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498 RICHARDSON'S BLUEBOOK OF PROJECTION
it. The circles represent the glass envelopes of rectifying tubes. The "V" 's are the filaments, which emit negatrons when heated.
It will simplify matters to forget all the rest of the charger for the moment, and see how those filaments are supplied with heating current.
At the lower right of the drawing is a terminal block to which an a. c. power line is wired through some external switch that will serve to turn the charger on and off. From the a. c. terminals of this block wires run around the bottom of the drawing to the primary winding of a transformer, which is equipped with three taps, arranged to accommodate voltages from 105 to 125, according to voltage of the power supply line.
A. c. from the line flows through this primary and completes its circuit back to its source and in so doing generates alternating voltages in the three secondaries of the transformer, as explained on Page 461. The top secondary, marked "Fil. No. 1," and the bottom secondary, marked "Fil. No. 2," are wired directly to the filaments of the two tubes, No. 1 and No. 2, and the current generated in those secondaries heats the filaments.
Now let us assume that those filaments are heated, and emitting negatrons, and forget about their secondaries, which serve no other purpose than to heat them. The rectifying action proper is concerned only with the middle secondary of the transformer, and with the horizontal lines (plates) drawn above the filaments of the two tubes.
Rectifying Tube and Its Circuits
(15) The type of rectifying tube shown in Figure 114 contains within its glass, but completely insulated from the filament, a plate of metal or carbon which is shown in the drawing by the horizontal line placed just above the filament of each tube.
(16) The plates of the rectifying tubes are in circuit with the middle, or plate secondary of the transformer. This secondary has a center-tap connection which divides