Figure 5.10, Improved Vacuum Tube Voltage Regulator Circuit. On the left an AC power plug is shown with the lower, wide, prong connected to the bottom of the primary of T2 and also the bottom of the primary of T1. The top prong goes through an S P S T switch which is labeled power then a fuse to the top of the primary of T2. The junction of the switch and fuse connects to another S P S T switch which is labeled high voltage. The other end of the switch goes through another fuse to the top of the primary of T1. T1 has two secondaries and they are both center tapped. The top of secondary 2 connects to the top AC terminal of a bridge rectifier. The bottom of the secondary connects to the bottom AC input of the bridge. The center tap connects to, among other things, the negative output terminal of the power supply. The positive output of the bridge connects to the positive end of a capacitor, C1. The negative end connects to the center tap. The positive end of C1 connects to the plate of V1. This may be two or four tubes in parallel. The cathode of V1 connects to one side of its heater and to the positive output terminal. Grid 3 of V1 is connected to the cathode inside the tube. The positive terminal also connects to one end of R7. The other end of R7 connects to the top of a pot, r8. The bottom of R8 connects through R9 to the minus 300 volt point. This will be explained all in good time. Returning to C1, its positive end connects to one end of R4. The other end goes to one end of R5. The other end of R5 goes to the negative output terminal. The junction of R4 and R5 connects to the screen grid of V2. The plate of V2 connects to grid 1 of V1. R6 is connected between the cathode and grid of V1. Grid 1 of V2 is connected to the wiper of the pot, R8. Grid 3 and the cathode of V2 are connected together outside the tube and also connect to one side of its heater. These also connect to the minus 150 volt point. The negative output of the bridge rectifier, that is connected to secondary 2, is connected to one end of a resistor R1. The other end of R1 connects to the negative side of C2. The positive of C2 goes to the center tap. The junction of R1 and C2 goes to one end of R2. The other end of R2 connects to the negative side of C3. The positive of C3 connects to the center tap. The junction of R2 and C3 goes to R3. The other end of R3 goes to the first cathode pin of V4, zero D 3, 150 volt voltage regulator tube. The second cathode pin is not used. The third cathode pin goes to the minus 300 volt point. The first plate pin of V4 connects to a cathode pin of V3, another zero D 3. The other two cathode pins are not used. The second plate pin of V4 goes to the minus 150 volt point. One of the plate pins of V3 connects to the negative output terminal. The other plate pin is not used. Secondary winding 1 on T1 has each side connected to the anode of a diode. The cathodes of the two diodes are connected together and go to the positive end of C4. The negative of C4 goes to the center tap of winding 1. The positive of C4 goes to one end of R10. The other end of R10 goes to the positive end of C5. The negative end of C5 goes to the center tap. The junction of C5 and R10 goes to one end of R11. The other end of R11 goes to the positive end of C6. The negative end of C6 is connected to the center tap. The junction of R11 and C6 goes to the screen grid of V1. The center tap connects to the cathode of V1. T2 has three windings all of them 6.3 volts. Winding 1 connects to two output terminals labeled 6.3 VAC output. Winding 2 goes to the heater of V2 the error amplifier. The cathode of this tube is at minus 150 volts with respect to the circuit common which exceeds the maximum heater to cathode rating of 90 volts. One side of the heater is connected to the cathode so they will always be at the same potential. Winding 3 connects to the heater or heaters of the pass tube or tubes, V1. One side of the heater is connected to the cathode of one of the pass tubes. End verbal description.