Figure 14 regulated adjustable voltage power supply with improved range using an op amp in place of the amplifier tube. This supply has 3 transformers. T1 is a plate transformer with a 350, zero, 350, volt secondary rated at 200 m eh. 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 secondary of T1 has a 0.005 u f 3 k v capacitor connected across it. One side of the 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 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 center tap of the secondary. The positive end of the 220 u f cap connects to the plate of the pass tube, shown as a triode. Note: A pentode could also be used. Note: there could be more than one tube with all of them connected in parallel. We will leave the pass tube for now. Other connections to this tube will be described later. The center tap of the transformer secondary connects to the anode, plate, of a 5651 precision gas discharge voltage regulator tube. That's no mistake, I typed anode and I meant anode. 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. The positive end connects to the center tap. The negative end of the capacitor also connects through a resistor R4 to the cathode of the 5651 regulator tube. Note: for a discussion of the values of R3 and R4, see text. This circuit contains an op amp symbol. There is no op amp made today that would work in this circuit. This is a theoretical circuit to illustrate a principle. The negative power supply rail of the op amp connects to the center tap. The inverting input of the op amp 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 noninverting input connects to the anode of the regulator tube, which is also the center tap of the transformer high voltage winding. See text. The positive power supply rail of the op amp connects to the positive side of the 220 u f 500 V capacitor. The output of the op amp 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. 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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