Figure 5.9, Vacuum Tube Voltage Regulator Circuit. There is a transformer on the left which has a center tapped secondary. The top goes to the anode of D1 and the bottom goes to the anode of D2. The cathodes of D1 and D2 connect together and to the positive end of C1. The negative end of C1 connects to the center tap. The center tap also connects to the negative output terminal. The positive end of C1 goes to the plate of a triode, V1. The cathode connects to the positive output terminal. The positive output terminal also connects to one end of R5. The other end of R5 goes to the top of a pot R6. The bottom of R6 goes to R7 and the other end of R7 goes to the negative output terminal. The cathode of V1 connects to its grid through R4. The grid of V1 also connects to the plate of V2, a pentode. Grid 1 of V2 connects to the wiper of the pot, R6. The positive end of C1 connects through R1 then R2 to one of the plate pins of V3, a gas filled voltage regulator tube. The junction of R1 and R2 connects to the screen grid of V2. R1 and R2 serve the double purpose of supplying current to the VR tube and providing a voltage source to the screen grid. The cathode and suppressor grid of V2 are connected together outside the tube and connect to the second plate pin of V3. This is part of the protection circuit if power is turned on with V3 removed from its socket. The cathode of V3 connects to the negative output terminal. A resistor R3 connects between the second plate pin to output negative. End verbal description.