3. Select the next largest standard value of resistance for the series resistor (6800 ohms in this case).
With a properly adjusted output resistance combination, the positive voltage is continuously variable from about 125 volts to 375 volts. The current capacity of the positive supply is limited by li e current rating of transformer at the higher voltages and by the maximum permissable plate dissipation of the 6AQ5A at the lower voltages. For a unit with 1.00 milliamp power transformer, operation should he maintained within the iCsafe operating r&nge" diagrammed in Fig. 3, Regulation is not as good a:>ove 325 volts as it is on lower voltages, but it is still stiff enough for the majority oi breadboard circuitry and bias applications.
Thus far very little has been said about the variable negative voltage. This circuit is a straightforward shunt regulator using zener diodes in place of the familiar gas regulator tube. With the diodes shown in (he schematic, this voltage is available from zero to about - 180 volts. The current capacity of the negative supply is determined by the power rating of the regulatory diodes; for 10 watt devices, 30 milliamperes is available on a continuous basis. With the addition of a suitable heat sink, this could be just about tripled, but a much larger chassis would be required.
Most of the commercially available stud-mounted regulator diodes are designed for regulating positive voltages and as such, the chassis mounting stud is located at tlife cath
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