| Diagram of the dark box with the HPD module installed. V<sub>HV</sub> = -12 kV, V<sub>b</sub> = 60 V.
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| Diagram of the dark box with the HPD module installed. V<sub>HV</sub> = -12 kV, V<sub>b</sub> = 60 V. ±5 V provide the supply rails for the amplifier built into the HPD module.