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(Continued from Page 21) side of the condenser, around the circuit to the other side. We say the condenser becomes charged. After the condenser is charged no more current will flow in either direction as long as the voltage across it demains unchanged. If the voltage across the condenser is changed to 41 volts a current flows for an instant, and it will be in the same direction as the current flowed when the amplifier was turned on. If the voltage be lowered to 40 again the flow of current will be in the reverse direction. If the voltage is lowered still further another similar current flows for an instant. Each time the voltage across the condenser is varied a current flows, the direction depending upon whether the voltage is increased or decreased. The important point is that the current flow is through the primary of the transformer. Every time the condenser is partially charged or discharged a current flows through the primary. This is the signal..
A signal is now put into the tube. This reduces the plate current to 2.25 mils on the negative wave. 2.25 mils will not cause so great a drop in the coupling resistance as 2.5 mils did. It will produce a drop of 45 volts (.00225 times 20,000). This leaves a voltage of 45 across the plate and filament of the tube, which is an increase of 5 volts. The increased voltage is also applied to the condenser, which becomes charged a little more. The charging current going from one side of the condenser, through the transformer primary, then through the C battery, over to the filament of the first tube, to the plate, and finally back to the other side of the condenser.
We can make this more clear by redrawing Fig. 2 a couple of times, leaving out everything that does not enter into the business of charging and discharging the condenser.
Fig. 3 shows the first step. The tube is represented by the resistance RP inside the circle. This is because
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the path from plate to filament in the tube looks like a resistance to the rest of the circuit, and acts like one; a varying resistance. The filament in Fig. 2 is hooked to negative B, so we draw the line from the bottom of RP to point Y at the negative end of B. The top of RP goes to X, to which is also connected the coupling resistance R and the isolating condenser. R and the battery B are in series as they are in Fig. 2. From the condenser we go to the transformer T, but we only show half of the transformer, the primary. The secondary does not enter into this. We also leave out the C battery, so the wire goes from T to Y. This looks different, but just imagine that the circle is a tube, which it represents, then study Fig. 2 and Fig. 3 for a second and you will see that they are quite the same.
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Next is Fig. 4. This is exactly the same hook-up as Fig. 3. The portion to the right of X and Y in Fig. 3 is drawn in with dotted lines in Fig. 4, and to the left of the points X and Y. In Fig. 3 the condenser is connected to X. In Fig. 4 it is connected to the other end of the same wire. It is still connected at a point between R and RP. In Fig. 4, Y has been slid along the wire so it now is under RP It was under B in Fig. 3. The transformer T is again connected to Y.
By another twist of the wrist we