IF FREQUENCY 262.5 K.C.

MODEL 701 CHASSIS 16 SME

Sockets are marked for the proper tubes.

Alignment Procedure

Correct alignment is of extreme importance in all wave receivers. The receivers are properly aligned at the factory with precision equipment and realignment should not be attempted by the service technician until all other causes of faulty operation are corrected.

In order to properly realign the receiver the following equipment is necessary:

1. A signal generator which will provide an accurately calibrated signal at any frequency from 262 kilocycles to 18 megacycles. The generator should have adjustable signal output.

2. An output audio voltmeter of the low voltage type to be connected across the moving coil of the speaker. This should be capable of providing a readable deflection for relatively low output levels to avoid the effects of overload.

3. An insulated or non-metallic screw driver for the adjustment of trimmers.

IF ALIGNMENT 262.5 KC

1. Connect the output meter (low scale) across the loud speaker voice coil. Turn the wave band switch (outside of tuning knob) to its left hand or counter-clockwise position. This brings the red indicator for broadcast band to the top. Turn the volume control to its maximum position.

2. Connect the test oscillator ground to chassis and the "hot" lead from the test oscillator to the grid of the 6L7 converter tube through a series .1 Mfd. condenser. Set test oscillator to 262.5 kc.

3. Adjust IF alignment screws C13, C14, (see illustration below) of second IF transformer, T2, adjacent to rectifier tube (type 80) to maximum output, reducing output of test oscillator to keep the meter reading on scale as alignment proceeds.

4. Adjust alignment screws C11, C12, of first IF transformer, T1, (directly behind tuning condenser) to maximum output as described above.

5. Readjust these trimmers for accurate alignment. Always use the lowest possible output from the test oscillator to preclude the possibility of automatic volume control action confusing proper adjustment.

ADJUSTMENT OF WAVE TRAP

Connect test oscillator to antenna and ground terminals of the receiver using a .00025 Mfd. condenser in series with the antenna terminal. With oscillator set at 262.6 kc adjust antenna trap alignment screw C4, for minimum signal increasing output of test oscillator as a minimum is reached.

RF ALIGNMENT (Broadcast "A" or "Red" Band)

1. With test oscillator connecting antenna post through .00025 Mfd. as above set signal generator to 1400 kc.

2. Set dial scale, hour and minute hands, to 6 o'clock when gang condenser is fully meshed at maximum capacitance.

3. Set dial to calibration mark 1400 kc using hour hand to indicate frequency (no further attention need be paid to position of minute hand which is used merely for convenience in logging stations by "TIME"). Adjust broadcast oscillator trimmer condenser C15, for maximum output meter reading. If it is found that two peaks occur within the range of the trimmer action use the one in which the trimmer is in its lowest capacitance or counter-clockwise position.

4. Adjust detector input trimmer C8, to a maximum.

5. Adjust the antenna stage trimer C5, to a maximum.

6. Set test oscillator to 600 kc and tune in the signal, then adjust broadcast oscillator padder C19, for maximum output. This padder is mounted under the chassis at the side of the RF "deck." Rock the condenser back and forth a degree or two in order to obtain proper maximum.

7. Repeat the 1400 kc adjustments described under 3, 4, 5, for greater accuracy. The output of the test oscillator should always be kept at the lowest output which will allow sufficient meter swing since this assures greater accuracy of adjustment.

Short Wave "B" or "Green" Band

1. Turn the wave band switch to the "B" or "Green" position. Leave the oscillator connected as above but with its output set to 6000 kc and the .00025 Mfd. condenser replaced by a 400 Ohm resistor. Set dial scale to 6 mc on the green or middle band, adjust "B" band oscillator trimmer condenser C16, for maximum output observing as before that the proper point occurs at the minimum or counter-clockwise position of the screw if two points are found.

2. Adjust detector input "B" band trimmer condenser C9, to a maximum while rocking the tuning condenser slightly for maximum response.

3. Adjust antenna stage "B" band trimmer C6, for maximum output.

4. Set the test oscillator to 2000 kc and tune in the signal. Adjust "B" band oscillator padder condenser C18 for maximum output while rocking tuning condenser as described above.

5. Repeat operations 1, 2, and 3 to assure precise alignment

Short Wave "C" or "Yellow" Band

1. With test oscillator connected same as for "B" band and set to 18000 kc (18 mc) set dial scale to 18 mc on inner or yellow band.

2. Adjust "C" band oscillator trimming condenser C17, for maximum response. Use lower capacity or counter-clockwise response point.

3. Adjust "C" band detector input trimmer C10, to a maximum, "rocking" tuning adjustment to obtain greatest output.

4. Adjust antenna "C" band trimmer C7, for maximum response.

*The adjustment of the detector input trimmers on the "B" and "C" bands by the procedure outlined above is advisable as contrasted with the usual method of trimming without rocking the tuning adjustment because slight couplings through the tube circuits tend to disturb the oscillator frequency as the detector is tuned. This procedure should be followed on any type of all wave receiver.

In checking the circuit with a continuity or ohmmeter it is wise to follow the schematic diagram in an orderly fashion starting at the antenna and ground connections and proceeding to the speaker circuits.

See Case Page 7-16, for Dial Drive notes.

VOLTAGE CHART
Measurements from elements to chassis - 1000 Ohms per Volt Meter Line Voltage - 115V AC.
RF negative grid bias 5.0 Volts
6F6 negative grid bies 20.0 volts
AC RMS each plate of rectifier to center tax 350.0 Volts
Total current drain 82 Ma. E drop across speaker field 86.0 Volts