Pride Amp Series Service Manual page 8

Pride DX-300 CHAPTER 2
9) For SSB operation, drive power should now be gradually increased to 10 or 12 watts, and the unit peaked for
maximum output. This can be done using the carrier insertion control on some exciters, or if this is not available,
a steady tone may be applied to the microphone input. When maximum power has been achieved, operation
consists of simply keying the microphone and speaking. The SSB delay switch should be in the on position,
which will give the R.F. actuated relays a time delay, so that they won't chatter during transmission. During the
SSB transmission, power output peaks will occur so rapidly that the output meter will not be able to follow the
signal. If a monitor scope is available, it can be seen that the peak power is considerably better than the 400
watts or so that was obtained during tune up. The SCREEN indicator will flicker with the transmission level, and
will reach full brilliance at high peak power levels. This is a faster indicator of peak drive conditions than is the
power output meter.
10) For CW operation, tune up as in step nine above. Power output will be nominal 250 watts for 5 watts of
driving power. The SSB delay switch may be left in the on position to prevent relay chatter during keying.
11) The 4CX-250B transmitting tube has been proven is commercial and military uses where long life and
reliability are major factors. Although it is designed to work a little harder in amateur service, it will still be
extremely reliable if a few common sense rules are applied.
a) Make sure that the tube always receives a good airflow. Remember that a lot of watts are being packed into
that rather small package, and that the only way to keep it cool is to get air through the tube fins. Do not block
the top of the cabinet, or stack other equipment on the amplifier. Make sure that the rear of the chassis (where
the blower gets its air) is open to cool room air. If the bottom cover of the unit has to be removed for service, see
that it is replaced properly prior to plugging in the unit (for safety also). The bottom chassis must be pressurized
in order to force air through the tube fins.
b) Wait 60 seconds before applying drive to the tube. Allowing the tube to properly warm up will help you get the
longest service from it.
c) After a long period on the air, let the amplifier run in the STANDBY mode for a minute or so before turning off
the power switch. This allows the blower to bring the tube down to a cooler temperature fairly rapidly.
d) Avoid excessive R. F. drive to the amplifier.
e) Use care in tuning most tube failures are the result of operator error, not equipment failure. These transmitting
tubes are used for thousands of hours in commercial service, and similar results should be yours with
reasonable precautions.
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