AMERITRON AL-572, Instruction Manual

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Ameritron AL-572 Instruction Manual
10
The left-hand meter scale indicates the grid current (Ig). The small pickets on this "Ig" scale
appear every 10 mA and the larger pickets appear every 50 mA. The full scale "Ig" reading is
250 mA.
The plate and grid meters in this amplifier normally indicate maximum grid current and
maximum RF output at or near the same "PLATE" tuning setting. Maximum grid current and
minimum plate current also generally occur at the same "PLATE" tuning setting.
Note: If the grid and plate meters always track (move together in exact step) as the tuning
controls are adjusted and if they show the same approximate amount of pointer
movement, diode D117 on the power supply board could be shorted.
D117 protects the grid current overload circuit (if used) and the meters. This diode is located near
the electrolytic capacitors on outside edge of the main circuit board. D117 will usually short if
there is a large high-voltage-to-chassis current fault. The grid and plate current meters will not
read correctly if this diode fails. If D117 is shorted the overload circuit (if used) may repeatedly
trip and grid current may appear excessively high before full power is reached.
M
ULTIMETER
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 3000 volts with the amplifier on standby. See the
"
T
RANSFORMER
C
ONNECTIONS
" section on page 15 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.