Hallicrafters SX-117, Руководство по ремонту

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5, OSCILLATORS-TEST AND EVALUATION
The normal operation of everything in the receiver train from T1 through the BFO is dependent upon the
oscillators being on frequency. This fact cannot be over stated. Extra effort getting the oscillators right will be
rewarded by better than average performance of the equipment.
Power up the equipment and allow 30 minutes warm up. All the crystal oscillators will be tested
first to allow maximum time for the VFO to stabilize. Set all SX-117 controls as follows:
The following settings will be Standard for all oscillator testing.
RF GAIN – min .
XTAL SELECTOR – NORMAL.
PRESELECTOR – doesn’t matter (dm).
BAND SELECTOR – 80 meters.
CAL RESET – ON INDEX MARK.
NL/CAL – off.
FUNCTION – LSB
SELECTIVITY – dm
NOTCH FREQ. – dm
AF GAIN – Min
5-1, OSCILLATOR DEFINITIONS
In the equipment specification and in the system schematic there are 2 oscillators referred to
as the CRYSTAL OSCILLATOR. They are V3 crystal oscillator and V13A crystal oscillator. For the
purpose of this document V3 will be referred to as the main crystal oscillator. V13A will be
referred to as the aux crystal oscillator.
5-2, SSB CRYSTAL OSCILLATOR TEST
The SSB oscillator has no adjustments to pull the xtals on frequency. The original xtals came in
matched pairs. Sets of matched pairs are no longer available (
The exact difference of 100KHz
between the USB and LSB xtals will affect the BFO adjustments to be done later
). The original designer ’s
view was that if it was off frequency, you replaced the crystals with a new matched pair. Today
your options are limited and you may have to get creative. If both xtals are low or high you can
change the values of C58 and C59 to pull the xtals up or down. Changing the tube will also pull
the xtal frequency. The goal, and important factor is the USB to LSB difference (1700KHz
–
1600KHz = 100KHz). If the xtal frequencies are off, but the difference is 100KHz the error can
be offset by the VFO CAL RESET and you can still get a zero beat on USB and LSB. Read section
6-11 in the Hallicrafters OPERATING AND SERVICE INSTRUCTIONS manual.