Tune-Up Procedure - QRO Technologies HF-2500DX Instruction Manual

TUNE UP PROCEDURE
Before making any tune up procedures, make sure your amplifier is connected to an
appropriate load capable of handing at least 1,500 watts of power. Failure to do so may
result is serious damage to your amplifier.
When the two minute warmup cycle has been completed, the red power light will turn on. The
amplifier is now ready for tune up. At this point, place your transceiver in the SSB mode with the
mic gain at minimum. Put the amplifier's Operate/Standby switch in the operate position. Key your
transceiver and you should notice the green transmit LED on the amplifier lite. You should also
hear the amplifier's internal relays latch. With the transceiver keyed and the amplifier's Multimeter
switch in the IP position, observe the plate current (IP). It should be in the neighborhood of
.400 - .500 amperes more or less. Also, your screen current should indicate a negative reading.
In other words, it will move to the left. This is normal. Unkey your transceiver, and place the
amplifier in the standby mode.
TUNEUP OBJECTIVE: The objective of the tuneup procedure is to bring the amplifier to
resonance by adjusting the tune & load controls for the proper level of screen current. You will
adjust tune control so the screen current peaks on the screen current scale. You will also adjust
the load control to bring the screen to the proper level. When tuning on 160 meters and 80
meters, you may notice the screen current drift downwards. This is a result of the padder
capacitors on the load side warming and changing their values. We are not concerned about an
absolute steady state of screen current. We simply want you to get the screen current to peak on
scale and adjust the load control for the specified level of screen current (50 mA). When re-keying
after tuneup, the screen current may initially exceed 50 mA. This is OK because the screen
current will reduce to 50 mA. The amplifier will go into the fault state if the screen current goes
to a dangerous level.
1. Place your transceiver in CW mode, and set its output power level to 30 wattts for 160, 80, 40
meters and 20 watts for 20, 15, 10 meters.
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2. Place the amplifier in the operate position. Make sure the Tune & Load controls are set at zero.
3. Key your transceiver, and you should notice the screen current meter move to the left indicating
negative current. Again, this is normal. Advance the loading control clockwise until you see a
slight rise in screen current. If you do not see this rise, adjust the tune control clockwise to
the 50 position and then adjust the load control for a reading of 10 or 20 mA. You may see
the screen current dip to the left. Keep advancing the load control clockwise, and the
screen current will continue to rise.
4. Turn the tune control clockwise until the screen current reads 50 - 100 mA. If the screen
current goes full scale, turn the tuning control counterclockwise until the screen current meter
reads between 50 - 100 mA. If the screen current should rise to a dangerous level, the amplifier's
protection circuit will place the amplifier into a fault state, and the red fault button light will come
on. If this occurs, readjust the tune control counterclockwise, and push the fault light button to
reset the amplifier, and start again.
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