Figure 8.8 A Typical Ratio Detector. On the left side of the diagram is a pentode tube. This is the last F M, I F amplifier. Only the plate is shown connected. It is connected to the top of the primary of the discriminator transformer. The primary is tuned by a variable capacitor. The secondary is center tapped and tuned by another variable capacitor. The top of the secondary goes to the plate of V2 eh, a 6AL5. The bottom of the secondary goes to the cathode of V2B. The V2 eh cathode goes through two 330 p f capacitors in series to the plate of V2B. We will return to the junction point of these two capacitors later. The cathode of V2eh goes through a 2.2 k ohm resistor then a 10 k ohm resistor to ground. The plate of V2B goes through a 10 k ohm resistor to ground. There is a 5 u f capacitor connected from the junction of the 2.2 k and 10 k to the junction of the other 10 k ohm resistor and the plate of V2B. One end of the tertiary winding connects to the center tap of the secondary. The tertiary winding is not tuned. The other end of this winding connects through a 68 ohm resistor then a 330 p f capacitor to ground. The junction of the 68 ohm and 330 p f goes to the junction of the two 330 p f capacitors we left hanging earlier. The junction of these components is an output point labeled m p x which stands for multiplex. The m p x output goes through a 75 k ohm resistor then a 0.001 u f capacitor to ground. The junction of the 75 k and 0.001 u f goes to an output labeled monaural audio. The point where the plate of V2B, one of the 330 p f capacitors, one of the 10 k ohm resistors, and the 5 u f capacitor all connect together goes to one end of a 470 k ohm resistor. The other end of this resistor goes to an output point labeled AGC. End verbal description.
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