AMERITRON AL-572 Instruction manual

Ameritron AL-572
Instruction Manual
Table of Contents
Introduction ................................................................................................................................. 1
Unpacking Instructions................................................................................................................ 2
Features ....................................................................................................................................... 3
AL-572 Technical Specifications ................................................................................................ 4
Input ................................................................................................................................ 4
Output.............................................................................................................................. 4
Efficiency ........................................................................................................................ 4
Power Supply .................................................................................................................. 4
Tube................................................................................................................................. 5
Metering .......................................................................................................................... 5
ALC ................................................................................................................................. 5
Relay................................................................................................................................ 5
Connectors....................................................................................................................... 5
Physical ........................................................................................................................... 5
General Information .................................................................................................................... 6
Safety Interlock ............................................................................................................... 6
Peak Envelope Power vs. Average Power....................................................................... 6
Circuit Descriptions..................................................................................................................... 7
ALC ................................................................................................................................. 7
Dynamic Bias .................................................................................................................. 7
Wattmeter Circuit............................................................................................................ 8
Power Supply .............................................................................................................................. 8
Filament Supply .............................................................................................................. 8
Plate (HV) Supply ........................................................................................................... 8
Meters.......................................................................................................................................... 8
Current Meter (plate and grid)......................................................................................... 8
Multimeter....................................................................................................................... 9
Multimeter Functions .......................................................................................... 9
HV ........................................................................................................... 9
REF.......................................................................................................... 9
ALC ......................................................................................................... 10
ALC SET................................................................................................. 10
Tube Life ..................................................................................................................................... 10
Export Modifications .................................................................................................................. 11
Technical Assistance ................................................................................................................... 12
Notes................................................................................................................................ 12
Installation Guidelines And Suggestions .................................................................................... 13
Location Of The Amplifier.............................................................................................. 13
Ventilation....................................................................................................................... 13
Power Connections.......................................................................................................... 13
Grounding........................................................................................................................ 14
Transformer Connections ................................................................................................ 15
Interconnections .......................................................................................................................... 16
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Operating Instructions And Guidelines ....................................................................................... 16
Front Panel Controls........................................................................................................ 16
"MULTIMETER" Switch ................................................................................... 16
"OFF-ON" Switch ............................................................................................... 16
"STBY-OPR" Switch .......................................................................................... 16
"PLATE" Control ................................................................................................ 17
"LOAD" Control ................................................................................................. 17
ALC Metering, Controls, and Adjustments..................................................................... 17
ALC Metering Functions..................................................................................... 17
ALC ......................................................................................................... 17
ALC SET................................................................................................. 18
ALC Controls ...................................................................................................... 18
ALC Adjustments................................................................................................ 18
SSB Operation......................................................................................... 18
CW Operation ......................................................................................... 18
Rear-panel "ALC LIMIT" control ....................................................................... 19
ALC Limit Adjustment (rear panel) .................................................................... 19
Driving Power ................................................................................................................. 20
Tube and Component Life............................................................................................... 20
Tuning ............................................................................................................................. 21
Tuning Procedure ................................................................................................ 22
"ALC SET" control ............................................................................................. 24
Additional SSB Notes ..................................................................................................... 25
AM (Amplitude Modulation) Operation ......................................................................... 25
Audio Distortion.............................................................................................................. 25
FM (Frequency Modulation), RTTY, and DIGITAL OPERATION .............................. 26
QSK Operation................................................................................................................ 26
Periodic Maintenance.................................................................................................................. 26
Parts List...................................................................................................................................... 28
Power Supply / SWR Board (50-0057-1)....................................................................... 28
Tuned Input Board (50-0057-2) ...................................................................................... 29
AL-572 Tuned Input Chart.............................................................................................. 29
Meter Board (50-0057-3) ................................................................................................ 29
Timer / Overload Board (50-0057-5) .............................................................................. 30
AL-572 Main Chassis Parts List ..................................................................................... 31
AL-572 Wiring Diagram ............................................................................................................. 32
Power Supply / SWR Board Schematic .......................................................................... 33
Tuned Input Board Schematic......................................................................................... 34
Meter Board Schematic ................................................................................................... 35
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Ameritron AL-572
Instruction Manual
Ameritron AL-572
1300 watt PEP Linear Amplifier Instruction Manual
INTRODUCTION
The Ameritron AL-572 is a 1000 watt CW, 1300 watt PEP (nominal output power) linear
amplifier that operates on all Amateur bands from 160 through 15 meters (WARC bands and ten
meters with reduced performance). The AL-572X and AL-572Y are export models that operate
from 160 through 10 meters.
The AL-572 uses four 572B tubes in a class AB2 grounded grid circuit. High-quality power
supply and RF components combine with an accurate peak-detecting directional coupler, front
panel adjustable true ALC circuit, and automatic bias switching to make this the best featured
and most reliable 572B amplifier available. The AL-572 and AL-572Y are factory-wired for 120
volt, 50/60 Hz ac line voltage. The AL-572X is factory wired for 240 volts. All models are easily
converted to other supply voltages between 90 and 250 volts ac.
DANGER:
NEVER APPLY POWER TO THIS AMPLIFIER WITH THE COVER
REMOVED!
CONTACT WITH THE VOLTAGES INSIDE THIS
AMPLIFIER CAN BE FATAL!
PLEASE READ THIS MANUAL BEFORE ATTEMPTING TO OPERATE EQUIPMENT!
WARNING:
Improper or abusive operation of this amplifier can
damage the tubes or other components in this amplifier.
Damage caused by improper or abusive operation is not
covered under the warranty policy.
Ameritron
116 Willow Road
Starkville, MS 39759
(662) 323-8211
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Ameritron AL-572
Instruction Manual
UNPACKING INSTRUCTIONS
Remove the AL-572B tubes from their shipping cartons. Carefully inspect each tube for visible
damage. Look for bent or broken pins. Roll each tube over slowly while listening and watching
for loose internal materials. Contact either your Ameritron dealer or Ameritron immediately if
any damage exists.
Carefully lift the amplifier from the shipping carton, and place it on a firm, level surface. Inspect
the amplifier for shipping damage. Contact either your Ameritron dealer or Ameritron
immediately if any damage exists. Remove the cover screws with a #2 Phillips screwdriver.
Save the screws to re-secure the cover. Carefully lift the rear of the cover while sliding the cover
back. The AL-572 is shipped with the fuses and fuse caps packed inside the amplifier.
Additional screws will be included in the fuse pack when required.
DANGER:
Never remove the cover while this amplifier is connected
to the power mains! Contact with the voltages in this
amplifier can be fatal.
The tubes must be installed in their sockets prior to operation. Observe the pin configuration on
each tube and socket. Two of the of the four base pins are slightly larger in diameter. Carefully
observe the pin alignment to be sure correct tube pins are centered on the socket's holes. Firmly
press the tubes into the socket. Do NOT twist or force the tubes into their socket.
Install the anode connector on the tube's anode terminal.
Install the fuses and fuse caps on the back of the amplifier. This amplifier uses two 20A fuses for
standard 120 Vac operation (models B and BY) or two 12A fuses for 240 V operation (model BX
only). If you wish to operate the amplifier on a line voltage other than 120 volts, the jumpers on
the power transformer primary windings must be changed. If the primary wiring is changed, the
correct fuses must be installed. See the "TRANSFORMER CONNECTIONS" section on page 15 for
more information.
CAUTION: Always use fast-blow fuses rated at 250 volts or
higher.
NEVER use standard automotive glass fuses or
slow-blow fuses.
The top cover should now be installed with the ventilation holes on side of the cover positioned
near the electrolytics. The ventilation holes on the top of the cover should be on the right side of
the amplifier (front view). Secure the cover by installing the corner screws first. Install all the
screws loosely until every screw is in place. Tighten the screws after they have all been
installed.
Note: Ameritron will NOT be responsible for shipping damage due to improper packing.
The packing materials used to ship this amplifier are specially designed to prevent damage. All
packing materials should be retained for future shipping. Replacement packing materials may be
purchased from Ameritron if original packing materials are unavailable.
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Instruction Manual
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FEATURES
+ The AL-572 uses rugged inexpensive 572B tubes.
+ The 572B requires only a few seconds of warm-up time.
+ A dynamic bias circuit eliminates hundreds of watts of unnecessary heat generation in the
power amplifier tubes. The result is cooler operation and longer component life.
+ A multi-voltage heavy-duty transformer with a unique "buck-boost" winding allows
adjustment of the primary voltage to 14 different voltages centered on 115 and 230 volts. This
versatile Ameritron feature allows the user to select the optimum primary voltage for
maximum performance and life.
+ The tuning and loading controls have vernier 6:1 reduction drives for smooth tuning.
Logging scales allow quick and repeatable control adjustments for rapid band changes.
+ The AL-572 has two illuminated cross-needle panel meters. The left meter provides a
continuous reading of grid and plate currents. The right meter reads peak RF power output on
one scale and Plate Voltage (HV), Reflected power and SWR (REF), ALC detector voltage
(ALC), and ALC adjustment level (ALC SET) on the other scale.
+ Filament and plate voltages are maintained using the "STBY/OPR" switch. This allows the
amplifier to be conveniently bypassed for "barefoot" operation.
+ A front panel "ALC SET" control allows convenient adjustment of the ALC threshold. The
unique ALC circuit samples the grid current and power supply voltage.
+ An "XMT" LED on the front panel indicates proper keying of the amplifier by the exciter.
+ A rear panel "12 V" auxiliary output jack provides up to 200 mA at 12 Vdc for accessories
such as the ATR-15 Antenna Tuner.
+ A step-start circuit limits the inrush current to the power supply and tube filament. This
circuit extends the life of the amplifier components.
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AL-572 TECHNICAL SPECIFICATIONS
INPUT
Circuit type:............................................................... Pi-network, slug tuned coils
Maximum VSWR at resonance:................................ 1.3:1 or less
Minimum 2:1 VSWR bandwidth: ............................. typically 15% of center frequency
Maximum SSB drive power permissible: ................. 110 watts PEP
Typical drive for full CW power output:................... 75 watts
OUTPUT
Circuit type:............................................................... Pi-L, Pi-network
Typical SSB PEP voice operation:............................ 1300 watts nominal
CW continuous operation:......................................... 1000 watts nominal
1/2 hour PEP two-tone test:....................................... 1000 watts
1/2 hour continuous carrier (RTTY): ........................ not rated, contact factory for specification
Frequency Coverage:................................................. 1.8 to 21 MHz amateur bands. (Export
models include 24.5 and 28 MHz at reduced
power. WARC bands available at reduced
power)
Third Order IMD:...................................................... -34 dB or better (below PEP at rated output)
EFFICIENCY
CW ............................................................................ approximately 61%
SSB............................................................................ approximately 65% (envelope crest)
POWER SUPPLY
Circuit type:............................................................... Full wave voltage doubler
No load voltage: ........................................................ 2900 V
Full load voltage:....................................................... 2500 V
Full load current: ....................................................... .7 A
NL to FL Regulation: ................................................ 14% or less internal voltage drop
Transformer:.............................................................. 21 lbs
Capacitors:................................................................. 26 mFd total, computer grade
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Normal line current at rated CW output:................... 16 A at 120 Vac
Normal line current at 1300 watt PEP output: .......... 8 A average at 120 Vac
Power line current in standby:................................... 2 A at 120 Vac
TUBE
Type:.......................................................................... (4x) 572B
Continuous dissipation:............................................. 640 watts
Warm-up time: .......................................................... 3 seconds
METERING
Multimeter:................................................................ Peak forward power (continuously). The
second scale switches between peak
reflected power (and SWR), ALC threshold,
ALC output voltage, and high voltage.
Current meter: ........................................................... Plate and grid current (simultaneously) on
separate scales.
ALC
Negative going, 0 to 10 volts, adjustable.
RELAY
Requires contact closure or sink of +12 Vdc at 100 mA. Back pulse protected.
CONNECTORS
RF:............................................................................. SO-239
Line: .......................................................................... NEMA 5-15P, standard 120 V three wire
Others: ....................................................................... RCA Phono
PHYSICAL
Dimensions:............................................................... 15-1/2" D x 14-1/2" W x 8-1/2" H
Weight: ...................................................................... 40 lbs.
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GENERAL INFORMATION
SAFETY INTERLOCK
An interlock switch is closed while the amplifier's top cover is in place. This switch completes
the primary circuit of the power transformer. The interlock will open and de-energize the
transformer primary if the top cover is removed.
DANGER:
High voltage can kill!
Accidental contact with the
voltages in this amplifier can be lethal.
For your personal safety please observe the following precautions:
1. NEVER defeat the interlock.
2. NEVER remove the cover with the amplifier connected to the power line.
3. ALWAYS allow the capacitors to discharge for several minutes after unplugging the
amplifier and before removing the cover.
4. ALWAYS select the high-voltage (HV) function of the Multimeter to check the high voltage
potential. Do not remove the cover if voltage is indicated.
5. ALWAYS ground the tube anode (top metal connector) to the chassis through a low value,
high wattage resistor before touching anything inside the amplifier.
6. ALWAYS be cautious of heat. Many components inside the amplifier operate at high enough
temperatures to cause burns.
7. NEVER make any unauthorized component or circuit modifications to this product. The
only acceptable source for modifications is Ameritron or a source approved by Ameritron.
Unauthorized modifications almost certainly will increase the risk of equipment failure or
personal injury.
PEAK ENVELOPE POWER VS. AVERAGE POWER
Peak envelope power (PEP) is often misunderstood by amateurs. PEP is not associated with the
sine wave or root-mean-square (RMS) power, and PEP has no fixed ratio to average power on
any mode except FM, FSK or CW. It is impossible to use a formula or "rule of thumb"
approximation to convert between average and peak voice waveform powers.
PEP is the power at the crest (highest point) of the RF envelope waveform. On SSB, the average
power can vary from a few percent to more than half the PEP produced. Generally, PEP on SSB
is two to five times greater than the average power. A 50 watt average power SSB signal could
produce PEP levels from below 100 watts to more than 250 watts.
On CW and other constant amplitude modes (such as FM or RTTY), the PEP is always equal to
the average power. For example, on CW, FM, or RTTY 1000 watts of average power produces
exactly 1000 watts of PEP.
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CIRCUIT DESCRIPTIONS
ALC
The AL-572 is one of the few amplifiers using a "true" automatic level control (ALC) circuit. In
this amplifier, the ALC actually samples grid current and power supply loading to determine the
ALC voltage. The front panel "ALC SET" knob adjusts the level of grid current where ALC
action begins. ALC action begins softly over a range of a few milliamperes to minimize
distortion. This soft-touch ALC is an Ameritron exclusive.
The ALC circuit is located on the METER BOARD P/N 50-0080-3 (behind the
"MULTIMETER" switch). IC301 (pins 9 and 10) compares the voltage drop (caused by grid
current) across R106 in the main power supply board. ALC voltage is derived by comparing the
grid shunt voltage to the voltage from the power supply.
The pin 8 output of IC1 will go negative if the grid shunt voltage exceeds the voltage from
divider R311 and R2 (chassis mounted control), or if the supply voltage sags from excessive line
voltage drop. Pin 8 is followed by current buffer Q303 that sources the negative ALC voltage to
the ALC output jack.
This amplifier includes an ALC Limit control on the rear panel. This control reduces overshoot
and eliminates motorboating (a slow rhythmic fluctuation) in the transmitted signal. These
problems are caused by excessive transceiver ALC attack time delay. This control sets the
maximum voltage level available from the ALC circuit. Adjustment details begin on page 17.
DYNAMIC BIAS
Conventional bias circuits force high power linear amplifiers to dissipate hundreds of watts
during low or no signal periods. This creates needless heat, since virtually no dissipation is
required unless the amplifier is being driven with large signal levels.
The AL-572 contains an exclusive bias circuit that reduces the idling (quiescent) current very
close to the tube's cut-off region. The power amplifier tube in the AL-572 has a full resting
period of very low dissipation between dots and dashes on CW and between words on SSB. The
lower idling current reduces component temperature on both CW and SSB. If only a few
milliwatts of RF power are applied to the amplifier, the quiescent current will increase. Linearity
remains excellent with this circuit because the tube can remain biased for class AB operation
without unnecessary standing dissipation.
The dynamic bias circuit is located on the Power Supply Board P/N 50-0080-1. Diodes D101
and D102 rectify a small sample of the RF drive voltage. This voltage is applied to the base of
dc switch Q101. If Q101's base is driven with a few microamperes of current from the RF
sampling circuit, Q101's collector will pull the base of PNP transistor Q102 low. This turns dc
switch Q102 on.
When Q102 is on, zener diode D103 is connected between the collector and base of Q103.
D103 sets the operating bias. This zener applies forward bias to Q103's base whenever the
collector voltage of Q103 exceeds the voltage of D103. This forward bias will turn Q103 on
harder and will reduce the collector voltage. If the collector voltage is less than the breakdown
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Ameritron AL-572
Instruction Manual
voltage of D103, Q103 will move towards cut-off and the collector voltage will increase. Q103
functions as a current buffer for zener diode D103.
WATTMETER CIRCUIT
The AL-572 wattmeter circuit uses an accurate directional coupler followed by a true peak
detector circuit. This circuit will accurately determine the true peak envelope power (PEP) of
normal voice waveforms. If the load SWR is high, the true power reading will be obtained by
subtracting the reflected power from the forward power.
POWER SUPPLY
FILAMENT SUPPLY
The filament circuit of this amplifier satisfies all requirements of the tube manufacturer related to
tube performance and life. The filament voltage and inrush current are controlled by the power
transformer's internal resistance and impedance, filament choke resistance, filament wiring
resistance, and the step-start circuit. NEVER replace any circuit components or wiring with
substitute parts. This precaution will insure maximum life for the tube.
PLATE (HV) SUPPLY
The plate supply uses a full wave doubler circuit with 200 amp surge rated diodes and a heavy
duty 21 pound transformer. Filtering is accomplished by a bank of high quality computer grade
capacitors totaling 26 mFd. Large 50k ohm, 7 watt bleeders are used for safety and superior
voltage equalization. The transformer allows user selection of fourteen different line voltages
(see the "TRANSFORMER CONNECTIONS" section on page 15 for details).
Power is supplied through "OFF-ON" switch S2. A 10 ohm resistor (R27) limits the line current
during the filter capacitor charge time to lower component stress. When the filter capacitor
charging current decreases sufficiently, RLY102 shorts the 10 ohm resistor. This applies full
power line voltage to the transformer. The 10 ohm resistor is protected from high-voltage supply
shorts by a 2A slow-blow fuse (F101) during start-up. If F101 or the 10 ohm resistor (R27) fails
the amplifier will not start. If F101 fails from a momentary HV to ground fault, meter protection
diode D117 may also fail. See the "Metering Functions" section that follows for more
information.
METERS
CURRENT METER (PLATE AND GRID)
The plate and grid current meter is located on the far left side of the front panel. This meter
indicates the plate current (Ip) on the right-hand meter scale. This scale has a small picket every
25 mA, a large picket every 100 mA, and indicates 1000 mA at full deflection.
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Ameritron AL-572
Instruction Manual
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.
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 3000 volts with the amplifier on standby. See the
"TRANSFORMER CONNECTIONS" 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.
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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.
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."
TUBE LIFE
The 572B is a reasonably rugged tube. The likelihood of premature failure can be reduced by
avoiding excessive tube element temperatures. Element temperature is a function of the duration
and the amount of power dissipated. The elements in the 572B have very good immunity to short
term overload failures.
The anode in the 572B can tolerate large dissipation overloads for short periods of time due to
the thermal mass of the anode. Anode color is a good indication of incorrect tube operation. The
anode in the 572B is designed to operate at moderate temperatures. These temperatures normally
do NOT produce anode color.
The graphite anode is coated or mixed with a "getter" material that de-gasses the tube. This
material is activated by normal operating anode temperatures. The likelihood of gas failure (tube
arcing) is reduced by operating the 572B tubes on a regular basis at normal ratings.
Care must be taken to avoid exceeding the temperature ratings of the tube's glass-to-metal seals.
The life of the tubes in this amplifier may be prolonged if tuning periods are kept short and a
brief "cool-down" periods are provided between tuning periods. Try to allow a one or two minute
non-transmitting "cool-down" period after lengthy CW or RTTY transmissions before shutting
off the AC power switch.
Incorrect operation is most likely to damage the tube's control grid or anode. Applying full drive
power for several seconds with excessively "light" loading (indicated by abnormally high grid
current) can cause control grid damage. Several seconds of high drive power operation with
improper tuning or excessively "heavy" loading (indicated by low output power in concert with
normal plate current) can melt or damage the anode. These undesirable operating conditions can
be avoided by following the tuning procedures in this manual.
In the AL-572, a grid current of 200 mA (at 100 watts of drive) produces rated grid dissipation.
For maximum tube life, the short-term average grid current and drive power should always be
kept below these values.
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Ameritron AL-572
WARNING:
Instruction Manual
NEVER drive this amplifier with more than 100 watts of
short term average envelope power.
NEVER allow the
grid current to exceed 200 mA under any operating
condition.
Maximum power output normally will occur with approximately 125 mA of grid current on CW,
or less than 45 mA of grid current (125 mA instantaneous peak) on SSB (two-tone test). Grid
dissipation, with 125 mA of grid current and 70 watts of drive, is approximately ten watts.
If you wish to add control grid protection to the AL-572, always remember fuses and resistors are
too slow and unpredictable to adequately protect tubes. While grid protection is generally not
required with tubes like the 572B, Ameritron does offer an optional fast-acting electronic circuit
that will rapidly disable the amplifier if excessive grid current occurs. This circuit also reduces or
eliminates the chance of tank component damage from incorrect loading or load failure. The part
number of this add on board is 50-0080-5.
The continuous commercial plate current rating of each 572B is 275 mA. For maximum tube life,
total plate current should be maintained below 1100 mA on CW and other "steady" carrier
modes. Brief periods of plate current exceeding 1100 mA will not cause loss of emission or
shorten the amateur service life of the tubes in this amplifier.
The application of filament voltage causes thermal stresses from rapid and uneven temperature
changes. Avoiding needless cycling of the filament can prevent premature failure or unnecessary
stress in the tube's filament.
An accumulation of gas (or stray debris) in the tube can cause the tube to arc between the anode
and the other elements of the tube. The resulting "gas arc" will generally manifest itself as a loud
"pop" when the amplifier is first turned on. A "gas arc" will often damage diode D117 on the
negative rail of the filter capacitor bank and open the fuses in the amplifier. If this problem
occurs frequently, the tube should be tested or replaced. The use of low quality tubes, tubes that
have been stored for extended periods, or abused tubes increase likelihood of a "gas arc".
Ameritron recommends using only current code date 572B tubes.
EXPORT MODIFICATIONS
A simple modification will allow operation on frequencies above 15 meters. Instructions for this
modification are available by sending a written request for "Export Modification Instructions"
along with a copy of a valid amateur license. There is no charge for this information. Export
models are shipped with this modification installed and have an "X" or "Y" following the serial
number.
Address: Ameritron
116 Willow Road
Starkville, MS 39759
FAX:
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(662) 323-6551
Ameritron AL-572
Instruction Manual
TECHNICAL ASSISTANCE
Technical assistance is available during normal central standard time business hours on
weekdays. Customer service is more effective when our technicians are provided the following
information:
1. Model and serial number
2. Date of purchase and dealer
3. An accurate description of the problem
Meter readings at all stages of the tuning procedure are very important along with a complete
description of the other equipment used with our product.
Written assistance is also available. Due to time delays in processing mail, please allow at least
three weeks for a written reply. For service or written correspondence, use the following address:
AMERITRON
116 Willow Rd.
Starkville, MS. 39759
Telephone: (662) 323-8211
FAX: (662) 323-6551
Note: Service history has clearly shown that most problems are operating or installation
errors, rather than equipment failures. Most problems can be resolved over the
telephone. Please contact our staff before shipping parts or equipment to us.
The packing materials used to ship this amplifier were specially designed to prevent shipping
damage. The original packing materials should be used to ship this amplifier. Replacement
packing materials may be purchased from Ameritron if original packing materials are unavailable
or damaged.
CAUTION: Never ship this amplifier with the tube installed.
Ameritron will not be responsible for shipping damage
caused by improper packing.
NOTES
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INSTALLATION GUIDELINES AND SUGGESTIONS
LOCATION OF THE AMPLIFIER
Do not install the amplifier in excessively warm locations or near heating vents or radiators. Be
sure air can circulate freely around and through the amplifier cabinet. Provide an unobstructed
cold air inlet for the amplifier. DO NOT place any books, magazines or equipment that will
impede the free flow of air near or on the cabinet ventilation holes.
VENTILATION
The AL-572 ventilation system has been designed and tested to maintain tube seal temperatures
safely below the tube manufacturer's rating at 600 watts of continuous carrier or 1300 watts of
two tone power output when the amplifier is properly tuned. The fan in the AL-572 is a
permanently lubricated type that requires no maintenance in normal operation. To insure
adequate cooling in your installation, please observe the following:
1. Do not block or unduly restrict the ventilation holes in the cover. Be sure that the amplifier is
located in an area so the ventilation holes have open air circulation. It is particularly important
to avoid restricting the air inlet.
2. The exhaust airflow is over 30 CFM. Do not "assist" the exhaust airflow with cabinet
mounted fans.
3. The most efficient way to improve airflow is to pressurize the air inlet area. Be sure that any
fan used to assist the inlet airflow has at least a 60 CFM rating.
4. The exhaust air will become quite warm at high power levels. Do not place any heat sensitive
objects in the exhaust air stream.
POWER CONNECTIONS
The AL-572 is supplied with a NEMA 5-15P plug for 120 Vac operation. Full duty cycle
operation with ac supply voltages below 100 volts is not recommended. The "TRANSFORMER
CONNECTIONS" section on page 15 show the correct wiring for various supply voltages.
This amplifier has a current demand of 16 amperes at 120 Vac with 1000 watts of RF carrier
output. The average power line current during voice peaks on SSB will be approximately 9
amperes at 1300 watts PEP output. Most normal residential power lines and house-wiring will
easily meet this current requirement.
If the power mains have excessive resistance, the high voltage may sag to less than 2500 volts
under load. Voltage sag will not hurt the amplifier if the fully loaded high voltage remains above
2350 volts.
CAUTION: Never allow the high voltage to exceed 3000 volts under
any condition.
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Ameritron AL-572
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For 120 volt operation, the wiring between the fuse box and the amplifier ac outlet must be
number 14 gauge (or larger) in order to supply the current required (16 A) without a significant
drop in the line voltage. The 120 volt outlet should be fused for 20 amperes.
GROUNDING
Connect a good RF and dc ground to the ground post on the rear panel of the amplifier. Use the
heaviest and shortest connection possible. The best materials to use for ground connections are
(in order of effectiveness) smooth wide copper flashing, copper tubing, or solid copper wire.
Never use braided or woven conductors unless the lead needs to be flexed. Braided or woven
conductors offer a much higher impedance to lightning and RF than an equivalent solid
conductors.
Water pipes, metal heating ducts, metal fences and other large metallic masses offer convenient
RF grounds. If a water pipe ground is used, inspect all the pipe connections to be sure that no
plastic or rubber connections are insulating the pipes. Insulated pipe connections will interrupt
the electrical continuity in the water supply system. Install a jumper around any insulated pipe
connections you find. Use heavy copper wire or flashing with stainless hose or pipe clamps for
the jumpers.
The following tips will help prevent lightning damage and RF grounding problems:
1. Avoid using braided or woven conductors, they have very high resistance for RF and
lightning. Remember that RF and lightning flows along the surface of conductors, almost no
current flows in the center of the conductor. The lowest RF resistance occurs with large
surface area, smooth conductors.
2. Avoid routing a single small gauge conductor along the various pieces of equipment (or to
connect multiple ground sources). Instead, use multiple ground leads that connect to a single
wide buss at the operating position. Keep all ground leads as short and wide as possible.
3. Buried radials provide much better lightning and RF ground connections than ground rods do,
although both are needed for safety.
4. Avoid sharp bends in ground leads. When changing the direction of a ground lead use a
gradual radius turn.
5. Avoid second story operation. A good ground is much easier to obtain on the first floor or in
the basement of a structure.
6. Air-core choke baluns should be used on all coaxial feedlines. The feedlines should be coiled
into several 4" to 6" diameter turns before they enter the building. Either directly bury the
feedlines a few inches deep in the ground for a minimum distance of ten feet or ground the
shields to a separate earth ground on the antenna side of the choke.
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Ameritron AL-572
Instruction Manual
TRANSFORMER CONNECTIONS
The power transformer can be adjusted for various power line voltages by changing a group of
jumper wires located near the outside edge side of the large power supply circuit board. These
jumpers are located above the power transformer and have letters and numbers plainly marked on
the circuit board. The jumper connection points are labeled A through F and 1 through 3.
120 volt operation will normally be adequate in most situations. Operating this amplifier on 240
volts may be advantageous if the 120 volt power mains have abnormally high resistive loss. 240
volt operation is advisable when house lights dim or "blink" during operation or if the amplifier's
HV drops below 2500 volts at full output. For maximum safety, never operate this amplifier on
mains that use fuses or circuit breakers rated above 25 amperes on 120 volts, or 15 amperes
on 240 volts.
The power transformer of the AL-572 has fourteen different voltages available on the primary
and is rated at full power on frequencies of 50 and 60 Hz. The jumper connections chart below
indicates the proper placement of jumpers for various power line voltages.
The high voltage secondary of the AL-572 has three leads. The normal wiring is indicated on the
circuit board silk-screen by the initials R/Y (RED/YELLOW) and R/G (RED/GREEN). For low
power operation the R/Y and R/G wire can be reversed. This will reduce the plate voltage of the
AL-572 to permit operation at output levels below 400 watts.
WARNING:
The AL-572 requires different back panel fuses for
various line voltages.
Use the fuse listed in the
jumper connections chart for maximum protection.
JUMPER FROM TOP LETTERS
TO BOTTOM LETTERS IN COLUMN
HIGHEST
LINE-V
205
215
220
230
240‡
245
250
90
100
110
115
125†
130
140
A
B
C
B
B
B
B
B
B
B
C
C
C
C
C
C
C
A
A
A
A
A
A
A
B
B
B
B
B
B
B
D
D
D
D
D
D
D
†Factory wired Model AL-572 and AL-572Y
‡Factory wired Model AL-572X
16
D
E
F
LINE
FUSE
C
C
C
C
C
C
C
3
3
2
F
1
2
1
3
3
2
F
1
2
1
1
2
1
E
2
3
3
1
2
1
E
2
3
3
12
12
12
10
10
10
8
25
25
25
20
20
20
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Ameritron AL-572
Instruction Manual
INTERCONNECTIONS
1. Connect the exciter's RF output to the "RF IN" connector on the rear of the AL-572 with 50
ohm coax. Use any good quality 50 ohm cable long enough to connect the amplifier to the
exciter. This amplifier connection uses a standard SO-239 female that mates with a PL-259
male connector on the cable.
2. Connect the existing station antenna system to the "RF OUT" connector on the rear of the AL572 with RG-8 type coax. This amplifier connection uses a SO-239 female that mates with a
PL-259 connector on the cable.
3. Shielded audio type cable with a standard male phono plug should be used to connect to the
"RLY" jack on the AL-572. This jack has positive 12 Vdc open circuit and supplies 100 mA
of current when pulled to ground. The relay circuit has an internal back pulse canceling diode
to protect sensitive exciter circuits from damage.
4. Connect a short, wide, and smooth ground lead from a good earth and RF ground to the rear
panel "GND" terminal. Avoid using braided conductors for ground leads.
5. The "12 V" connection on the rear panel provides 12 Vdc at 200 mA maximum to operate
external dial lamps or accessories such as the ATR-15 Antenna Tuner.
6. Connect the "ALC" jack to the ALC input of the exciter with a shielded cable and a phono
plug. The proper connection point on the exciter should be indicated in the exciter's manual.
The AL-572 ALC will operate with any exciter that uses a negative-going ALC voltage of up
to 10 volts.
Note: Transceiver ALC response times and ALC voltage requirements vary with different
manufacturers.
OPERATING INSTRUCTIONS AND GUIDELINES
FRONT PANEL CONTROLS
"MULTIMETER" Switch
This four position switch selects either the plate voltage (HV) of 0-3500 volts, the reflected peak
envelope power (REF) of 0-500 watts, the ALC detector output voltage (ALC) of 0-35 volts, or
the approximate ALC grid current threshold (ALC SET) of 0-350 mA. See the "Metering
Functions" section on page 9 for more details.
"OFF-ON" Switch
This switch turns the main power off and on. When this switch is placed in the "ON" position
the fan should start, the meters should be illuminated, and high voltage should appear.
"STBY-OPR" Switch
This switch disables the amplifier's internal antenna relay. In the "STBY" position the amplifier
is bypassed without turning the tube's filaments or the power supply off.
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This switch will also reset the grid protection circuit if an optional grid overload protection
circuit is installed. The overload circuit will be reset whenever this switch is placed in the
"STBY" position and returned to the "OPR" position.
"PLATE" Control
The "PLATE" control adjusts the output tank circuit to resonance. This control should always be
adjusted for maximum RF output power. Maximum RF output power normally occurs
simultaneously with maximum grid current and very close to the plate current "dip."
"LOAD" Control
This control adjusts the coupling of the amplifier to the antenna or load. This adjustment insures
optimum coupling between the tube and the load as the SWR of the load, the operating
frequency, or the power level is changed. Advancing the "LOAD" control clockwise increases
the RF power output capability and the linearity of the amplifier. Advancing the "LOAD"
control (clockwise rotation) also decreases the grid current and increases the plate current for a
given amount of drive.
The efficiency of the amplifier and the grid current decrease if the "LOAD" control is rotated
beyond the point of maximum output. The linearity, however, will increase. The proper position
for this control is slightly clockwise from the setting that produces maximum output with full
drive power applied to the input. Never use the "LOAD" control to adjust the output power.
Aways set power by reducing exciter power.
The "PLATE" control should always be checked after the "LOAD" control is adjusted by more
than one number. This is especially important at the high end of the "LOAD" range on 20 meters
and above. For example, if the "LOAD" is advanced from 7-1/2 to 8-3/4, the "PLATE" should be
re-tuned. If the "LOAD" is touched up only a slight amount, the "PLATE" setting will not
usually require re-adjustment.
ALC METERING, CONTROLS, AND ADJUSTMENTS
ALC Metering Functions
The "MULTIMETER" switch in the AL-572 has two positions that indicate the functioning of
the ALC circuit. These positions are as follows:
ALC
In this position the multimeter measures the output voltage of the ALC detector. The full scale
reading of the ALC detector voltage is 35 volts. It is read directly from the ALC/ HV scale of the
multimeter. The multimeter will indicate the maximum value of ALC voltage available from the
internal ALC circuit. The meter should flick upwards occasionally during normal ALC action in
this position.
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Ameritron AL-572
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ALC SET
In this position the multimeter measures the approximate grid current that will produce ALC
activity. One zero must be added to the reading on the ALC/ HV scale for this function. For
example: If the meter reads 15, add one zero (150). In this example ALC action will begin at
approximately 150 mA of grid current.
ALC Controls
The position of the "ALC SET" control determines the grid current value that will begin to
produce ALC voltage. Rotating the "ALC SET" control counter-clockwise reduces the
maximum grid current obtainable and the available RF power output. Rotating the "ALC SET"
control clockwise increases the maximum grid current level.
The approximate grid current available before ALC action begins can be determined by placing
the "MULTIMETER" switch in the "ALC SET" (far clockwise) position. The "ALC SET"
control should normally be adjusted to produce a multimeter reading of 12 to 18 volts with the
"MULTIMETER" switch in the "ALC SET" position. This will allow a maximum grid current
of approximately 120 to 180 mA.
ALC Adjustments
SSB Operation
During SSB operation two adjustments affect the ALC and the sound of the signal. One is the
exciter's microphone gain (or RF output level) adjustment. It will control the "fullness" of the
ALC and the average output power. It will have very little effect on the peak output power,
however. The fullness of ALC action is indicated by the meter reading in the multimeter ALC
position. More exciter audio gain or power output will drive the amplifier's ALC circuit harder,
and produce a more constant meter reading. This produces RF compression that increases the
"talk power" without increasing signal bandwidth or distortion.
Note: Audio background noise will increase while using heavy ALC levels on SSB.
Objectionable background noise levels may occur while using heavy amounts of
ALC, especially if the heavy ALC levels are used in conjunction with other speech
processing. In these situations, operating in a quiet room and "close talking" the
microphone will minimize objectionable background noise.
The amplifier's "ALC SET" control determines the level of grid current that produces ALC
activity. The maximum power output level. This amplifier has the best linearity when the "ALC
SET" control is adjusted to limit the peak grid current to 150 mA or lower. This adjustment must
be made with a carrier or single tone signal. When the "ALC SET" control is properly adjusted,
it will be impossible to exceed 150 mA of grid current with any tuning or drive adjustment.
CW Operation
During CW operation the "ALC SET" control voltage should be adjusted just high enough
(clockwise) to allow the desired output power to be reached. The "ALC SET" control should
never be adjusted to the point where the grid current can exceed 200 mA under any tuning or
drive adjustment condition. During proper CW ALC operation, the exciter drive level control
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Ameritron AL-572
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should be adjusted until the ALC voltage meter slightly flickers (ALC position of the
"MULTIMETER" switch) while operating with normal output power levels.
The ALC circuit will limit the amplifier's grid current to a safe value if anything accidentally
changes in the station or the antenna. The CW keying waveform of the radio will remain
unaltered when the ALC is adjusted in this manner.
Note: Caution should be exercised if the ALC SET is used to control the CW power output
with the exciter power control set at maximum. Key clicks may be produced if the
exciter has a poor ALC response time. Check for proper wave shape when using the
ALC in the amplifier exclusively to control the RF output power.
Rear-panel "ALC LIMIT" control
The "ALC Limit" control (rear panel) limits the maximum voltage available from the ALC
circuit. This control is necessary only because the ALC response times and voltage requirements
for exciters have never been standardized. The ALC voltage requirements may even vary
between different models produced by the same manufacturer.
If the ALC response time of the exciter (transceiver) is faster than the rise time of the RF
envelope, there will be no voltage compatibility problems. The ALC voltage from this amplifier
will automatically self-adjust to the value required by the exciter.
If the ALC voltage requirements are low and/or if the ALC attack time is slow, the ALC may
cause the output power to "pump" at a very slow rate. The undesired "pumping" can be corrected
by reducing the amplifier's ALC output voltage with the "ALC Limit" control (R1).
A full counter-clockwise "ALC Limit" setting will produce approximately 10 volts of maximum
negative ALC voltage. A full clockwise setting (viewed from amplifier rear) will produce no
ALC voltage. Always start with this control fully counter-clockwise before slowly advancing
this control clockwise. The "ALC Limit Adjustment" section that follows gives adjustment
details.
ALC Limit Adjustment (rear panel)
This adjustment procedure should be used if "pumping" occurs from excessive transceiver ALC
sensitivity and/or slow transceiver ALC response time:
1. Load the amplifier for maximum output on any band (see tuning instructions later in this
manual).
2. Adjust the "ALC SET" control on the front panel and the rear panel "ALC Limit"
potentiometer to their full counter-clockwise positions.
3. Apply full exciter drive power, and adjust the rear panel "ALC Limit" potentiometer
clockwise (rear view) until the amplifier's ALC output voltage meter (multimeter "ALC"
position) indicates 6 to 10 volts. As an alternative, the potentiometer can be adjusted
clockwise until the RF output power reaches 300-500 watts.
4. Adjust the front panel ALC SET control to the desired power level.
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Ameritron AL-572
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DRIVING POWER
This amplifier is designed to operate at full ratings when it is driven by an exciter that has
approximately 70 watts of RF output. An exciter with a lower output power may be used with a
resulting decrease in amplifier output. Both the driving power and the "LOAD" control must be
carefully adjusted when using an exciter that delivers more than 70 watts. Proper control settings
will help prevent excessive grid current and spurious signals, which create needless interference
to other operators. A monitor scope is recommended for continuous output observation. An
oscilloscope is the best way of determining if the amplifier is "flat-topping" and producing
excessive distortion products.
A second method of determining linear operation is to monitor the peak RF output power
carefully on the AL-572's internal meter. Determine the maximum obtainable RF output power
and reduce the exciter's power until there is a noticeable margin from the maximum output
power. This will insure some reserve power is available for random voice peaks.
Note: Never increase the drive power beyond the point where the amplifier's output power
stops increasing. This is also the point where the grid current will begin rising
rapidly.
The amplifier is being over-driven for a given "LOAD" setting when the grid current increases
rapidly while the plate current and output power increase slowly. The amplifier "LOAD" control
needs to be advanced to a higher number if this condition occurs. Non-linear operation, splatter,
and excessive grid current will occur if the "LOAD" setting is too low. Excessive plate current is
the proper indicator that the drive power limit has been reached.
TUBE AND COMPONENT LIFE
These guidelines will help prolong tube and component life, and minimize splatter.
1. On SSB or other linear modes virtually any amount of power will cause splatter if the loading
is too light ("LOAD" control too far counter-clockwise). Always tune for maximum output
with maximum drive power. Reduce the drive power to reduce the output power on SSB, not
the loading control.
2. Lightly loading an amplifier will also result in large voltages building up in the tank circuit.
Under-loading an amplifier is much harder on the tubes and other components than operating
a properly loaded amplifier into a high SWR or with excessive drive power. We recommend
slightly overcoupling the amplifier (loading control advanced slightly beyond the point of
maximum output) to insure the best linearity and freedom from arcing.
3. Never depend on average reading power or current meters to indicate proper operation on
SSB or other linear modes. The best indicator of linearity is either an oscilloscope or the
internal PEP RF output meter. Maximum linearity can be determined by finding the
maximum output power possible and then reducing the exciter power for a slight reduction in
output power.
4. Never exceed 170 mA of grid current on CW carrier during actual operation. The proper grid
current for SSB will range from 0 to 75 mA. The SSB grid current will vary with the
operator's voice, the amount of signal compression or processing, and the tube characteristics.
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Ameritron AL-572
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TUNING
WARNING:
The transformer must be wired correctly for your line
voltage. This amplifier is normally shipped wired for
standard 120 Vac operation.
See the "TRANSFORMER
CONNECTIONS" section on page 15 for details.
Important Note: If you have installed the optional electronic grid protection circuit to
prevent control-grid damage, this amplifier will quit operating if the grid
current exceeds a safe pre-set limit. The overload circuit responds much
faster than the grid current meter. The overload circuit will respond to
excessive grid current before the operator can observe the increase on the
grid current meter. The grid overload circuit can be reset by momentarily
placing the "STBY-OPR" switch in the "STBY" position.
Many exciters generate high-level RF pulses when first keyed. These short duration pulses may
greatly exceed the exciter's operating output power setting. Unexplained activation of the grid
overload circuit may indicate the existence of this common exciter problem.
Never under-load the amplifier to reduce the output power. The amplifier "LOAD" control must
be set to a high enough position (clockwise) to prevent excessive voltage and arcing in the tank
circuit or excessive grid current. Repeated tripping of the grid overload circuit or intermittent
arcing probably indicates the "LOAD" control is adjusted too low.
The goal of the following tuning procedure is to adjust the amplifier tuning and loading to
provide maximum output at maximum exciter power. Avoid depending on the exciter's power
control or ALC to maintain reduced power output, and peaking the amplifier at this reduced drive
level. If the exciter suddenly puts out more power, the sudden surge of energy can cause splatter
or cause the amplifier to arc.
Overshoot is especially troublesome with radios capable of operating at more than 100 watts
output power. For example, in several tests of popular 150 watt output radios, several radios
adjusted to provide less than 100 watts output power during carrier conditions "spiked" above
200 watts before their ALC systems took control. The transcient output power pulse is fast, often
lasting only a few milliseconds. The rapid speed of the pulse prevents normal peak reading
meters or non-storage oscilloscopes from clearly indicating the problem.
Overshoot problems are common, and we recommend slightly over-coupling the amplifier to the
load. Overcoupling is accompished by advancing the LOAD control slightly beyond the point of
maximum output power with full exciter drive (not to exceed 110 watts).
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Ameritron AL-572
Instruction Manual
Tuning Procedure
Proper tuning will produce excellent output power, a clean signal, and good tube life. If the
various meter readings are different than indicated in the text, check the external amplifier
connections. Consult the manual for the exciter if necessary.
Please go through the following procedure carefully, in numerical order, until you develop a
"feel" for operating and tuning this power amplifier. Once you are used to operating this
amplifier, steps not marked with an asterisk (*) can be eliminated.
1. Set the AL-572 front panel switches as follows:
POWER
OPR-STBY
MULTIMETER
to
to
to
OFF
STBY
HV
2. Plug the ac line cord into the proper voltage outlet.
*3. Place the main power switch in the "ON" position. The meter lamps should light and the
blower should start. Read the 3500 volt scale on the multimeter. It should indicate 2800
volts nominal and no more than 3000 volts.
4. With the amplifier still on "STBY", tune the exciter into a normal 50 ohm load according to
the manufacturer's instructions (solid state radios do not normally require this adjustment).
Turn the exciter drive down after tuning.
*5. Place the amplifier's "BAND" switch on the same band as the exciter. Set the "PLATE"
control and the "LOAD" control as indicated below:
CW
Frequency
1.810
3.600
7.050
10.125
14.050
18.125
21.050
24.900
28.050
PLATE
3-1/2
2
6-1/2
4-1/2
8-1/2
8
9
8-1/4
9-1/2
LOAD
3-1/2
1-1/2
1
0
4
2-1/4
5-1/2
3
5-3/4
PHONE (SSB)
Frequency
1.850
3.900
7.200
14.250
21.350
28.500
PLATE
4
3-1/4
7
8-1/2
9-1/4
10
LOAD
4-1/2
3-1/4
2
4
6
6
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Ameritron AL-572
Instruction Manual
6. With the exciter's drive level still on zero, observe the 1000 mA Ip scale on the left hand
meter. It should indicate zero (0) amperes.
*7. Place the "STBY-OPR" switch in the "OPR" position. Place the exciter in the transmit
mode with no RF output. The red "XMT" LED should light and plate current (Ip on the left
meter) should be close to zero (0).
8. With the exciter in the transmit mode, apply a very low amount of RF drive power (about
100 mW). The plate current meter (Ip) should suddenly indicate about 100 mA.
Note: Currents may vary up to 25% due to component and line voltage tolerances. If the
current in this step is higher than expected, the RF level from the exciter may be too
high.
If the exciter does not allow adjustment to very low CW power levels, the exciter can be
placed in the SSB mode and the audio (microphone) gain control advanced from minimum
while speaking until the plate current (Ip) just flickers upwards. The plate current (Ip)
should be around 100 mA on these flickers.
9. Place the "MULTIMETER" switch in the "ALC SET" position. Adjust the front panel
"ALC SET" control until the multimeter indicates 8 volts. This adjustment will limit the
amplifier's grid current to approximately 80 mA.
Steps 10a and 11a require a connection from the amplifier's ALC output to the exciter's ALC
input.
Steps 10b and 11b should be used if the exciter and amplifier ALC lines are not connected.
Note: Step 10 requires the simultaneous observation of the plate current (Ip) and the grid
current (Ig).
10a. If the ALC line is connected, adjust the exciter's drive or power output control to
maximum. NEVER ALLOW THE GRID CURRENT (Ig) TO EXCEED 120 mA OR THE
PLATE CURRENT (Ip) TO EXCEED 500 MILLIAMPERES AT THIS STAGE OF TUNING.
If either current exceeds these limits, reduce the exciter's power. Adjust the "PLATE"
control for maximum output power. The plate current (Ip) of the amplifier and the output
power of the exciter should dip (decrease) when this adjustment is made.
10b. If the ALC is not connected, place the exciter in the transmit mode and gradually increase
the drive until a grid current of 120 mA or a plate current of 600 milliamperes (whichever
is higher) appears. The "PLATE" control should be adjusted until maximum grid current
and maximum RF output power appear. The plate current (Ip) should dip slightly when the
grid current and output power peak.
Remove drive power and unkey exciter.
*11a. Increase the "ALC SET" voltage (if the ALC is connected) until 180 mA (18 volts) is
indicated. Apply full drive (not to exceed 100 watts) and adjust the "LOAD" and "PLATE"
controls for maximum RF output power. The grid current should not be allowed to go
above 200 mA at this stage. The plate current should not be allowed to exceed 750 mA
except during brief periods of tuning (15 seconds).
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Ameritron AL-572
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*11b. Increase the exciter drive power (if the ALC is not connected) until 180 mA of grid current
is indicated. Adjust the "LOAD" and "PLATE" controls for maximum RF output power.
The grid current should not be allowed to go above 200 mA at this stage. The plate current
should not be allowed to exceed 750 milliamperes except during brief periods (15 seconds
or less).
*12a. For CW operation, the output power should be reduced with the "ALC SET" control until
the rated output power of 1000 watts is obtained. The exciter's power can be reduced until
the multimeter shows a slight upward flicker with the "MULTIMETER" switch in the ALC
position if the ALC is used.
*12b. For SSB operation, the "ALC SET" should be adjusted to allow 120 mA of grid current
(near the 12 volt marking). The exciter should be set to produce maximum output power
(not to exceed 110 watts of peak power). Next the amplifier's "LOAD" and "PLATE"
controls are adjusted for maximum power output on the internal peak reading RF wattmeter
with either a two-tone generator or sustained "HEL-L-L-L-L-O" driving the exciter.
The "ALC SET" control should then be reduced until the peak power output is just reduced
slightly. Finally the exciter's audio gain or output power is adjusted until the multimeter
"ALC" position indicates the desired ALC level. This setting should normally allow around
120 mA grid current on a steady carrier or "whistle".
Note: If the ALC is not connected, the amplifier should be fully loaded with maximum
drive (not to exceed 110 watts). The exciter's output should then be reduced (either
with the microphone gain or power output control until the output power shows a
very slight reduction.
"ALC SET" control
Proper adjustment of the front panel "ALC SET" control accomplishes the following:
1. The exciter's power is limited to a value that will produce a fixed amount of grid current in
the amplifier. The front panel "ALC SET" control determines the maximum grid current
that can be produced.
2. The "LOAD" control setting will determine the maximum plate current and output power
for a given grid current. Never exceed 750 mA of long duty cycle (more than 15 seconds
without a 15 second cool down period) plate current. Never exceed 200 mA of operating
grid current.
3. For normal SSB operation, the exciter power should be reduced until the ALC voltage
(measured in the ALC multimeter position) flicks upwards on occasional voice peaks. This
will produce the best audio quality. The drive can be increased for DX or weak signal SSB
operation until the ALC steadily registers voltage.
Also see the "ALC METERING, CONTROLS, AND ADJUSTMENTS" section beginning on page 17,
and the "MULTIMETER" section beginning on page 9.
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Ameritron AL-572
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ADDITIONAL SSB NOTES
The peak power output developed on SSB is limited by the amplifier loading, RF drive, and
peak-to-average power of the RF waveform. Proper loading of this amplifier will produce
excellent linearity and a clean signal even if the output power level exceeds one kilowatt PEP.
An improperly adjusted (too far counter-clockwise) "LOAD" adjustment can produce flattopping and splatter with only a few hundred watts of RF output. The "LOAD" setting is the
single most important adjustment for proper SSB operation.
Note: Always remember that the "LOAD" control setting is much more important than
any other parameter for good linearity! Good linearity means a "clean" signal!
To maintain linearity, always be sure that the "LOAD" control is adjusted slightly further
clockwise than the position that gives maximum output at peak or maximum drive.
Be considerate of others, NEVER "push" this amplifier into envelope clipping or to the point
where the grid current approaches 75 mA on voice peaks. Envelope clipping can be also be
avoided by adjusting the amplifier's "ALC SET" control until the peak output power drops
slightly from the power obtained with full microphone gain and a fully clockwise /"ALC SET"
adjustment. For the cleanest audio, the microphone gain can be reduced until the ALC meter just
flickers.
AM (AMPLITUDE MODULATION) OPERATION
The efficiency of any conventional linear amplifier must remain below half the peak efficiency
under maximum signal conditions (less a safety factor) in AM operation. Since this linear
amplifier has a peak plate efficiency of nearly 60%, the carrier efficiency must be kept below
30% to maintain linearity. The power dissipated in the tube anodes will slightly more than twice
the carrier output power.
The carrier power must be kept below 250 watts for clean and safe AM operation. With 250
watts of carrier, the peak envelope power will reach 1000 watts with 100% symmetrical
modulation. The modulated AM power output should be limited to 1300 watts peak with nonsymmetrical modulation that enhances the positive peaks.
AUDIO DISTORTION
One problem that often occurs when using a linear power amplifier is SSB audio distortion on
one or more bands. This distortion is usually caused by RF feedback from either a poorly
designed antenna or poor RF grounding. REMEMBER THAT A GOOD GROUND FOR DC IS
NOT NECESSARILY GOOD FOR RF. RF circuits require short connections with smooth, wide
conductors. Braiding or woven wire has a very high RF resistance and should be avoided. See
the "GROUNDING" section on page 14 of this manual. More detailed suggestions on grounding
are available by requesting Ameritron's Tech Bulletin on RF Feedback.
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Ameritron AL-572
Instruction Manual
FM (FREQUENCY MODULATION), RTTY, AND DIGITAL OPERATION
The efficiency of this amplifier will approach 62% in the FM, RTTY and DIGITAL
OPERATION modes. Since these modes do not require linear amplification of complex
waveforms, the tuning can be re-adjusted for maximum power at the desired output power level.
This will keep the efficiency as high as possible.
QSK OPERATION
The antenna transfer relay in the AL-572 takes approximately 15 milliseconds to change states.
This precludes using the standard internal relay for QSK CW operation. Commonly available
vacuum relays are specified at 5 to 7 milliseconds of switching time. Even expensive vacuum
relays are less than ideal for high speed QSK operation. At 60 WPM, less than 50% of the
receive-time is available with vacuum relays.
On PACKET, AMTOR, and other modes, delay can be added to the transmit and receive
changeover to use either vacuum or our standard relay effectively. Ameritron offers two highspeed PIN diode options that permit operation on modes requiring high speed receive-transmit
switching. Both systems offer noiseless switching times of under one millisecond. Since these
PIN diode systems are several times faster than vacuum relay systems, they will allow over 90%
of the available receive time to be used at 60 WPM.
Ameritron highly recommends using the external QSK-5 switch. This stand alone PIN diode
switch can be used with almost all types of amplifiers and transmitters. Modifications are not
required in amplifiers used with the QSK-5 unit. The QSK-5 operates directly from 120 Vac
power lines.
Ameritron also offers an internal QSK board as a space-saver for the AL-572. This internal
board is slightly less expensive. However, it provides less flexibility and serviceability than the
external QSK-5 unit. Factory installation of the QSK-5PC is highly recommend. Contact
Ameritron for details on the QSK-5 and the QSK-5PC.
PERIODIC MAINTENANCE
The high voltage present on various parts of the amplifier will attract dust and dirt. The high
voltage areas at the bottom of the plate choke and the plates and insulators of the air variable
capacitors should be kept dust free. These areas should be inspected periodically, especially if
the amplifier is operated in a dusty environment. These areas may be inspected by unplugging
the line cord and waiting a few minutes for the power supply capacitors to discharge. The high
voltage should then be checked with the internal multimeter by placing the meter switch in the
HV position.
DANGER:
High voltages can kill!
Accidental contact with the
voltages in this amplifier can be lethal!
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Ameritron AL-572
Instruction Manual
For your personal safety please observe the following precautions:
1. NEVER defeat the interlock.
2. NEVER remove the cover with the amplifier connected to the power line.
3. ALWAYS allow the capacitors to discharge for several minutes after unplugging the
amplifier and before removing the cover.
4. ALWAYS select the high-voltage (HV) function of the Multimeter to check the high voltage
potential. Do not remove the cover if voltage is indicated.
5. ALWAYS ground the tube anode (top metal conductor) to the chassis before touching
anything inside the amplifier.
6. ALWAYS be cautious of heat. Many components inside the amplifier operate at high
temperatures.
7. NEVER make any unauthorized component or circuit modifications to this product. The only
acceptable source for modifications is Ameritron or a source approved by Ameritron.
Unauthorized modifications almost certainly will increase the risk of equipment failure or
personal injury.
The cover should be removed and a low value (40 to 500 ohm) two-watt or larger resistor should
be secured to the chassis. The other end of this resistor should be connected to the tube anode
with an insulated clip lead.
CAUTION: NEVER ground the anode directly to the chassis without
a series resistor. Component damage may occur from the
current surge.
Note: This resistor is a safety device that must be installed when beginning service work
and removed when the work is finished.
Dust and dirt can be blown out of the amplifier with a shop vacuum or a high pressure air hose.
A soft bristle brush dipped in alcohol can be used to clean particularly dirty areas. If the amplifier
is operated in a dusty environment, a non-conductive low- restriction foam air filter can be
placed over the ventilation holes on the left side of the cabinet near the filter capacitors. Placing
an air filter over these air inlet holes will substantially reduce the amount of dust entering the
cabinet. Most hardware stores stock suitable air filter material that are used as replacement filters
for window air conditioners.
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Ameritron AL-572
Instruction Manual
PARTS LIST
POWER SUPPLY / SWR BOARD (50-0057-1)
Designator
D101,102,114,115
D103
D116-120
D104-113
C101
C102,105
C103
C104
C106,125,126,129,135-137
C140
C107-116
C117-124
C127
C128,138,132,139
C130,131
C133
C134
R101
R102
R103,104,121
R105
R106
R107
R108,109
R110,111
R112-119
R120
R122
R123
R124,125
R126,128,128
R127
R130
RLY101
RLY102
RFC101
T101
Q101
Q102
Q3 (see main chassis)
F101
Description
1N34A
1N757A Zener 9.1V
1N4001
1N5408
27 pF 500 V
.001 uF 1 kV
10 pF 1 kV
3-12 pF 500 V Trim
.01uF 50 V Disc
.47 uF
.01 uF 1 kV
210 uF 450 V Elect.
270 pF 500 V
.1 uF 50 V
.01 uF 250 Vac
2200 uF 25 V
220 uF 25 V
4.7k mox 1 W
470k 1/4 W
10k 1/4 W
10 ohm 1/2 W
1.5 ohm 2 W 1%
0.6 ohm 3 W 1%
1M 3 W 1% special high voltage type
750k 2 W mox 2%
50k 7 W 5%
51ohm 2 W mox 5%
6.8k 1/4 W
1.8k 1/4 W
50k trim pot
47k 1/2 W
10 ohm 10 W
47 ohm 1/2 watt
3PDT 12 Vdc
SPST 12 Vdc
Choke 3 turns FB-73
Toroid
2N3904
2N3906
MJF3055 transistor, NPN
2A
Ameritron P/N
300-0346
305-0757
300-0266
300-0145
208-5404
200-2120
200-3531
204-0150
200-0416
203-0530
200-2121
203-0578
208-5775
200-0754
200-2122
203-0207
203-0565
103-1747
100-0188
100-4100
100-0727
103-3400
103-3399
103-2223
103-1743
103-7580
103-2151
103-1747
100-0728
104-0400
101-0402
103-9702
101-1470
408-6140
408-6148
10-15168
10-14134
305-0645
305-0722
305-3055
755-1102
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Ameritron AL-572
Instruction Manual
TUNED INPUT BOARD (50-0057-2)
Designator
C201 (transmitter side)
C202 (tube side)
C213-215
RFC1
L201
S201
Description
See input chart
See input chart
.01 1 kV disc capacitor
filament choke 30 ampere
See input chart
Input switch
Ameritron P/N
AL-572 TUNED INPUT CHART
BAND
160
80
40
20/30
15/17
10/12
C217
C201,211 (pF) input
2700
(208-5689)
1300
(208-5177)
750
330
270
100
23.75T
22.75T
13.75T
9.75T
8.75T
3.75T
68 pF
L201
new
new
(405-1137)
(405-1097)
(405-1087)
(405-1037)
C 202,212(pF) tube
2700
(208-5689)
1000
(208-5176)
500
(208-5691)
220
(208-5175)
180
(208-5396)
METER BOARD (50-0057-3)
Designator
D301
C301, 302
C303, 304, 307-311, 314, 315
C305, 306
R301, 302
R303
R304
R305
R306, 310
R307
R308, 311
R309
R312
R313
IC301
Q301, 302
Q303
S301
30
Description
1N34A
.47 uF 50 V tantalum
.1 uF 50 V
.001 uF 1 kV
2.2M 1/4 W
390 ohm 1/4 W
2.2k 1/4 W
470k 1/4 W
10k 1/4 W
100 ohm 1/4 W
33k 1/4 W
4.7k 1/4 W
330 ohm 1/4 W
270 ohm 1/4 W
LM324
2N3904
2N3906
Rotary 2P6T
Ameritron PN
300-0346
203-0530
200-0754
200-2120
100-6220
100-0390
100-1500
100-0188
100-4100
100-2100
100-3330
100-1470
100-0330
100-0600
311-0324
305-0645
305-0722
500-0563
Ameritron AL-572
Instruction Manual
TIMER / OVERLOAD BOARD (50-0057-5)
Designator
C501-506
C507,508
C509
D501, 502
D503
IC501
Q501
Q502
Q503, 504
R501-503
R504, 505
R506, 508
R507
R509
R510
R511
RLY501
FB
Description
.01 uF 50 V disc
.47 uF tantalum
100 uF 25 V
1N4001
5.6 V zener
LM 358 dual op-amp
NPN transistor MJF3055
PNP transistor 2N3906
NPN transistor 2N3904
10k 1/2 W
3.3k 1/4 W
680 ohm 1/4 W
1.8k 1/4 W
1 meg 1/4 W
1k 1/4 W
180 ohm 1/2 W
DPDT 12 V dip relay
FB 73-801 Ferrite Bead
Ameritron P/N
200-0416
203-0530
203-0564
300-0266
301-710
311-0724
305-3055
307-0722
305-0645
101-0643
100-0729
100-0532
100-0728
100-0730
100-0727
101-0384
408-2135
10-15168
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Ameritron AL-572
Instruction Manual
AL-572 MAIN CHASSIS PARTS LIST
Designation
B1
C1-3
C4
C5, 6
C7
C8
C11-13
C14-19
D1
F1, 2
50-0080-1
50-0080-2
50-0080-3
50-0080-4
50-0080-5
L1
L2
L3
M1
M2
R1
R2
R3-4
PC1-4
RFC2
RFC3
S1
S2
S3
S4
R16
Q3
T1
V1-4
32
Description
Fan
.001 uF 7.5 kV
500 pF Doorknob 7.5 kV
170 pF Doorknob 7.5 kV
Air Variable Plate 250 pF 3.5kV
Air Variable Load 800 pF 1.2 kV
.01 uF 50 volt dc disc capacitor
.01 uF 1kV disc capacitor
LED, Red
See Jumper Connections Chart
Power Supply / SWR Board Assembly
Input Circuit Board Assembly
Metering Board Assembly
RF Tank Board Assembly (only parts L1-L2)
Timer-Overload Board Assembly (optional.-See page 31)
"L " Coil
LF Coil (mounted on 50-0572-4)
HF Coil (mounted on 50-0572-4)
Meter (Forward and Reflected)
Meter (grid and plate)
1 k pot (ALC limit)
100 k pot (ALC SET)
51 ohm 2 watt carbon composition
Parasitic choke assembly
Plate Choke
2.5 mH Choke
Band Switch
Lighted Switch
Rocker Switch
Interlock Switch
33 ohm 1/4 watt
Transistor MJF-3055
Transformer
572B Tube
Ameritron P/N
410-3138
200-7224
210-0470
209-0559
204-2112
204-2573-1
200-0416
200-2121
320-0522-1
-------------50-0572-1
50-0572-2
50-0572-3
50-0572-4
50-0572-5
10-13165
10-13240
10-13108
400-3581
400-3580
105-1301
105-1341
10-00572
10-15197
402-1162
500-2135
507-1157
507-1150
504-3247
100-1330
305-3055
406-0572-1
350-0572