronics/6049/316473",
      "datasheet": "https://www.keystone-europe.com/wp-content/uploads/2025/08/pins-plugs-jack-sockets.pdf",
      "fit_status": "2 mm nominal pin is a candidate; factory 2.01-2.15 mm envelope, contact engagement, insertion force and installed HV insulation remain unqualified.",
      "dimension_status": "5.08 mm axial lead pitch; nominal 1.2 mm leads. Both sites provide the same 1.4 mm holes and 2.2 mm lands, including the alternative transverse clip pair. Catalogue miniature-horizontal body width is 0.147 inch (3.734 mm), corrected from the neighboring 0.156-inch socket column.",
      "fitted_pad_offsets_mm": [
        [
          -2.54,
          0
        ],
        [
          2.54,
          0
        ]
      ]
    }
  },
  "assembly": {
    "board_changes": "Both ends use one identical four-hole cross footprint, all four pads numbered 1 on that site net. Populate only the transverse pair for the clip or axial pair for the socket. JP1 underside links select the electrode mapping. H1-H3 retained; H4/H5 removed.",
    "insertion": "Trial-fit the actual tube and contacts without stressing the insulating seal; remove tube before soldering. Select orientation and verify continuity after cooling.",
    "electrical": "Default JP1: 1-3 and 2-4. Reversed JP1: 1-2 and 3-4. Never fit both configurations. No tube flying leads.",
    "fit_check_required": true,
    "production_qualified": false,
    "open_checks": [
      "Resolve axial seating and can-to-anode-pad clearance before ordering; see tube-fit-checks.json",
      "01000058Z retention/contact resistance on a 5.9-6.1 mm can",
      "6049 acceptance of the actual pin (factory envelope 2.01-2.15 mm)",
      "Loaded axis and socket engagement in BOTH assembly orientations",
      "Shared 1.4 mm hole fit, solder fill and tail reach",
      "Three-dimensional can-to-anode-contact and PCB insulation; PCB DRC does not establish assembled insulation",
      "JP1 links and underside enclosure clearance",
      "Enclosure clearance and tube removal path"
    ],
    "order_hold": true,
    "order_hold_reason": "Current nominal model leaves the can off the clip stop, gives only 2.087 mm socket-envelope insertion, and about 1.979 mm can-to-anode-pad clearance against the project 2.8 mm target. Do not order this mounting layout until corrected using measured tube/contact geometry."
  },
  "orientation_selector": {
    "reference": "JP1",
    "footprint": "GC1_RevD:Tube_Polarity_Links",
    "side": "bottom",
    "position_mm": [
      34.8,
      4
    ],
    "pad_size_mm": 1.2,
    "pads": {
      "1": {
        "offset_mm": [
          -2.5,
          -2.5
        ],
        "net": "TUBE_LEFT"
      },
      "2": {
        "offset_mm": [
          2.5,
          -2.5
        ],
        "net": "GM_ANODE"
      },
      "3": {
        "offset_mm": [
          -2.5,
          2.5
        ],
        "net": "GM_CATHODE"
      },
      "4": {
        "offset_mm": [
          2.5,
          2.5
        ],
        "net": "TUBE_RIGHT"
      }
    },
    "default_links": [
      [
        1,
        3
      ],
      [
        2,
        4
      ]
    ],
    "reversed_links": [
      [
        1,
        2
      ],
      [
        3,
        4
      ]
    ],
    "link_material": "Two short 0.3-0.5 mm tinned solid-wire links, 5 mm between pad centers, soldered close to the underside. Use pad numbers; underside viewing mirrors the layout.",
    "instructions": "Power off and discharge. Remove both old links before changing orientation. Swap the body clip and pin socket between MC1/MC2, rotating each 180 degrees. Fit exactly the selected two links. Check can-to-GM_CATHODE and pin-to-GM_ANODE continuity, and no short between them before inserting the tube or applying power."
  }
}