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80
RICHARDSON'S BLVEBOOK OF PROJECTION
Brown
1
lYellow
4
Violet
7
White
9
Red
2
Green
5
Gray
8
Black
0
Orange
3
Blue
6
The color of the body of the resistor is considered first, then the color of the end and lastly the color of the dot or ring at its center. The dot or ring color does NOT represent a figure, but a number of zeros. Thus, if a resistor has a red body, a blue end and a brown dot its rating m ohms is: (red) 2, (blue) 6, (brown) one zero— 260 ohms. If the dot were green, five zeros would follow the first two figures, and the value would be 2,600,000 ohms. Spme resistors are coded by three colored bands about their center, a broad band, a narrow band to one side, and. still narrower band in the center .of the broad band. These represent body, end and dot,! in the order named.
(57) Fig. 33 B has an adjustable clip for contact, so the resistance can be varied as required. Fig. 33 C is a tapped resistor, affording a choice of six resistance values. It may be used as a voltage divider.
(58) Resistors are sometimes provided with multiple tap connections, and wired through a single-pole, multiple-throw switch (see Fig. 30) by means of which the resistance can be varied as required. It may then be called a rheostat — a rheostat being a resistance unit so constructed that its resistance can easily be varied.
(59) Rheostats of the types used in connection with sound and television apparatus are shown schematically in Figs.35 A-35 E. Fig 35 A illustrates a simple rheostat connection. Fig. 35 B illustrates a three-point connection, which is preferable, since should the slider of Fig. 35 B lose contact with the coil of resistance wire, through the presence of dirt, loss of its spring tension, or other cause, the circuit will not be opened. All that will happen will be that the amount of resistance in the circuit will increase exactly as if the slider had been moved around to the left-hand end.
, (60^ It is important to avoid confusing the rheostat connection of Fig. 35 B with the potentiometer connec