Schematic of the low resistance adapter. Part 1, the power supply. There are two possibilities for the power transformer. 1. There are two transformers. The 120 volt primaries are connected in parallel and the 12 volt secondaries are connected in series. The point where the two secondaries connect together is the center tap. 2. A single transformer having a 24 volt secondary winding has a center tap on that winding. Circuit. The wide (neutral) prong of the line plug goes to the bottom end of the power transformer primary winding. The narrow (hot) prong of the plug goes to one terminal of the on/off switch, an S P S T. The other terminal of the switch goes to one terminal of a fuse and the other end of the fuse goes to the top end of the transformer primary. The fuse is labeled 1/2 amp. The center tap of the transformer secondary goes to common and chassis ground. The two ends of the secondary go to the AC terminals of a standard bridge rectifier. The positive output of the bridge goes to the positive end of a 100 microfarad electrolytic capacitor. This point is labeled V plus. The negative end of this capacitor goes to ground. The negative output of the bridge goes to the negative end of a 500 microfarad capacitor and this point is labeled V minus. The positive end of the capacitor goes to ground. The V plus point goes to the input terminal of a 7812 voltage regulator I C. The ground terminal goes to ground and the output goes to a point labeled plus 12 V. The V minus point goes to the input terminal of a 7912 regulator I C. It's ground terminal goes to ground and its output terminal goes to a point labeled minus 12 V. There are 0.1 microfarad caps connected from the input terminal of each I C to ground and from the outputs of each I C to ground, 4 in all. The plus 12 v point connects to the positive end of a 25 microfarad cap and the other end is grounded. The minus 12 v point connects to the negative end of a 25 microfarad cap and the other end is grounded. Part 2. The current source excitation. The cathode of a 1N4148 diode goes to minus 12 v and the anode goes to the anode of a 1N756A 8.2 volt zener diode. The cathode goes through a 1 k ohm 1/2 watt resistor to plus 12 v. The junction of the resistor and zener go to the base of an N P N transistor labeled Q1. The collector of Q1 goes to binding post labeled minus unknown excitation. The emitter of Q1 goes to the rotor of the range switch. The 0.2 ohm position of the switch goes through 3 20 ohm 1/4 watt resistors in series and then to a 50 ohm trimming pot connected as a rheostat. The other end of the rheostat goes to minus 12 v. The 2 ohm switch position goes through a 560 ohm resistor then a 500 ohm rheostat to minus 12 v. The 20 ohm switch position goes through a 5.6 k ohm resistor then a 5 k ohm rheostat to minus 12 v. The CAL position of the switch does not connect to anything. The binding post labeled plus unknown excitation is connected to ground. Part 3. The voltmeter section. The binding post labeled minus unknown voltmeter goes to the operate position of deck A of the calibrate switch, a 3 deck 3 position switch. The binding post labeled plus unknown voltmeter goes to the operate position of deck B of the calibrate switch. The rotor of deck A of the calibrate switch goes through a 1 k ohm trimming pot connected as a rheostat and then through a 3.6 k ohm resistor to the inverting input, pin 2, of a 741 op amp. The rheostat is labeled gain set. The rotor of deck B goes through a 3.9 k ohm resistor to the noninverting input, pin 3, of the op amp. Pin 3 also goes through a 39 k ohm resistor to ground. Pin 2 of the op amp goes through the parallel combination of a 39 k ohm resistor and a 4.7 microfarad cap to the output, pin 6. The plus side of the cap goes to the output. There is a 4.7 k ohm resistor from pin 6 to ground. Pin 6 also goes to the operate and gain set positions of deck C of the calibrate switch. The rotor of deck C goes to the positive output binding post labeled to DMM. The negative output binding post is grounded. Pin 7 of the op amp goes to plus 12 v. Pin 4 goes to minus 12 v. A 10 k ohm trimming pot labeled rough zero has its wiper connected to minus 12 v. One side goes through a 1 k ohm resistor to pin 5 of the op amp. The other side of the rough zero pot goes through a 510 ohm resistor then a 2 k ohm pot connected as a rheostat to pin 1 of the op amp. This rheostat is labeled front panel zero adjust. Part 4. The calibrator section. One end of a 200 ohm trimming pot labeled calibrator is grounded. the other end goes through a 20 k ohm resistor to minus 12 v. The wiper goes to three terminals of the calibrate switch. they are, The cal set positions of decks A and C and the gain set position of deck A. Just as a reminder the gain set position of deck C goes to the output of the op amp. The gain set and cal set positions of deck B are grounded. This completes the verbal description of the schematic diagram.