Figure 20, simplified schematic of 0 to 500 volt regulator circuit contained in the HP 712B rack mount regulated power supply. This power supply has two outputs. One is fixed minus 300 volts and the other is zero to 500 volts adjustable by a large knob on the front panel. The current rating of the minus 300 volt output is 50 mA while the 0 to 500 volt output has a rating of 200 mA. In this simplified diagram the rectifier filter circuits are represented by batteries. Some of the voltages given depend on the setting of the output voltage control. Values are given with this control set to maximum, 500 volts. The left hand grid of V13, 12 eh X 7, goes through a 220 ohm resistor then a 33 k ohm resistor to the anode of the 5651 reference tube, V11. A 0.1 u f capacitor connects from the junction of the two resistors to common. The anode of the reference tube goes through an 80 k ohm resistor to common. The two cathodes of V13 are tied together and go through a 120 k ohm resistor to minus 300 volts. The voltage at the cathodes is indicated as minus 212 volts. Each plate of V13 goes through its own 330 k ohm resistor to common. The voltage at each plate is given as minus 55 volts. The left hand plate of V13 connects to the left hand grid of V12, 12 eh X 7. The right hand plate of V13 connects to the right hand grid of V12. The two cathodes of V12 are tied together and go through a 200 k ohm resistor to minus 300 volts. The right hand plate of V12 goes through a 3 meg ohm resistor to the left hand grid of V12. The left hand plate of V12 goes through a 1.5 meg ohm resistor then another 1.5 meg ohm resistor to the right hand grid of V12. A 150 p f capacitor connects from the junction of the two 1.5 meg ohm resistors to the right hand plate of V12. The left hand plate of V12 goes through a 1.5 k ohm resistor to the grid of the pass tube which is actually 4 6L6GCs in parallel. The left hand plate of V12 also goes through a 390 k ohm resistor to the positive terminal of E g 2 which has a voltage between its terminals of 185 volts. The negative of E g 2 connects to the cathode of the pass tube. The right hand plate of V12 also goes to the cathode of the pass tube. The screen grid of the pass tube goes to the positive of E g 2. The plate of the pass tube goes to the positive of E1. The negative goes to common. E1 is indicated as being a variable supply. More about this in a moment. The right hand grid of V13 goes to the wiper of a 50 k ohm pot which is the 500 volt adjust, a screwdriver adjustment. The bottom end of the pot is connected to the wiper making it a rheostat. The bottom end also goes through a 37 k ohm resistor to minus 300 volts. The upper end of this pot goes to one end of an 83 k ohm resistor. The other end of this resistor connects to the lower end of a 500 k ohm pot which is a user control, the output voltage adjust. A dashed line indicates that the pot is ganged with E1. As the output voltage is decreased the voltage supplied to the plate of the pass tube is decreased to keep its plate to cathode voltage and therefor its plate dissipation within limits. The wiper of the output voltage control is connected to the upper end to make it a rheostat. The upper end connects to another 50 k ohm pot which is also connected as a rheostat. This pot is labeled zero volt adjust and is a screwdriver pot. We will come back to the upper end of this rheostat later. The cathode of the pass tube connects to one end of a 0.01 u f capacitor. The other end of this capacitor connects to the junction of the 500 volt adjust and the 83 k ohm resistor. The cathode of the pass tube also connects to one end of a 0.6 ohm resistor. The other end connects to the positive side of the load current meter, 0 to 200 mA. The negative side of the meter connects to one end of a 1 k ohm resistor. The other end of the resistor connects to the top of the zero volt adjust rheostat which we left hanging earlier. A 0.4 u f capacitor connects to the junction of the 1 k ohm resistor and the zero volt adjust rheostat. The other end of this capacitor connects to the junction of the 500 volt adjust rheostat and the 83 k ohm resistor. That's no mistake. The diagram clearly says 83 k ohms. The negative terminal of the current meter also connects to one side of a single pole single throw switch, high voltage on / off. The other side of the switch connects to the high voltage, 0 to 500 volts, output jack on the front panel. This completes the description of the diagram.
Go back