Model DR81


  • Secondary: 8.25” x 34” winding length, 24AWG wire (same as 81G)
  • Topload: 34” x 8” corrugated drain pipe covered with foil tape (same as 81G)
  • Primary: 15T of 3/8” soft copper tubing, 3/8” edge-edge spacing (same as 81G)
  • Primary Capacitor: 5s16p CDE942C20P15K MMC, 0.48uF @10KVDC, 216A RMS, 6912A peak
  • Frequency: Secondary system is 70kHz, primary is detuned to roughly 65kHz (turn 4)
  • Bridge
    • Layout: H-bridge with voltage doubler for 680VDC with 240VAC input
    • IGBT: 2x Mitsubishi CM300DY-24H
    • Bus capacitor: 5500uF @ 900VDC. 2x CDE 520C 11000uF, 450VDC inverter-grade electrolytic in series. 15kOhm / 10W bleeder/balance resistors
    • Bus: Laminated, 1/16” aluminum, 1/16” G10/FR4 insulating layer
    • Rectifier: Semikron semipak SKKD81/16
    • Snubber: 2x Aerovox RBPS direct-mount, 2uF 1000VDC each
  • Driver: UD2.7C
  • Feedback/OCD: 50:20:1 current transformers, Fair-rite Type 77 (5977003801 and 5977006401)
  • Interrupter: Dual Channel MIDI Interrupter
  • OCD: Currently set to 800A. Could probably handle 1000A+
  • Arc length: ~7ft with ~200VAC input running ~45uS on-time while playing music.


In early 2018, I was bit by the DRSSTC bug when it became apparent just how much heavy iron I had accumulated in my quest to bring my 15kVA Pole Pig powered SGTC online.

I already had a large heatsink salvaged from a 7kVA UPS system. I figured I could reconfigure my existing CDE 942C MMC to get one good for 0.48uF, 10kVDC 216A RMS. I simply needed a driver, bus caps, interrupter, IGBTs, laminated bus, gate drive transformer, and a few other odds and ends to construct the bridge.

This coil is based around a full bridge of CM300DY-24H modules, a voltage doubler arrangement for 5500uF @900VDC, Gao Guangyan’s UD 2.7 driver, and the same 8” secondary and 3/8” primary from the 8” SGTC”.

This coil saw first-light Sept 17 2019, and the first full-power run was conducted Sept 21 2019 without any issues whatsoever.





The driver is Loneocean’s UD 2.7C, with the HFBR series ST fiber module installed.


Results of low-power testing were promising. Phase lead was adjusted for minimal ringing on the DC bus.

  • Yellow: Gate voltage
  • Cyan: Bus voltage
  • Magenta: Primary current


Low power

High power