Figure 21, DC Coupled Amplifier, Closer to True Op Amp. The input goes to the grid of the left hand triode, one half of a 12AX7. This is the inverting input. It connects to ground through a 1 meg ohm resistor. The grid of the right hand triode is the noninverting input. It also goes to ground through a 1 meg ohm resistor. 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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