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616 RICHARDSON'S BLUEBOOK OF PROJECTION
(which two condensers are under those circumstances in series) the current through T-2 primary is 180° out of phase with that in the primary of T-3. The drawing does not show it, but these primaries are so poled that in such case their secondary voltages will be in phase. The grid of V-4 will then become more positive (less negative) at the same time that the plate of V-4 becomes positive, which is the only time space current flows. Therefore :
Space current through V-4 increases;
Voltage drop through R-6 and R-7 increases.
Grid bias of V-l and V-2 becomes less positive.
Plate current of V-l and V-2 increases.
Saturation of the core of L-2 increases.
Impedance of L-2 declines.
Motor can speed up.
When the motor reaches a speed of 1200 r. p. m. the arms of the Wheatstone circuit are balanced and no current flows across the bridge.
If the motor speed then increases to exceed 1200 r. p. m., generating more than 720 cycles in the stationary armature, the train of events just traced is reversed. Current then crosses the bridge, but by virtue of the inductance of the coil in L-l it would lag 90° behind the current in T-3 primary, except for the action of condenser C-6, which neutralizes this effect and keeps the current in T-2 primary in phase with that of T-3 primary. By virtue of the poling of these transformers, as just mentioned, their secondary voltages are therefore 180 degrees out of phase. Therefore the grid of V-4 becomes more negative while the plate of that tube is positive, and:
V-4 space current declines.
The drop across R-6 and R-7 becomes less.
The positive bias of V-l and V-2 is less strongly counteracted.
Plate current of V-l and V-2 becomes less.
Saturation of the core of L-2 declines.
Impedance of L-2 increases. Motor slows down.