AL-80B Instruction Manual
6
Multimeter
The multimeter is the meter on the right. It continuously reads the forward
peak envelope power
on
its left-hand scale (FWD). This scale is calibrated in 100 watt steps up to 2 kW.
The right-hand scale of this meter provides four metering functions that are selected by the
"MULTIMETER" switch. These functions include the measurement of high voltage (HV), reflected
power and SWR (REF), ALC voltage output (ALC), and relative ALC threshold (ALC SET). The
MULTIMETER FUNCTIONS section that follows describes these functions in more detail.
Multimeter Functions
HV
:
The multimeter indicates the dc plate voltage applied to the PA tube when the
MULTIMETER switch is placed in the HV position. The correct scale to use is the
ALC/ HV scale. This scale has a picket every 100 volts. Two zeros must be mentally
added behind the numbers indicated on the meter scale (i.e. multiply by 100), so that
"25"=2500 volts and "20"=2000 volts. Do not operate the amplifier if the high voltage
is over 3200 volts with the amplifier on standby. See the "Transformer Connections"
section on page 12 for information on correcting excessive high voltage.
REF
:
The multimeter measures the antenna (or load) peak envelope reflected power and the
SWR when the MULTIMETER switch is placed in the REF position. The full scale
reflected power reading is 500 watts. This scale is marked every 10 watts below 100
watts, and every 100 watts from 100 to 500 watts.
Note:
The SWR of the load is measured when the "MULTIMETER" is in the REF
position by observing the different red SWR curves. The forward and reflected
power meter pointers will cross each other on, or near, the correct SWR curve.
ALC
:
The multimeter measures the output voltage of the ALC detector when in the ALC
position. The full scale ALC reading is 35 volts and is read directly from the ALC/ HV
scale. The meter should flick upwards occasionally during normal ALC action. See
ALC Circuit operation on page 15 for more information.
ALC SET
:
The multimeter measures the
approximate
grid current that will produce ALC activity
when the meter switch is in the ALC SET position. One zero must be added to the
reading on the ALC/ HV scale for this function. For example, ALC action will begin
at approximately 150 mA of grid current (typically between 120 mA and 180 mA)
when the "ALC SET" control is adjusted until the meter reads "15."
Summary of Contents for AL-80B
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