Paragraph 34 AN=08-10-112
a progressive check, stage-by-stage, should be made. To do this, couple the signal generator to the 3rd i-f tube control grid through a .1 mf capacitor. Set lhe controls and make the connections as described in Table G. Alignment Chart, 3rd i-f column. If the receiver is in proper order from the output to this stage, a signal of 60,000 microvolts from the signal generator wili provide a 10 milliwatt output level. Then couple the signal generator to the 2nd i-f and detector tubes as explained in the next two columns in the alignment chart, and check the input signal required for standard output. A faulty stage should be carefully checked for shorts, grounds and faulty components using the wiring diagrams in Scction V and Resistance Tables D and E. (8) ALIGNMENT OF I-F AMPLIFIER.—When al stages have been tested, the i-f amplifier alignment may be checked and realigning done if necessary. This is done by following the procedure as given in the Ist, 2nd and 3rd i-f columns in Table G Alignment Chart. (9) CECK AND ALIGNMENT OF C-W OSCILLATOR.—The c-w oscillator is checked and adjusted after setting the receiver controls as instructed for i-f alignment in Table G Alignment Chart. A 915 kc signal of about 30 microvolts is fed into the control grid of the Ist detector. Remove the modulation ftom the signal 
Figure 11 - Crystal Filter Coil |
generator. Turn the c-w oscillator to the ON position. Rotate the heat frequency knob to zero beat position. The arrow on this knob should be vertical and pointing upward. If it is not, loosen the set screws and set this knob properly.
If no beat note is heard, check the c.w oscillator circuit
for grounds, shorts and defective components using Test Set 1-56-A and the reading given in Table C Socket Voltages, and Resistance Tables D and E.
(10) NEUTRALIZING THE CRYSTAL CIRCUIT.—All crystal circuits are properly neutralized at the factory before being shipped. Ordinarily, reneutralizing is not required unless the neutralizing coil and capacitor (Ref. 150) or crystal and switch assembly (Ref. I60 and 167) have been replaced, or unless the crystal circuit appears to be excessively broad. If neutralizing is necessary it may be done as follows:
Disconnect the output meter and put an 0-200 microammeter in the line from the volume control (rear
section) to the second detector cathode: This is most easily done by unsoldering the lead at the volume control lug.
Set all receiver and signal generator controls as for i-f alignment. Turn the crystal control to the IN position.
Rotate the signal generator tuning knob slightly until the crystal peak is located, observing the microammeter. Tune carefully to the exact peak. Note the frequency of the generator. This will be the frequency of the crystal, which should not be more than l.3 kc above or below 915 kc.
Detune the signal generator 10 kc below the crystal frequency. For example, if the crystal frequency is 916.2 kc, tune the signal generator to 906.2 kc.
Turn modulation of signal generator off and increase the output to about 1-volt.
Extending from the neutralizing coil are two lugs A and B and two corresponding wires C and D. See Figure 11.
Extending from lug B is a wire E passing around the edge of the coil form. Increase and decrease the capacity between wires C and D by bending them closer to each other and farther apart until the microammeter reading is at a minimum. In cases where low capacity is required, cut off the wires C and D. If extreme low capacity is required, cut off lugs A and B. Also move wire E away from lug A
(11) CHECK OF HETERODYNE OSCILLATOR. Having checked the functioning of the i-f and audio amplifiers, if signals are not heard on any band, the heterodyne oscillator should be checked for oscillation,
|
|