several tubes of the same type should be tried when using this circuit. Of course, these sweep tubes can be used in a standard pentode connection as well.

Series Regulator Configurations
  The circuits shown above are of the usual positive-voltage types used in most tube circuits. The relation of this type of regulator to the unregulated power supply driving the regulator is shown in figure 4.10. In this configuration, the unregulated supply can feed many regulators.

pass tube will get a tremendous negative voltage transient. High voltage protection, such as protective gas discharge tubes, should be used.

   If a negative voltage is needed, the circuit of figure 4.3 can be used, with the positive output grounded, as shown in figure 4.11. Since the unregulated supply is floating, it cannot be shared with other regulators.

Series Regulator Examples
A complex system that needs good voltage regulation is a laboratory-grade oscilloscope, and Tektronix made the best oscilloscopes. The following schematics are scanned fragments from various Tektronix scope schematics of the mid 1950s to early 1960s. Tektronix used the design philosophy of providing a single regulated negative supply that served both circuitry and as a reference for the positive supplies. The positive supplies were often "stacked," so that, for example, a 250V regulated supply would be placed on top of a 100V supply to give 350V.

   A variation of the series regulator that is sometimes seen in very high voltage supplies, such as those for CRTs, is shown in figure 4.12. The pass device is put at the negative end of a floating unregulated supply. Only R1 and C1 need to be rated for the high voltage, and the pass device does not need special high-voltage filament transformers or sockets. One caveat, though: if the output is ever shorted to ground, both the comparison device and

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