Schematic diagram of the power supply and amplifier. Part 1 the basic unregulated power supplies. There are two power transformers in this unit. T1 has a 600 volt center tapped winding rated at 110 mA, a 5 volt 2 amp, and a 6.3 volt 5amp winding. T2 has a 125 volt winding at 15 mA, and a 6.3 volt estimated at 2 Amps. The 5 volt winding on T1 is not used. The wide prong (neutral) of a polarized line plug goes to one side of the primary of T1 and also to one side of the T2 primary. The narrow prong (hot) goes to the on/off switch part of the volume control. The other end of the switch goes to one end of a 1 amp slow blow fuse. The other side goes to the unused side of the T1 primary. The on/off switch also goes to a 0.3 amp slow blow fuse and the other side goes to the primary of T2. The 6.3 volt winding of T1 is center tapped and the center tap is grounded. The two ends of this winding go to the heater connections of the 12AX7, 6V6, and 6AU6. The 6.3 volt leads also go to two green binding posts labeled 6.3 VAC output. The 5 volt winding is not used. The center tap of the 600 volt winding is grounded and the two ends go to the AC inputs of a standard bridge rectifier. The positive output of the bridge goes through a 22 ohm 1/4 watt resistor to the positive of a 40 microfarad 450 volt cap. This point goes through a 4 henry 150 mA filter choke to the positive of another 40 mike 450 V cap. The negative end of both caps is grounded. The positive of the second cap is labeled plus 400 volts. The negative output of the bridge rectifier goes through a 10 k ohm 2 watt resistor to the negative of a 16 mike 450 v cap. This point goes through a 5.6 k ohm 1 watt resistor to the negative of a 13 mike 150 v cap. The positive of both caps is grounded. The negative of this last cap is labeled minus 140 VDC. The point labeled minus 140 v goes through an 18 k ohm 1 watt resistor to the top of a 10 k ohm pot. The top of the pot goes through a 47 microfarad 50 v cap to ground. The bottom of the pot is grounded and the wiper connects to a binding post labeled 0 to minus 50 VDC grid bias. The 125 v secondary of T2 has no center tap. Each end goes to the AC inputs of a standard bridge rectifier. The negative output of the bridge connects to the negative terminal of a triple can cap. It is a 50, 50, 150 mike, 150 v. The positive output of the bridge goes through a 150 ohm resistor to the positive of a 50 mike cap in the afore mentioned can. From there another 150 ohm resistor goes to the other 50 mike cap and from there another 150 ohm resistor goes to the 150 mike cap. A 27 k ohm 2 watt resistor connects from the positive of the 150 mike cap to its negative. The positive is labeled screen supply positive and the negative is labeled screen supply negative. Neither side of this last supply is grounded nor is any part of it. Part 2 the regulator. The point labeled minus 140 v goes through a 22 k ohm and a 20 k ohm resistor in parallel to pin 2, cathode, of the 5651 voltage regulator tube. Pin 5, anode, of the 5651 is grounded. The minus 82 volts regulated is taken from pin 7 which is another cathode connection. If the tube is removed from its socket this voltage disappears. A 6AU6 has its cathode, pin 7, grounded. The heater, pins 3 and 4 connect to the 6.3 volt heater supply. The suppressor grid, pin 2 is also grounded. A zener diode, 1N752A 5.6 volt, has its anode connected to the grid, pin 1, of the 6AU6. The cathode of the zener is grounded. A 24 k ohm resistor connects from pin 7 of the 5651 to one end of a 10 k ohm pot connected as a rheostat. The other end of this rheostat connects to another 10 k ohm pot also connected as a rheostat. The first pot is labeled 300 v cal and the second is labeled 30 v cal. The junction of the two pots goes to the grid, pin 1, of the 6AU6. The as yet unconnected terminal of the second 10 k ohm pot connects to one end of a 100 k ohm pot also connected as a rheostat. This is the output voltage adjust. The other end of this pot connects through an 8.2 k ohm resistor to the positive regulated output. A 0.1 mike 600 v cap connects from this point to the grid, pin 1, of the 6AU6. An 82 k ohm 1 watt resistor connects from plus 400 v to the screen, pin 6, of the 6AU6. A 27 k ohm goes from the screen to ground. This combination serves as a bleeder resistor for the 400 v power supply. A 2 mike 200 v cap goes from the screen grid, pin 6, of the 6AU6 to ground. The positive side is to pin 6. The plate, pin 5, of the 6AU6 goes through a 270 pf 500 v cap to ground. The plate also goes to pin 1, grid, of both 6AQ5s. This common point of the 6AU6 plate and 6AQ5 grids also goes through a 100 k ohm resistor then through another 100 k ohm resistor to the screen supply positive. The junction of the two 100 k ohm resistors goes through a 2 mike 200 v cap to the screen supply negative. The screen supply positive also connects through a 100 ohm resistor to pin 6, screen grid, of one of the 6AQ5s. The screen supply positive also goes through another 100 ohm resistor to pin 6 of the other 6AQ5. The screen supply negative connects to the regulated output which also connects to a binding post output. Each 6AQ5 cathode connects through its own 82 ohm resistor to the regulated output. The screen grids of the 6AQ5s are always 150 volts higher than the cathodes no matter what the output voltage may be set to. This allows the tubes to operate as pentodes rather than triodes as would be the case if the screen grids were tied to the plates. Each plate of the 6AQ5s connects through its own 100 ohm resistor to plus 400 volts. pin 4, heater, of one 6AQ5 is connected to pin 4 of the other 6AQ5. The two pin 3s are also connected together. The two parallel connected heaters are connected to the 6.3 volt winding on T2. The two pin 4s are connected to the regulated output. This places the heaters at the same positive potential as the cathodes so as not to strain the heater to cathode voltage rating. Part 3 the audio amplifier. Pins 4 and 5, heaters, of the 12AX7 are tied together and connect to one side of the 6.3 v winding on T1. Pin 9 goes to the other side of the winding. The audio input is by means of a binding post or an RCA phono jack. This point goes through a 0.01 mike 600 v cap to the top of the volume control pot, a 500 k ohm audio taper with an on/off switch on the back. The bottom of the pot is grounded and the wiper goes through a 0.1 mike cap to the grid, pin 7, of half of the 12AX7. Pin 7 also connects through a 470 k ohm resistor to ground. The cathode, pin 8, connects through a 1.8 k ohm resistor to ground. The plate, pin 6, connects through a 100 k ohm resistor to the positive side of a 4 mike 450 v cap. We'll get back to this cap in a while. Pin 6 also connects through a 0.01 mike 600 v cap to the grid, pin 2 of the other section of the 12AX7. Pin 2 connects through the parallel combination of a 470 k ohm resistor and a 68 pf cap to ground. The cathode, pin 3 connects through a 4.7 k ohm resistor to ground. The plate, pin 1, connects through a 470 k ohm resistor to the positive of the 4 mike 450 v cap mentioned earlier. Pin 1 also connects through a 0.01 mike 600 v cap to the grid, pin 5 of the 6V6. Pin 5 also goes through a 470 k ohm resistor to ground. The heater, pins 2 and 7, connect to the 6.3 volt winding. The cathode, pin 8, goes through a 390 ohm resistor to ground. The red primary lead of the output transformer goes to the plus 400 volt supply. The blue primary lead goes to the plate, pin 3 of the 6V6. A 0.001 mike 400 v cap connects to the red lead. the other end of the cap goes through a 22 k ohm 1 watt resistor to the blue lead. From the red lead, plus 400 v point, a 47 k ohm resistor connects to the screen grid, pin 4, of the 6V6. The positive side of a 4 mike 450 v cap goes from pin 4 to ground. Another 47 k ohm resistor goes from pin 4 to the other 4 mike 450 v cap from a while ago. The negative sides of both 4 mike 450 v caps are grounded. The speaker connects to the 4 ohm tap on the secondary of the output transformer and the other side of the speaker and the secondary common are grounded. The 16 ohm tap on the secondary goes through the parallel combination of a 680 ohm resistor and a 0.001 mike cap to one end of a 100 ohm resistor. The other end of the 100 ohm resistor is grounded. The ungrounded end of the 100 ohm resistor goes to the negative side of a 10 mike cap. The positive end of this cap goes to pin 3, cathode, of the 12AX7. This provides negative feedback. End of verbal description.
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