Figure 2.6 Signal Tracer. Since you are building this instrument you can decide what kind of input connector to use. I used a BNC connector. The outer shell of the connector is grounded to the chassis. The center conductor goes to one end of a 0.01 u f 630 volt capacitor. The other end of the cap goes to the top of a 500 k ohm audio taper pot. The bottom is grounded. The wiper of the pot goes to one end of another 0.01 u f 630 volt capacitor. The other end goes to the grid, pin 7 of a 12AX7. The grid also goes to ground through a 470 k ohm resistor. The cathode, pin 8, goes to ground through a 1.8 k ohm resistor. The plate, pin 6, goes through a 100 k ohm resistor to a point we will call B plus three. Pin 6 also goes through a 0.01 u f capacitor to the other grid, pin 2, of the 12AX7. Pin 2 also goes to ground through a 470 k ohm resistor. The cathode, pin 3, goes to ground through a 1.8 k ohm resistor. The plate, pin 1, goes through a 100 k ohm resistor to B plus three. The plate also goes through a 0.01 u f capacitor to the grid, pin 5, of a 6V6 GT. Pin 5 also goes to ground through a 470 k ohm resistor. Pin 5 also goes to ground through a 470 p f capacitor. The cathode, pin 8 of the 6V6 goes to ground through a 150 ohm 1 watt resistor. The screen grid, pin 4, goes directly to B plus 2. The plate, pin 3 goes to the blue lead of the primary of the output transformer. The red lead of the primary goes to B plus 1. The blue lead goes through a 22 k ohm 1 watt resistor then a 0.001 u f capacitor to the red lead. The two primary leads, usually enameled copper, go to the two terminals of the speaker, each wire to one of the speaker terminal. The output transformer is labeled 5 k ohm primary to voice coil and has the note see text. The power transformer is a Hammond 261G6, 250 V @ 140 mA. The primary is connected to the power line as follows. A 3 conductor line cord has its green wire connected to chassis ground. The white wire connects to the bottom end of the primary. The black wire connects through an S P S T switch then a 1/2 amp fuse to the top of the primary. The heater winding is connected to the heaters of the tubes as follows. Top of the winding to pin 9 of the 12AX7, and pin 2 of the 6V6. Bottom of the winding to pins 4 and 5 of the 12AX7 and pin 7 of the 6V6. There is a 0.003 u f 3 kV capacitor connected across the high voltage secondary. Each end of this winding goes to the anode of a diode, 1N4007. The cathodes of the two diodes are tied together and go to one end of a 100 ohm 1 watt resistor. The other end of the 100 ohm goes to the positive end of a 47 u f 250 volt capacitor. The negative end is grounded. The junction of the resistor and capacitor is B plus one. A 1.5 k ohm 1 watt resistor goes from B plus 1 to B plus two. Another 47 u f capacitor goes from B plus two to ground. A 10 k ohm resistor connects from B plus two to B plus three. There is a 10 u f 250 V capacitor connected from B plus 3 to ground. The negative end is grounded. B plus three goes through a 100 k ohm 1/2 resistor then a 10 k ohm resistor to ground. There is a 10 u f 25 V capacitor connected in parallel with the 10 k ohm resistor. The negative end is grounded. The junction of the 100 k and 10 k connects to the junction of two 150 ohm resistors. The other end of one of the 150 ohm goes to the top of the heater winding. The other end of the other 150 ohm goes to the bottom of the heater winding. This completes the verbal description.
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