Loudspeaker (Jan-Aug 1931)

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change Fig. 4 into Fig. 5. The condenser is “slid” around from the top line to the left vertical line. Then we push the transformer down out of the way, that puts it on the bottom horizontal line. No changes electrically, X just drawing it differently. The battery is also swung through 90 degrees and over. Now we can read all the voltages vertically, making it easier to follow. It can be assumed that no drop in voltage occurs in T or in B. There are 50 volts across R, 40 volts left across RP, and of course the same across C. The current is 2.5 mils. The numerals in Fig. 5 and 6 show the voltages at the points indicated by the arrows. On the negative wave of the signal the current is reduced to 2.25 mils. To make Fig. 5 conform to this new condition we must take out RP and replace it with another RP having somewhat greater resistance. Or if it is variable, increase the resistance slightly. That is more exact. It is FIG.C what happens in the tube. The new values are : R, 45 volts ; RP, 45 volts ; C, 45 volts. To explain the action when the current drops we will assume that we can break the wire between X and C just before the current falls from 2.5 to 2.25 mils. After the change RP will cause a drop of 45 volts, but C will only have 40 volts across it, due to the break between X and C. Fig. 6 ‘-hows this condition. A difference of 5 volts exists across the break. When the circuit is closed again a current must flow. The path of the current is from C through T, through RP, and back to the other side of C. This completes the circuit, and the current will flow until the voltage across C is equal to that across RP, 45 volts. The drop in current increased the charge on the condenser, and in doing so the charging current had to floic through T. Actually, of course, the wire cannot be opened, and the charging current starts to flow as soon as the voltage starts to rise across RP. This happens the instant the current through RP begins to decrease, and is quite gradual. When the current increases on the other half of the signal the reverse action takes place. 2.75 mils flow through RP. The drop in R becomes greater and across RP becomes less. The voltage across RP drops and as this occurs, C is discharging as long as the voltage across RP is falling. As C discharges the current is again going through T, but in the opposite direction than it did on the negative half of the wave. In this manner an alternating current is caused to flow in the transformer. Actual Occurances No. 14796 Manager buzzes fader up one — no response — another buzz and still no effect. Several buzzes more and still no louder. Manager on phone to projection room says: “How come, I buzz you several times and the sound is still soft.” Projectionist ( ?) : “Its loud enough already, the monitor hurts my ears.” /• o r fy s i ’ -t’ e n