Figure 9 regulated adjustable voltage power supply using pentode tube or tubes. This supply has 3 transformers. T1 is a plate transformer which now has two secondary windings. One is a 350, zero, 350, volt secondary rated at 200 m eh, and the other is 175 volt winding without a center tap rated at 20 mA. T2 is a filament transformer with a voltage rating the same as the heater of the pass tube or tubes, and a current rating equal to or greater than the total heater current of the pass tube or tubes. T3 is another filament transformer with a 12.6 volt center tapped secondary rated at 6 amps. T2 and T3 may be combined into a single transformer with two secondary windings. The line plug has its ground, round, prong connected to chassis. The neutral prong connects to the bottom ends of the primaries of all three transformers. The hot prong of the plug connects through a 3 amp fuse then the on off switch then to the top ends of the primaries of T2 and T3. The connection at the top ends of the primaries of T2 and T3 connects through the standby switch to the top of the primary of T1. The center tapped secondary of T1 has a 0.005 u f 3 k v capacitor connected across it. One side of this secondary connects to the anode of a diode 1N4007. The other end of the winding connects to the anode of another diode of the same type. The center tap connects to the negative output terminal. The cathodes of the two diodes are connected together and connect to the positive side of a 220 u f 500 V capacitor. The negative end connects to the negative output terminal. The positive end of the 220 u f cap connects to the plate of the pass tube, which is a beam power tube. Note: there could be more than one tube with all of them connected in parallel. The 175 volt secondary has a .005 u f 3 kV capacitor connected across it. The ends of the winding connect to the AC inputs of a bridge rectifier. The negative output of the bridge connects to the positive output of the power supply. The positive terminal of the bridge connects to the positive end of a 22 u f capacitor. The negative end goes to the positive output of the supply. The positive end of the capacitor connects through a 1 k ohm resistor to the positive end of another 22 u f capacitor. The negative end of this capacitor also goes to the positive output terminal. The positive end of the second 22 u f capacitor connects to the screen grid of the pass tube which is indicated as 4 times 6L6GC. A suppressor grid or beam forming element, whichever you prefer, is connected inside the tube to its cathode. The cathode connects to the positive output terminal of the supply. We will leave the pass tube for now. The control grid connection to this tube will be described later. The anode, plate, of a 5651 precision gas discharge voltage regulator tube connects to the negative output terminal of the supply. A third rectifier diode has its cathode connected to one side of the 350 dash 0 dash 350 volt secondary. The anode connects to one end of R3. The other end connects to the negative end of a 47 u f 450 volt capacitor. This point also connects through R4 to the negative end of another 47 u f capacitor. The positive ends of both capacitors connect to the negative output terminal of the supply. The negative end of the second 47 u f capacitor connects through R5 to the cathode of the 5651 regulator tube. The cathode of a small signal pentode, as opposed to the pentode which is the pass tube, connects to the negative output terminal. The control grid of this tube connects to both the wiper and top of a 500 k ohm potentiometer which is the voltage adjust control. The top of the pot connects through R1 to the positive output terminal. The bottom end of the pot connects through R2 to the cathode of the 5651 regulator tube. The screen grid of the small pentode connects through a 390 k ohm 1 watt resistor to the positive end of the 220 u f capacitor. The screen grid also connects to a 100 k ohm 1 watt resistor and a 0.22 u f 630 volt capacitor. The other ends of the resistor and capacitor connect to the negative output terminal of the supply. The suppressor grid connects to the negative output of the supply. The plate of the small pentode connects through a 100 k ohm resistor to the cathode of the pass tube. The plate of the small pentode also connects to the grid of the pass tube. The cathode of the pass tube also connects to one side of its heater. Each side of the heater connects to each side of the secondary of T2. As mentioned earlier, the T1 center tap also connects to an output binding post labeled simply with a minus sign. The cathode of the pass tube goes to another binding post labeled with a plus sign. A third binding post is placed so as to form a triangle with the other two. This one is labeled GND and connects to the chassis. The output is labeled 50 to 400 volts at 200 m eh. The top side of the secondary of T3 connects to a binding post. The center tap connects to another post just below the first. The low side of the secondary connects to a third post just below the second. A fourth post is positioned just below the third and is connected to chassis. Lines and arrows indicate that the voltage between posts 1 and 2 is 6.3 volts AC. The voltage between posts 2 and 3 is also 6.3 volts AC. The voltage between posts 1 and 3 is indicated as 12.6 volts AC. This completes the verbal description.
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