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AL-572
Service manual
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Ameritron AL-572 Service 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
Notes................................................................................................................................12
Location Of The Amplifier..............................................................................................13
Ventilation........................................................................................................................13
Power Connections ..........................................................................................................13
Grounding........................................................................................................................14
Transformer Connections.................................................................................................15
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Ameritron AL-572 Instruction Manual
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
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
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:DANGER: NEVER APPLY POWER TO THIS AMPLIFIER WITH THE COVERNEVER APPLY POWER TO THIS AMPLIFIER WITH THE COVER
REMOVED! CONTACT WITH THE VOLTAGES INSIDE THISREMOVED! CONTACT WITH THE VOLTAGES INSIDE THIS AMPLIFIER CAN BE FATAL!AMPLIFIER CAN BE FATAL!
PLEASE READ THIS MANUAL BEFORE ATTEMPTING TO OPERATE EQUIPMENT!
WARNING:WARNING: Improper or abusive operation of this amplifier can damageImproper or abusive operation of this amplifier can damage
the tubes the tubes or other components in this amplifier. Damageor other components in this amplifier. Damage
caused by improper or abusive caused by improper or abusive operation is operation is not not coveredcovered
under the warranty policy.under the warranty policy.
Ameritron 116 Willow Road Starkville, MS 39759 (601) 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:DANGER: Never remove the cover while this amplifier is connected toNever remove the cover while this amplifier is connected to
the power mains! Contact with the voltages in this amplifierthe power mains! Contact with the voltages in this amplifier can be fatal.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:CAUTION: Always use fast-blow fusesAlways use fast-blow fuses rated at 250 volts or higher. rated at 250 volts or higher.
NEVER use standard automotive glass fuses or slow-blowNEVER use standard automotive glass fuses or slow-blow fuses.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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Ameritron AL-572 Instruction Manual
FEATURES
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The AL-572 uses rugged inexpensive 572B tubes.
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The 572B requires only a few seconds of warm-up time.
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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.
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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.
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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.
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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.
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Filament and plate voltages are maintained using the "STBY/OPR" switch. This allows the amplifier to be conveniently bypassed for "barefoot" operation.
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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.
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An "XMT" LED on the front panel indicates proper keying of the amplifier by the exciter.
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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.
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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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Ameritron AL-572 Instruction Manual
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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Ameritron AL-572 Instruction Manual
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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Ameritron AL-572 Instruction Manual
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:DANGER: High voltage can kill! Accidental contact with the voltagesHigh voltage can kill! Accidental contact with the voltages
in this amplifier can be lethal.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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Ameritron AL-572 Instruction Manual
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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Ameritron AL-572 Instruction Manual
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.
WARNING:WARNING: NEVER drive this amplifier with more than 100 watts ofNEVER drive this amplifier with more than 100 watts of
short term average envelope power. NEVER allow the gridshort term average envelope power. NEVER allow the grid current to exceed 200 mA under any operating condition.current to exceed 200 mA under any operating condition.
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