Figure 7.1. Overview. The signal input goes to the input of the input buffer amplifier which is a tube circuit. The output of the buffer goes to the input of the response control circuit which is made up entirely of passive elements. The center of the response control circuit goes to the input of the feedback amplifier which is another tube circuit. The output of the feedback amplifier goes to the output side of the response control circuit. The output of the response control circuit is also the signal output.

The Input buffer. The input terminal on the left connects to a 0.1 u f capacitor. The other end goes to the grid, pin 2, of a 12AU7. The plate, pin 1, connects to plus 250 volts. The cathode, pin 3, goes to a 3.9 k ohm resistor. The other end goes to a 33 k ohm resistor. The other end of that one goes to ground. The junction of the 3.9 k and 33k connects to one end of a 470 k ohm. The other end goes to the grid, pin 2, of the same tube. The other triode in this 12AU7 is used in the other channel of the amplifier or preamplifier. The cathode, pin 3, goes through a 2.2 uF 200 volt capacitor to the input of the response control circuit.

The response control circuit. The input side of this circuit is at the junction where two 10 k ohm resistors and a 1000 pf capacitor all connect together. This point goes through a 470 k ohm resistor to ground. The other end of the capacitor connects to the clockwise end of the treble pot, 100 k ohm. The other end of this pot connects to one end of another 1000 pf cap. The other end goes to the output side of the response control circuit. The output side of the response control circuit goes through a 470 k ohm resistor to ground. The connections to the ends of each pot will be described and then the wiper connections will be explained. One of the 10 k ohm resistors from the input side goes to the clockwise end of the midrange pot, 100 k ohm. The other end of this pot goes through another 10 k ohm resistor to the output side of the RCC. There is a 1600 pf capacitor connected from one end of the midrange pot to the other. The other 10 k ohm resistor that connects to the input side of the RCC goes to the clockwise end of the bass pot, 100 k ohm. The other end goes to another 10 k ohm resistor to the output side of the RCC. There is a 0.056 u f cap connected from one end to the other of the bass pot. The wiper of the treble pot goes through a 47 k ohm resistor to the input of the feedback amplifier. The wiper of the midrange pot goes through a 3300 pf capacitor then a 100 k ohm resistor to the input of the feedback amplifier. The wiper of the bass pot goes through a 100 k ohm resistor to the input of the feedback amplifier.

The feedback amplifier. The input of the feedback amplifier is at one end of a 0.1 u f 200 volt capacitor. The other end of this capacitor goes to the grid, pin 7 of a 12AX7. Pin 7 also goes to ground through a 1 meg ohm resistor. The cathode, pin 8, goes to ground through the parallel combination of a 3.9 k ohm res and a 100 u f cap. The plate, pin 6, goes through a 750 k ohm resistor to plus 250 volts. The other triode in the 12AX7 is used in the other channel of the amplifier or preamplifier. The plate, pin 6, of the 12AX7 goes to the grid, pin 7, of a different 12AU7. The plate, pin 6, of the 12AU7, goes directly to plus 250 volts. The cathode, pin 8, goes through a 33 k ohm to ground. The other half of this 12AU7 is used in the other channel. Pin 8 goes through a 0.1 uF 630 volt capacitor to the output side of the response control circuit. The output point of the RCC also goes through a 0.22 u f 200 volt capacitor to the signal output. The signal output also goes to ground through a 470 k ohm resistor. End verbal description.
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