Figure 25, Schematic of Complete Parametric Equalizer. Input cathode follower and parametric circuit. The input goes to the grid of the cathode follower through a 0.1 u f capacitor. The tube is 1/2 of a 12 A U 7 or a 6 C 4. This grid also connects through a 470 k ohm resistor to ground. The cathode of this triode goes through an 18 k ohm resistor to minus 105 volts. Minus 105 volts also goes through a 0.1 u f capacitor to ground. The cathode goes through a 100 u f electrolytic capacitor to one end of a 100 k ohm resistor. The other end of this resistor is grounded. The junction of the 100 u f and 100 k ohm goes to one end of a 10 k ohm resistor. The other end goes to the inverting input of the tube amplifier. There is another 10 k ohm resistor connected between the inverting input and a point we will call A. The input also goes to the counter clockwise end of the presents control, 5 k ohm. The clockwise end of this control goes to point A. Point A goes through a 560 ohm resistor to the output of the tube amp. The wiper of the presents control goes through a 5.6 n f, 0.0056 u f, capacitor then a 4.7 k ohm resistor to one end of a 500 k ohm pot connected as a rheostat. This is one of a dual ganged pot which is the frequency control. The other end of the first rheostat connects to the second rheostat which is part of the frequency control. The other end of the second rheostat, which is also 500 k ohms, goes through another 4.7 k ohm resistor to ground. The junction of the two rheostats connects through a 3.9 nf, 0.0039 u f capacitor to ground. The junction also connects to the noninverting input of the tube amp.

Now we will describe the internal circuit of the tube amplifier, tube amp.

Tube amplifier.
The inverting input goes to the grid of the left hand triode, one half of a 12AX7. The grid of the right hand triode is the noninverting input. The two cathodes connect together and to one end of a 5.6 k ohm resistor. The other end connects to the drain of a depletion mode M O S F E T, IXCP10M45S. The gate goes through a 1 k ohm resistor to minus 105 volts. The source goes through a 100 ohm resistor, then a 5 k ohm pot connected as a rheostat to minus 105 volts. The plate of the left hand triode goes through a 270 k ohm resistor to a point we will call B plus two. The right hand plate goes through another 270 k ohm resistor to B plus two. B plus two connects through a 22 u f 450 volt capacitor to ground. This is an electrolytic cap and the plus side goes to B plus two. A 47 k ohm resistor connects between B plus two and plus 255 volts. The right hand plate connects directly to the grid of the lower triode in the cascode amplifier, a 12 A V 7. The cathode of this triode goes to ground through the parallel combination of a 27 k ohm resistor and a 100 u f 100 volt capacitor. The plate of the lower triode connects directly to the cathode of the upper triode in the same tube. The grid of the upper triode connects through a 100 k ohm resistor to plus 255 volts and another 100 k ohm resistor to ground. The grid also connects through a 0.1 u f capacitor to ground. The plate of the upper triode goes through a 27 k ohm resistor to plus 255 volts. The plate also goes through the parallel combination of a 330 k ohm resistor and a 5 pf capacitor to the grid of the cathode follower, 1/2 of a 12 A U 7 or a 6 C 4. This grid also connects through a 1.2 n f, 0.0012 u f, capacitor to ground. This grid also goes through a 150 k ohm resistor and then a 100 k ohm pot connected as a rheostat to minus 105 volts. Minus 105 volts also goes through a 0.1 u f capacitor to ground. The cathode of this triode goes through an 18 k ohm resistor to minus 105 volts. The cathode is the output point of the amplifier.
End of verbal description.
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