Figure 21. The print figure is of the complete circuit. I feel this is unnecessary for the blind and maybe even helpful. There is only so much I can keep in mind at once and I imagine it is the same for you. Figure 20 is complete in the sense that all tubes, except rectifiers, and associated circuitry have been described. The only gaps are what is inside E1, E2, and E G 2. This description will fill in those gaps. The diagram as drawn has 4 transformers. Note: there are really only two in the actual unit but I didn't have a transformer symbol with that many secondaries and if I had, the diagram would have been harder for me to draw and harder for the sighted to read with many crossings of wires. End of note. The transformers are number T1 through T4 starting at the top left and moving down the left side. T1 has one 6.3 volt secondary at 3.6 amps. T2 has one 140 volt secondary at an estimated 100 mA. T3 has a single secondary 960-0-960, or 1920 center tapped with an estimated current rating of 200 mA. T4 has 4 secondaries; 5 volts at 6 amps, 5 volts at 2 amps 12.6 volts at 600 mA, and 800 CT at 70 mA. There are two other secondaries which I seem to have left out. One would power the heater of the 6W6 pass tube and the power indicator lamp. The other supplies 6.3 volts at 10 amps for the heaters of user circuits. I will not cover these in order from 1 through 4 but logically as they relate to figures 19 and 20 above. The round prong on the power plug is connected to the chassis. The neutral prong goes to the bottom ends of all transformer primaries and the counter clockwise end of the variable transformer. The other flat prong goes through a 4 amp fuse then a switch to the tops of the primaries of T1, T2, T4,and the clockwise end of the variable transformer. Note: The standby switch is at the output not in the primary as in the Heathkit supply. The wiper of the variable transformer connects to the top of the primary of T3. The variable transformer is ganged with the 500 k ohm pot which is the output voltage control. The center tap of the 800 volt winding connects to the minus 300 volt line. The two ends of this winding go to the two plates of V7, 5Y3. The filament of the 5Y3 is powered from and connected to the 5 volt 2 amp winding. Pin 8 of the 5Y3 goes to one side of a 4 u f capacitor, non electrolytic. The other side of this capacitor goes to the center tap. Pin 8 also goes to one side of a 6 henry filter choke. The other end of the choke goes to one end of another 4 u f capacitor. The other end of the cap goes to the center tap. The junction of the second capacitor and choke is the positive terminal of E2. The negative end of E2 is the transformer center tap. There is a 1/8 amp fuse which does not appear in figure 19 and was not mentioned in the description of that figure. Its purpose is to protect the minus 300 volt supply from overloads that a user may connect to the output terminals. When the fuse blows current is cut off to the following parts of the circuit of figure 19 and figure 20. The minus 300 volt adjust pot and the two resistors on either side of it, the cathodes of V9, the cathode of the 5651 voltage reference tube, the cathodes of V13, the output voltage control and the pots and resistors associated with it, and the minus 300 volt output. The fuse is shown in figure 21. The secondary of T2 which is labeled 960 0 960 has its center tap connected through a 1/2 amp fuse to the common line. A 0.0047 u f capacitor is connected across the entire secondary. One end of the secondary connects to both plates of a 5U4 rectifier tube. The other end connects to both plates of another 5U4. The filaments of the two 5U4s are connected in parallel and connect to the 5 volt 6 amp secondary of T4. One side of the filament circuit goes to one side of a 5 henry filter choke. The other side of the choke goes to one side of a 15 u f capacitor. The other side of the cap goes to common. Note: the fuse is between the transformer center tap and common. The junction of the choke and capacitor goes through a 25 k ohm resistor then another 25 k ohm resistor to common. The point where the choke, capacitor, and top resistor come together is the positive end of E1. Common is the negative side of E1. The secondary winding of T2 has each side connected to the two AC inputs of a bridge rectifier. The negative output is the negative of Eg2. The positive output of the bridge connects to one side of a 4 u f capacitor. The other side connects to the negative of Eg2. The positive output of the bridge also goes to one end of a 1 k ohm resistor. The other end of the resistor goes to one end of another 4 u f capacitor. The other end of this cap goes to the negative of Eg2. The junction of the 1 k resistor and the second capacitor is the positive side of Eg2. The secondary of T1 is a 6.3 volt winding. All 4 of the 6L6GC pass tubes have their heaters connected across this winding. On one side of the circuit is a note that says to pin 8 of V6. That's the cathode of one of the 6L6GCs. The 12.6 volt winding on T4 connects across the series connected heaters, pins 4 and 5, of 4 12 eh X 7s, V9, V10, V12, and V13. The center tap of V10 heater, pin 9, is connected to the wiper of a 100 ohm pot. The ends of the pot are connected to the ends of the 12.6 volt secondary. The center tap of V13 heater, pin 9, is connected to the wiper of a 100 ohm pot. The ends of the pot are connected to the ends of the 12.6 volt secondary. This is a rather unorthodox way of balancing the gains of the two triodes within the tube. The center tap, pin 9, of V12 heater connects through a 220 k ohm resistor to minus 300 volts, negative of E2 before the fuse. Pin 9 of V12 also goes through the parallel combination of a 680 k ohm resistor and a 0.01 u f capacitor to common. This completes the verbal description.
Go back.