Elecraft KPA100 Manual - Manual (Page 51)

51
Set POWER for 11 watts. The current should increase by about 200
mA (150 mA for the KPA100 T-R switch, and 50 mA for the fan, running
at low speed). Record the new total: ________ mA. Finally, add 400 mA
(200 mA per power transistor) to this to determine the target reading for
bias setting: _______ mA.
Prepare to adjust R6 on the KPA100 (Bias Set). Make sure you're in
CW TEST mode (mode letter C flashing).
Enter TUNE mode, then adjust R6 clockwise until the current meter
shows approximately the target current recorded above. The current may
slowly drift higher, but R6 should be left at a setting that provides the
target current when you first enter TUNE mode.
Exit TUNE mode by holding any switch.
Turn the K2 off, then turn off the high-current power supply.
Disconnect the DMM and any clip leads you used for current
measurement. If you moved your DMM's (+) lead to a different tip-jack
on the meter for high-current measurement, return it to the normal (+)
jack.
Transmit Tests
Connect a 100 watt dummy load to the KPA100 antenna jack (J2).
Avoid using an antenna for initial transmit tests.
Make sure the high-current power supply is connected to the
KPA100 and is turned on.
Turn the K2 on. If you're using an antenna, switch to the band it is
resonant on, and locate an unused frequency.
Set the POWER control for about 5 watts. The KPA100 will be in
bypass mode (disabled). Select the 40-meter band.
Enter TUNE mode for a few seconds (maximum) and make sure that
the K2 (and external wattmeter, if any) indicates about 5 watts.
Select CW mode using the
M O D E
switch. Using another ham-band
receiver or transceiver, listen to your signal while sending CW.
Set the POWER control for 20 watts. You should hear the relays on
the KPA100 switch into high-power mode at the 11-watt point.
Enter TUNE mode for a few seconds (maximum) and make sure that
power output is about 20 watts. Note: The power may rise gradually to a
few watts above the intended level, the drop back slightly below it. This is
normal ALC behavior, and may happen more than once as the power
transistor bias stabilizes during key-down.
Listen to the signal quality in the second receiver while keying. The
20-watt signal should be stronger than the 5-watt signal, but the quality of
the keying and sound of the signal should be identical.
i
To protect the power transistors from high SWR, TUNE mode
initially limits power to 20 watts. To override, hold
T U N E
and
D I S P L AY
together, or turn the POWER knob after TUNE starts.
Test the KPA100 at your dummy load's rated power, up to 100
watts. Limit key-down time to a few seconds. Note: If you're using an
antenna, and the SWR is too high for a given power level, the K2/100 will
automatically reduce power. You'll see HI REFL on the LCD.
i
If you see HI CUR on the display, or if current drain seems
to be too high on several bands, you may have R26 and R27
misaligned due to the use of an inaccurate external wattmeter. (Your
actual output may be well over 100 watts.) Re-align using an accurate
wattmeter, or turn both potentiometers slightly clockwise to stay
within safe limits.
Key-down current drain is typically 12-18 amps at 100 watts,
depending on the band. You can confirm this easily if your power supply
has current metering. An alternative is to measure the DC voltage across
the current-sensing resistor, R7. Every 5 millivolts of voltage across R7
equals one amp of Q1+Q2 collector current. So, for example, a reading of
0.090 V across R7 would equal about 18 amps.