Load Box. There are two terminals labeled load. One of the terminals is additionally labeled C and the other is labeled H. There are several connections to each of these. First is the voltmeter. The H terminal connects through a 3.0 meg ohm resistor, then a 3.3 meg then another 3.0 meg to one input, cathode and anode, of a diode bridge. The bridge is labeled 1N4148. One end of the 3.3 meg ohm resistor also connects to a 7.5 meg ohm resistor. The other end of the 7.5 meg connects to one end of a .0033 microfarad 650 volt capacitor. The other end of the cap connects to the other end of the 3.3 meg ohm resistor. The other input terminal of the bridge connects to the C terminal. The negative output of the bridge, anodes, connects to the negative side of a 100 micro amp meter. The positive output of the bridge, cathodes, connects through a 750 k ohm resistor to the positive side of the meter. The H terminal connects to the wiper of a switch labeled S 1. This is an eleven position, single pole, make before break, switch. Stationary terminal 1 goes to one end of a resistor marked with a star. We will come back to the other end of this resistor later. Terminal 1 goes through another resistor to terminal 2. Terminal 2 goes through another resistor to terminal 3. This continues with the last resistor connected between terminals 9 and 10. Terminal 11 is open. There is a legend above the switch which says, quote, all 1 k ohm, 10 watt, except, star, 750 ohm, 10 watt, end quote. The free end of the star resistor goes to one of the inputs of another diode bridge. The diodes are labeled 1N4002. The other input terminal goes to the C terminal. The positive output, cathodes, goes to the positive side of the fan motor, 24 volt, 90 milli amp. The negative output of the bridge, anodes, goes to the negative side of the fan motor. The positive side of the fan motor goes to the cathode of a zener diode. The anode of this diode goes to the cathode of another zener diode. The anode of this second zener diode goes to the negative side of the fan motor. The zener diodes are labeled 1N4742A 12 volt, 1 watt, 5 percent. The fan motor is effectively in series with the 750 ohm resistor. Terminal 1 of the switch, junction of the 750 ohm and the first 1 k ohm resistors connects to one end of a 39 k ohm quarter watt resistor. The other end goes to one terminal of a neon lamp. The other end of the lamp goes to the C terminal. There is a 62 k ohm res in parallel with the lamp. This lamp is the overload indicator light. Another switch is shown which is labeled S 2 through S 12. Its wiper connects to the H terminal. A resistor marked with a star connects from terminal 1 to the C terminal. Another resistor connects from terminal 1 to terminal 2. Another resistor connects from terminal 2 to terminal 3. This continues around the switch until the last resistor is connected from 9 to 10. A legend on the switch says. Quote, resistor values, S2 through S 6, 1 k ohm, 10 watt. S7 through S9, 3 k ohm 5 watt. S10 through S12, 10 k ohm, 1 watt, except, star, 11 k ohm, 1 watt. End quote. Terminal 1 of the switch connects to one end of a 39 k ohm quarter watt resistor. The other end goes to one terminal of a neon lamp. The other end of the lamp goes to the C terminal. There is a 62 k ohm res in parallel with the lamp. This lamp is the overload indicator light. There is one overload indicator for each switch. A 100 k ohm resistor connects from the C terminal to chassis ground. A .001 micro farad, 650 volt capacitor also connects from the C terminal to chassis. This R and C are in parallel. The ammeter is not connected in any way to the other part of the circuit. The negative terminal connects to the negative of the 100 micro amp meter. The negative terminal also connects to one end of a .25 ohm 1 watt resistor. The other end of this resistor goes to the positive ammeter terminal. The positive ammeter terminal goes to one end of a 1.0 k ohm resistor. The other end of this resistor goes to the positive terminal of the 100 micro amp meter. These values give a full scale current of 800 milli amps. End verbal description.
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