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  1. Disable the screen circuit of the pa tubes by unsoldering one end of the jumper hetween PA DISABLE jacks J5 and J6

  2. connect a 50-ohm, noninductive, 100-watt dummy load to RF OUT jack J1.

  3. Connect a vtvm rf probe across the 50ohm dummy load.

  4. Set the OFF-ON-NB-CAL switch to ON; set the BAND switch to 28A; and set the EMISSION switch to LOCK and the tuning dial to 100. Set the meter switch to GRII).

  5. Advance the MIC GAIN control as necessary and adjust the EXCITER TUNING control for maximum grid current.

  6. Adjust the P. A. TUNING control for a maximum rf voltage indication on the vtvm. Adjust the MIC GAIN control to keep this indication below 0.5 volt.

  7. From the bottom of the chassis, adjust pa neutralizing capacitor C184 (figure 6-3) for a minimum rf indication on the vtvm. This voltage is the pa plate circuit feedthrough and is minimized by neutralization.

  8. Remove the vtvm rf probe from the dulnmy load, reconnect the jumper between the PA DISABLE jacks, and reconnect the highvoltage lead to the power supply.

4.6.13 Driver Neutralizing

  1. Set the OFF-ON-NB-CAL switch to OFF. Removeheater voltage from driver tube V8 by unsoldering L29 from C241 (figure 6-3), or, if an old 6CL6 tube with no short cirruits is available, clip off its filament pins and substitute it for V8.

  2. Connect rf probe to dummy load. Set ON-NB-CAL switch to ON, BAND switch to 28A, and tuning dial to 100. Set EMISSlON switch to LOCK and meter switch to PLATE.

  3. Increase IiIIC CAIN setting, and adjust F ECITER TUNING AND P. A. TUNING colltrols for maximum voltnge across dummy load. This level should be less than 0.3 volt.

  4. Adjust driver neutralizing capacitor C117 for a voltage dip. This capacitor is located on the shield partition closest to the shield can. Refer to figure 6-3.

  5. Set the OFF-ON-NB-CAL . switch to OFF, and replace V8 in its socket.

  4.6.14 Feedback Neutralizing.

  1. Set BAND switch to 28A position and tuning dial to 100, EMISSION switch to TUNE. and meter switch to PlATIE position.

  2. Adjust EXCITER TUNING control for a peak in pa plate current.

  3. Dip the pa plate current with TUNING control.

  4. Switch to LOCK and repeat steps b and c.

  5. Adjust feedback neutralizing capacitor C120 (on driver-pa shield below ehassis and farthest from shield cans, figure 6-3) until pa plate current dip and grid current dip coincide. Readjust the MIC GAIN as necessary to hold pa grid current at about halilscale during this adjusiment.

  6. Set BAND switch to 21.2, peak EXCITER TUNING control, and dip pa plate current with P. A. TUNING control.

  7. Check that pa plate current dip and grid current dip occur at same setting of P. A. TUNING control.

  8. Repeat this check on bands 14.2, 7.0, and 3.

4.6.15 PA Loading Trimmer Adjustment

These trimmer capacitors are adjusted to provide the required total output capacity for matching 50-ohm antenna loads on the amateur bands with the INCR LOAD control set at the 50 W mark. Normally, they will not need readjustment since, when the pa is properly loaded, the tuning is relatively broad. If it is determined that adjustment is necessary. procteed as follows:

  1. Refer to figure 7-2 for location of the loading trimmers.

  2. Connect a 50-ohm nonreactive dummy load to the transceiver RF OUT jack.

  3. Set INCR LOAD conlrol to 50 W mark.

  4. Tune to 21.3 MHz, and set EMISSION switch to lock.

  5. Set MIC GAIN to the point that begins to produce pa grid current. This is grid current threshold.

  6. Adjust (C155 until pa draws 230-mA plate current at the dip

  7. Tune to 28.6 MHz, and check plale current. If not 230 mA, readjust C155 for best compromise between 21.3 and 28.MHz.

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