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High voltage: CRTs operate at very high voltages. These voltages can persist long (several days) after the device containing the CRT has been switched off and unplugged. Residual charges of hundreds of volts can also remain in large capacitors in the power supply circuits of the device containing the CRT; these charges may persist for weeks. (Modern circuits contain bleeder resistors to ensure the high-voltage supply is discharged to safe levels within a couple of minutes at most.)
Those working inside CRT-containing equipment should know how and be able to safely discharge these hazards. In particular, the large rubber connector which looks like a suction cup is responsible for supplying accelerating voltage to the bell of the CRT. Under the suction cup is the ultor which couples the accelerating voltage to the inside of the tube. Inside the glass bell is a coating of metallic paint, while the outside of the bell is coated with a conductive graphite coating called Aquadag; between the ultor's connection to the flyback transformer and the Aquadag, there is therefore a capacitance capable of maintaining the full accelerating voltage for weeks. While this accelerating voltage is high (typically from 7kV to 50kV depending on screen size, monochrome or color, direct view or projection), both the capacitance and flyback current are small (on the order of picofarads and nanoamperes respectively), so shocks from the accelerating voltage are typically embarrassing and painful but usually harmless. On the other hand, the voltages and available currents used in the deflection and power supply circuits can result in instantaneous death.