ALC (Automatic Level Control)
ALC will prevent over-power operation.
The primary use of the ALC is to reduce the input drive power
to a safe level for the AL-1500. The maximum drive that the
AL-1500 will tolerate is approximately 100 watts. At this drive
level the output of the AL-1500 may be in excess of 2000 watts
when properly tuned. The ALC should be connected and
adjusted after ;he amplifier is properly tuned on CW. Use a
shielded audio-type cable with a standard male phono connector
to connect the 0-20 volt negative ALC voltage to the exciter
ALC input. Consult the exciter manual for proper connection
details.
Setting the ALC ADJ Control
Proper adjustment of the rear panel ALC control can be
achieved by the following steps:
1. Load the amplifier according to the tune-up instructions
(with the ALC disconnected from the exciter) to the desired
maximum power.
2. Connect the ALC line and rotate the ALC control fully
clockwise looking at the rear of the unit.
3. Set the MULTIMETER switch to the PO position or observe
an external PEP meter or oscilloscope
4. Set the transmitter audio control about 20
0
16
higher than
normal.
5. Speak in the microphone in a normal tone of voice and
observe the reading on the 2000 RF Watts scale
6. Adjust the ALC ADJ control on the rear panel until the
amplifier output is no more than the desired maximum
power obtained in step 1.
The exciter internal ALC will maintain linearity
the amplifier
SSB PROCEDURE
Tune the Exciter and Amplifier as described in "TUNE-UP CW
PROCEDURE".
1. Place the SSB-CW switch in the SSB position.
2. Adjust the exciter gain control to permit voice peaks to reach
the same value the peak output meter read on CW when
fully loaded. The plate and grid currents should remain well
below 50% of the CW values during normal modulation.
SSTV, FM, RTTY, PACKET, AMTOR:
The plate current should be limited to 800 mA maximum. The
grid current should be limited to 50 mA. Tune the amplifier for
peak output power with the drive reduced to the grid and plate
current below the ratings given.
NOTE:
Some exciters will put out short duration high power RF pulses
when first keyed. Exciter power output peaks may reach or
exceed full output level even if the exciter's power control has
been adjusted to deliver reduced power under "keydown"
conditions.
The amplifier loading control must be set high enough
(clockwise) to prevent extremely high energy levels from
developing in the plate and grid circuits of the amplifier. DO
NOT "UNDERLOAD" THE AMPLIFIER TO REDUCE
POWER. Never "retune" the amplifier to produce higher ef-
ficiency with reduced drive. Poor linearity, splatter or even
damage to components may result from failure to follow these
instructions. Repeated tripping of the grid current circuit
usually indicates that the loading control is set too far counter-
clockwise for the amount of drive being applied to the amplifier
or that something in the antenna system is :hanging impedance
(arcing) during peaks.
WARNING!!
MAKE NO ATTEMPT TO PUT THIS AMPLIFIER IN SERVICE WITH THE COVER REMOVED!
CONTACT WITH VOLTAGES INSIDE THIS AMPLIFIER CAN BE FATAL! ALWAYS
DISCONNECT THE AMPLIFIER FROM THE POWER MAINS AND WAIT FOR THE FILTER
CAPACITORS TO DISCHARGE BEFORE REMOVING THE COVER.
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