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AL-800
Instruction Manual
TABLE OF CONTENTS
Unpacking Instructions ....................................................................................................1
Features............................................................................................................................3
AL-800 Technical Specifications ....................................................................................4
General Information.........................................................................................................6
Safety Interlock....................................................................................................6
ALC .....................................................................................................................6
Dynamic Bias.......................................................................................................7
Timer - Overload Circuits................................................................................................7
Grid Overload Protection.....................................................................................7
Thermal Overload................................................................................................8
Cathode Warm-up Timer.....................................................................................8
Power Supply...................................................................................................................8
Heater Supply ......................................................................................................8
Plate (HV) Supply................................................................................................8
Meters ..............................................................................................................................9
Current Meter (plate and grid):............................................................................9
Multimeter ...........................................................................................................9
Multimeter Functions ..........................................................................................9
Wattmeter Circuit ................................................................................................10
Peak Envelope Power vs. Average Power ...........................................................10
Tube Life .........................................................................................................................10
Export Modifications.......................................................................................................12
Technical Assistance .......................................................................................................12
Installation Guidelines and Suggestions ..........................................................................13
Location Of The Amplifier .................................................................................13
Ventilation ...........................................................................................................13
Power Connections ..............................................................................................13
Grounding............................................................................................................14
Transformer Connections ................................................................................................15
Jumper Connections.............................................. ..........................................................15
Interconnections...............................................................................................................15
Operating Instructions And Guidelines ...........................................................................16
Front Panel Controls ............................................................................................16
Driving Power......................................................................................................17
Tube and Component Life ...................................................................................18
Additional SSB Notes..........................................................................................18
AM (Amplitude Modulation) Operation .............................................................19
Audio Distortion ..................................................................................................19
FM (Frequency Modulation), RTTY, and DIGITAL OPERATION...................19
ALC Metering, Controls, and Adjustments .....................................................................19
ALC Metering Functions .....................................................................................19
ALC Controls.......................................................................................................20
ALC Adjustments ................................................................................................20
Rear-panel "ALC LIMIT" control .......................................................................21
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ALC Limit Adjustment (rear panel) ....................................................................21
"ALC SET" control..............................................................................................22
Tuning..............................................................................................................................22
QSK Operation ................................................................................................................25
Periodic Maintenance ......................................................................................................26
Parts List ..........................................................................................................................27
Timer / Overload Board (50-0117-2)...................................................................27
Power Supply / SWR Board (50-0800-1) ............................................................28
Meter Board (50-0800-3).....................................................................................29
Tuned Input Board (50-0800-2)...........................................................................29
AL-800 Tuned Input Chart ..................................................................................29
AL-800 Main Chassis Parts List..........................................................................30
Frequency Coverage ........................................................................................................31
Amplifier Tuning Log......................................................................................................31
Notes:...................................................................................................................31
Schematics .......................................................................................................................32
Power Supply / SWR Board ................................................................................32
Tuned Input Board ...............................................................................................33
Meter Board .........................................................................................................34
Timer / Overload Board.......................................................................................35
Main Chassis........................................................................................................36
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Instruction Manual
Ameritron AL-800
1200 Watt Linear Amplifier Instruction Manual
The Ameritron AL-800 is a 1200 watt PEP output linear amplifier that operates from 160 through
15 meters. The AL-800X and AL-800Y are export models that operate from 160 through 10 meters.
Export modification instructions are only available with proof of a valid amateur radio license.
The AL-800 uses a single 3CX800A7 tube 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, electronic grid current and thermal overload protection, and
automatic bias switching to make this the best featured and most reliable single 3CX800A7
amplifier available. The AL-800 and AL-800Y are factory-wired for 120 volt, 50/60 Hz ac line
voltage. The AL-800X is factory wired for 240 volt, 50/60 Hz ac line voltage. All models are
easily converted to other supply voltages between 90 and 250 volts ac.
WARNING:
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!
Improper or abusive operation of this amplifier can damage the tube or other components in
this amplifier. Damage caused by improper or abusive operation is not covered under the
warranty policy.
Unpacking Instructions
Remove the 3CX800A7 tube from its shipping carton. Carefully unwrap the tube and inspect it for
visible damage. Look for a dented anode cooler and broken or bent pins. Roll the tube over slowly
and listen 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-800 is
shipped with the rubber chimney, fuses and fuse caps packed inside the amplifier. Additional
screws will be included in the fuse pack if they are required.
WARNING:
Never remove the cover while this amplifier is connected to the power mains!
Contact with the voltages in this amplifier can be fatal.
The tube must be installed in its socket prior to operation. Observe the pin configuration on the tube
and the socket. Two of the pins are separated by a large space. Carefully observe the pin alignment
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to be sure the tube pins are centered on the socket's metal contacts. Firmly press the tube into its
socket. Do NOT twist or force the tube into the socket.
Install the rubber chimneys over the tube. The seam of the chimney must face the fiber panel. The
bottom of the chimney has notches that must fit over the grid connectors near the base of the tube.
The heavy copper strap anode lead connects to the spacer on the center panel with the 6-32 screw
and nut provided. Install the anode spring clip connector on the tube's anode cap.
The top cover should now be installed with the vent holes on side of the cover positioned near the
electrolytics. The vent 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.
Install the fuses and fuse caps on the back of the amplifier. This amplifier uses two 20A fuses for
standard 120 Vac operation. If you wish to operate the amplifier on a line voltage other than 120 V,
the jumpers on the power transformer primary windings must be changed. If the line voltage 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 fuses or slow-blow fuses.
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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Features
1.
The AL-800 uses a rugged high-gain 3CX800A7 tube.
2.
A time-delay circuit provides a 180 second warm-up to eliminate potential damage to the tube
cathode.
3.
A grid overload circuit quickly disables the amplifier if the grid current becomes excessive.
This feature prevents excessive grid current from causing distortion or damaging the tube or
other components.
4.
A thermal overload automatically disables the amplifier if excessive heating of the power
transformer occurs.
5.
A dynamic bias circuit eliminates hundreds of watts of unnecessary heat generation in the
power amplifier tube. The result is cooler operation and longer component life.
6.
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.
7.
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.
8.
The AL-800 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.
9.
Heater and plate voltages are maintained using the "STBY/OPR" switch. This allows the
amplifier to be conveniently bypassed for "barefoot" operation.
10. 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.
11. "XMT" and "OL" LED's on the front panel indicate proper operation of the amplifier.
12. A rear panel 12 Volt auxiliary output jack provides up to 200 mA at 12 Vdc for accessories
such as the ATR-15 Antenna Tuner.
13. A step-start circuit limits the inrush current to the power supply and tube heater. This circuit
extends the life of the amplifier components.
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AL-800 Technical Specifications*
Input:
Circuit type:
Maximum VSWR at resonance:
Minimum 2:1 VSWR bandwidth:
Maximum drive power permissible:
Typical drive for full power output:
Pi-network, slug tuned coils
1.3:1 or less
20% of center frequency
100 watts PEP
85 watts
Output:
Circuit type:
Typical SSB PEP voice operation:
CW continuous operation:
1/2 hour PEP two-tone test:
1/2 hour continuous carrier (RTTY):
Frequency Coverage:
Third Order IMD:
Pi-L, Pi-network
1200 + watts
850 watts
1200 watts
700 watts
1.8 to 21 MHz amateur Bands. (Export models
include 24.5 and 28 MHz)
-35 dB or better (at rated output)
Efficiency:
CW:
SSB:
approximately 65%
approximately 65% (envelope crest)
Power Supply:
Circuit type:
No load voltage:
Full load voltage:
Full load current:
Regulation:
Transformer:
Capacitors:
Normal line current at rated CW output:
Normal line current at 1200 watt PEP output:
Power line current in standby:
Full wave voltage doubler
2600 V
2250 V
1.2 A
12%
32 lb. E-I lamination grain oriented
63 mFd total, computer grade
16A at 120 Vac
17 A at 120 Vac
0.9 A at 120 Vac
Tube:
Type:
Continuous dissipation:
Warm-up time:
Estimated life:
3CX800A7
800 watts total
180 seconds
8,000 hours ICAS
* Exact performance measurements may vary due to the accuracy of test equipment and the measurement methods
used. (Prices and specifications subject to change without notices.)
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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:
Line:
Others:
SO-239
NEMA 5-15P, standard 120 V three wire
RCA Phono
Physical:
Dimensions: 14-1/2"D x 14-1/4"W x 8-1/2"H
Weight:
68 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 allows ac line
voltage to reach the power transformer. The interlock will open and remove line voltage from the
transformer primary if the top cover is removed.
WARNING:
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 (outer metal surface) 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.
ALC
The AL-800 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. The 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 50-0800H-3 (behind the
"MULTIMETER" switch). IC301 (pin 9) samples 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 (pin 10).
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Pin 8 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.
Dynamic Bias
Conventional bias circuits allow 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-800 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-800 has a full resting period of very
low dissipation between dots and dashes on CW and between words on SSB. The lower idling
current dramatically reduces component temperatures 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's conduction angle is never reduced below class
AB.
The dynamic bias circuit is located on the Power Supply Board P/N 50-0800-H1. 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 voltage of D103,
Q103 will move towards cut-off and the collector voltage will increase. Q103 is, in effect, a current
buffer for zener diode D103.
Timer - Overload Circuits
CAUTION:
Never modify or disable protection circuits without factory approval. Doing so
with void all manufacturer's warranties.
Grid Overload Protection
This amplifier contains a fast acting electronic grid protection circuit to enhance tube life. The
amplifier will quit operating and the "OL" and "XMT" LEDs will both illuminate if the safe limit
of grid dissipation is approached or exceeded. The grid overload protection circuit is reset whenever
the "STBY-OPR" switch is placed in the "STBY" position.
Note:
7
This circuit has a much faster response time than the grid meter. This circuit also
measures the peak grid current. The operator may not observe the grid current
meter climbing before the overload circuit responds and disables the amplifier.
AL-800
Instruction Manual
This circuit is located on the Timer / Overload board P/N 50-0800-5. IC501 (pin 5) senses the
voltage across the grid shunt (power supply board, R106) through terminal 1. If the voltage at pin 5
exceeds the regulated voltage at the junction of R505 and R511, the output of IC501 (pin 7) will go
high and turn on Q504. Q504 will energize the coil of RL501. RL501 will latch "on" and remove
the voltage from terminal 3 and relay RLY101 (power supply board).
Thermal Overload
The transformer in this amplifier contains an internal temperature sensor. This sensor disables the
transmit function if the transformer's temperature ever happens to approach the limit of safe
operation. Thermal overload is indicated if the "OL" LED illuminates without the "XMT" LED
being illuminated.
The amplifier will not operate during a thermal overload indication. The thermal protection system
automatically resets after several minutes of a non-transmitting cool down period.
Cathode Warm-up Timer
Indirectly heated transmitting tubes normally require a few minutes of "warm-up" time before plate
current can be drawn. This protection is provided by IC501 (see Tube Life on page 10). Pin 2 of
IC501 is connected to a regulated reference voltage. C509 begins to charge when the main power
switch is placed in the ON position. The voltage at pin 3 of IC501 will exceed the voltage on pin 2
after approximately three minutes, causing the output of IC501 (pin 1) to go high.
Q503's collector pulls low whenever the output of IC501 (pin 1) is high. When the collector of
Q503 is low, Q502 and Q501 are forward-biased. This allows 12 volts to appear at terminal 5.
Terminal 5 supplies 12 Vdc to the keying circuits and the plate and grid current meter lamp.
Power Supply
Heater Supply
The heater circuit of this amplifier satisfies all requirements of the tube manufacturer related to tube
performance and life. The heater voltage and inrush current are controlled by the power
transformer's internal resistance and impedance, heater choke resistance, heater wiring resistance,
and the step-start circuit. For maximum tube life, NEVER replace any circuit components or wiring
with substitute parts. Always consult the factory before making modifications that may affect tube
life.
Plate (HV) Supply
The plate supply uses a full wave doubler circuit with 200 amp surge rated diodes and a heavy duty
32 pound grain oriented transformer with internal thermal protection. Filtering is accomplished by a
bank of high quality computer grade capacitors totaling 63 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).
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AL-800
Instruction Manual
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
two-ampere fast-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 Meters 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
0.05 ampere, a large picket every 0.25 ampere, and indicates 1.5 amperes at full deflection.
The left-hand meter scale indicates the grid current (Ig). The small pickets on this "Ig" scale appear
every 5 mA and the larger pickets appear every 25 mA. The full scale "Ig" reading is 125 mA.
The plate and grid meters in this amplifier will normally indicate maximum grid current and
maximum RF output near the same "PLATE" tuning setting during adjustments. Maximum grid
current and minimum plate current also generally occur at or near 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 overload circuit 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 highvoltage-to-chassis current fault. The grid and plate current meters will not read correctly if this
diode fails. The overload circuit may repeatedly trip before full power is reached if D117 is shorted.
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 serves multiple functions, including measurement of the high
voltage (HV), reflected power (REF), SWR, ALC voltage output (ALC), and relative ALC threshold
(ALC SET). These four metering functions are selected by the "MULTIMETER" switch. See
Multimeter Functions for more information.
Multimeter Functions
HV: The multimeter will indicate the dc plate voltage of the PA tube when in the HV position. The
correct scale to use is the ACL / HV scale, which has a picket every 100 volts. Two zeros must be
added behind the numbers indicated on the meter scale (i.e. multiply by 100), so that "25"=2500
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Instruction Manual
volts and "20"=2000 volts. Do not operate the amplifier if the high voltage is over 2700 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 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 can be measured when the "MULTIMETER" switch is in the REF
position by observing the different red SWR curves. The forward and reflected meter
pointers will cross each other on, or near, the correct SWR curve.
ALC: The multimeter measures the output voltage of the ALC detector when in the ALC position.
The full scale ALC reading is 35 volts and is read directly from the ACL / HV scale. The meter
should flick upwards occasionally during normal ALC action. See ALC Metering,
Controls, and Adjustments operation on page 19 for more information.
ALC SET: The multimeter measures the approximate grid current that will produce ALC activity
when the meter switch is in the "ALC SET" position. One zero must be added to the reading on
the ACL / HV scale and the result divided by 2 for this function. For example, ALC action will
begin at approximately 75 mA of grid current (typically between 60 mA and 90 mA) when the
"ALC SET" control is adjusted until the meter reads "15."
Wattmeter Circuit
The AL-800 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 can be obtained by subtracting the
reflected power from the forward power reading.
Peak Envelope Power vs. Average Power
Peak envelope power (PEP) is often misunderstood. PEP is not associated with the sine wave or
root-mean-square (RMS) power, and it has no fixed ratio to average power. There are no formulas
that allow accurate conversions between average and peak voice waveform power.
PEP is the power at the crest (highest point) of the RF waveform. On SSB, the average power can
vary from a few percent of the PEP to over fifty percent of the PEP. Generally, the PEP on SSB is
two to five times greater than the average power. On CW or other constant amplitude modes (such
as FM or RTTY), the PEP is always equal to the average power.
Tube Life
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The 3CX800A7 is a reasonably rugged tube. The anode can handle very large anode dissipation
overloads for short periods of time due to the thermal mass of the external anode. Care must be
taken to avoid exceeding the temperature ratings of the tube's ceramic-to-metal seals. The life of the
tube in this amplifier may be prolonged if adjustment periods are kept short and a brief "cool-down"
periods are provided between lengthy adjustment periods. Avoid shutting the main power off
immediately after lengthy full power CW or RTTY transmissions. After lengthy full power RTTY
or CW transmissions, allow a one or two minute "cool-down" period (without transmitting) before
shutting off the ac power switch.
The most sensitive element in any indirectly heated oxide cathode tube will always be the control
grid. A fraction of a second of incorrect tuning can cause control grid damage. This is especially
true in amplifiers that use fuses or resistors to protect the grids. Fuses and resistors are much too
slow and too unpredictable to adequately protect control grids. In this amplifier, the 3CX800A7 grid
is protected by a fast-acting electronic circuit. This circuit rapidly disables the amplifier when
excessive grid dissipation occurs. Never remove or defeat this circuit. Doing so will void the
manufacturer's warranty.
In the AL-800, a grid current of 75 mA (at 100 watts of drive) produces the maximum rated grid
dissipation of 4 watts. This amount of grid current will also safely disable the amplifier within a few
milliseconds.
WARNING:
NEVER drive this amplifier with more than 100 watts of short term average envelope power.
NEVER remove, defeat, or modify the internal electronic grid protection circuits.
Maximum power output normally occurs with a maximum of 15 to 20 mA of grid current on CW,
or 12 mA indicated (25 mA peak) during a SSB two-tone test. The grid dissipation is well under one
watt with 25 mA of grid current and 100 watts of drive.
The cathode of the 3CX800A7 must reach full operating temperature before the tube is operated.
The cathode becomes fully operational 180 seconds after the application of the full heater voltage.
The warm-up timer in this amplifier assures that the cathode reaches the proper operating
temperature before the amplifier can be operated. Never defeat the warm up timer or alter the heater
voltage.
The continuous commercial plate current rating of the 3CX800A7 is 600 mA. Brief periods of plate
current exceeding 1.2 amperes (during tuning) will not cause loss of emission or shorten the amateur
life of the tube in this amplifier. For maximum tube life, plate current should be maintained below
700 mA on normal amateur CW operation, 600 mA on FM, RTTY, and other "steady" carrier
modes. The life a metal oxide cathode is directly related to the accumulated heater operating
time, not the transmitting time.
The application of heater or filament voltage causes thermal stresses from rapid and uneven
temperature changes in the tube's heater. Avoid unnecessary main power switch cycling to prevent
needless heater life reduction.
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Instruction Manual
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, or during conditions of high anode voltage. 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, tube that have been stored for extended periods, or abused tube will increase the
likelihood of a "gas arc". Ameritron recommends using only current code date Eimac 3CX800A7
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.
Standard frequency ranges are indicated in the chart on page 32.
Technical Assistance
Technical assistance is available during normal central standard time business hours on weekdays.
Customer service is more effective when our engineers 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.
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CAUTION: Never ship this amplifier with the tube installed. Ameritron will not be
responsible for shipping damage caused by improper packing.
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Instruction Manual
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-800 ventilation system has been designed and tested to maintain tube seal temperatures
safely below the tube manufacturer's rating at 1200 watts of continuous two tone test SSB PEP
output, or 850 watts of continuous RTTY, FSK, FM or CW power output when the amplifier is
properly tuned. The blower in the AL-800 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-800 is supplied with a NEMA 5-15P plug for 120 Vac operation. The Transformer
Connections section on page 15 show the correct wiring for various supply voltages.
This amplifier has a current demand of approximately 16 amperes at 120 Vac with 1200 watts of
carrier output and an absolute maximum draw of 20 amperes under severe operating conditions.
The average power line current during voice peaks on SSB will be approximately 6 amperes at 1200
watts PEP output. Most normal residential power lines and house-wiring should meet this demand
for current.
If the power mains have excessive resistance, the high voltage may sag to less than 2200 volts under
load. Voltage sag will not hurt the life of the amplifier components if the fully loaded high voltage
remains above 2000 volts. 240 volt operation will help improve performance if the power wiring is
marginal.
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AL-800
Instruction Manual
CAUTION: Never allow the high voltage to exceed 2700 volts under any condition.
For 120 volt operation, the wiring between the fuse box and the amplifier ac outlet must be number
12 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 properly for the gauge of house-wiring used, but
never exceed 25 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 flexible. Braided or woven conductors
offer a high impedance to both lightning and RF.
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 to the water supply line. 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 to both RF and
lightning currents. 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 wide, smooth
conductors.
2.) Avoid routing a single small gauge grounding 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 grounds 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 outside ground on the antenna side of the choke.
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AL-800
Instruction Manual
Transformer Connections
The power transformer of the AL-800 has fourteen different voltages available on the primary and is
rated at full power with supply frequencies of 50 to 60 Hz and voltages above 100 volts. The
Jumper Connections chart below indicates the proper placement of jumpers for various
power line voltages.
Jumper Connections
CONNECT A JUMPER FROM THE BOLD COLUMN HEADING LETTER ("A" - "F") TO
THE LETTER OR NUMBER IN THE ROW NEXT TO THE DESIRED "HIGHEST LINE
VOLTAGE". DANGER: Never change jumpers with the power cord connected to an outlet.
Line
Highest
"A"
"B"
"C"
"D"
"E"
"F"
Fuse
Line-V
205
C
(B)
3
1
12
215
C
(B)
3
2
12
220
C
(B)
2
1
12
230
C
(B)
F
(E)
10
240
C
(B)
1
2
10
245
C
(B)
2
3
10
250
C
(B)
1
3
10
90
(B)
100
(B)
110
(B)
115
(B)
125*
(B)
130
(B)
140
(B)
* Factory wired
A
A
A
A
A
A
A
(D)
(D)
(D)
(D)
(D)
(D)
(D)
C
C
C
C
C
C
C
3
3
2
F
1
2
1
1
2
1
(E)
2
3
3
25
25
25
20
20
20
20
WARNING:
The AL-800 requires different back panel fuses for various line voltages. Use the fuse listed
in the JUMPER CONNECTIONS chart for maximum protection.
Interconnections
1.
Connect the exciter's RF output to the "RF IN" connector on the rear of the AL-800 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.
16
AL-800
2.
3.
Instruction Manual
Connect the existing station antenna system to the "RF OUT" connector on the rear of the AL800 with RG-8 type coax. This amplifier connection uses a SO-239 female that mates with a
PL-259 connector on the cable.
Shielded audio type cable with a standard male phono plug should be used to connect to the
"RLY" jack on the AL-800. 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-800 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. The ALC section describes adjustment of this circuit in detail.
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 0-175 mA. See the Meters 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
blower should start, the right-hand meter should be illuminated, and high voltage should appear.
The left-hand meter should illuminate and the amplifier should operate after three minutes.
"STBY-OPR" Switch
This switch disables the amplifier's internal antenna relay and resets the grid protection circuit. In
the "STBY" position the amplifier is bypassed without turning the tube's heater or the power supply
off.
This switch will also reset the grid protection circuit if the "OL" LED is illuminated. The overload
circuit is automatically reset whenever this switch is placed in the "STBY" position and returned to
the operate position.
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AL-800
Instruction Manual
"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. This adjustment is necessary to
insure optimum coupling to 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 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 drivepower applied. Never use this control to adjust the output power.
CAUTION:
Failure to adjust the loading control properly can result in excessive tank
circuit voltages and damage to components.
The "PLATE" control should always be checked after the "LOAD" control is adjusted by more
than one number. For example, if the "LOAD" is advanced from 1-1/2 to 2-3/4, the "PLATE"
should be re-tuned. If the "LOAD" is touched up a small amount, the "PLATE" setting will not
usually require re-adjustment.
Driving Power
This amplifier is designed to operate at full ratings when it is driven by an exciter that has
approximately 85 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 85 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-800's internal meter. Determine the maximum obtainable RF output power and reduce
the exciters 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.
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AL-800
Instruction Manual
The amplifier 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 tube and other components than operating a
properly loaded amplifier into a high SWR or with excessive drive power.
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 25 mA of grid current on CW carrier. The proper grid current during voice
modulated SSB will range from 0 to 12 mA, and will typically be at 5 mA or less. The SSB
grid current will vary with the operators voice, the amount of signal compression or processing,
and the tube characteristics.
Additional SSB Notes
The peak power output developed on SSB is limited by the amplifier loading, RF drive, and peakto-average power of the RF wave form. The "LOAD" setting is the single most critical adjustment
for proper operation. Properly loaded, this amplifier will produce excellent linearity with output
powers of well over one kilowatt. Improperly adjusting the "LOAD" control can produce flattopping and splatter with only a few hundred watts of RF output.
Note:
Always remember that the "LOAD" control setting is much more important than any other
parameter for good linearity!
To maintain linearity, always be sure that the "LOAD" control is adjusted far enough clockwise for
the peak drive that will be applied.
Be considerate of others. NEVER "push" this amplifier into envelope clipping or to the point where
the grid current approaches 12 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
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AL-800
Instruction Manual
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 on voice
peaks.
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 65%, the carrier efficiency must be kept below 30% to maintain
linearity. The power dissipated in the tube anode will be more than twice the carrier output power.
The carrier power must be kept below 150 watts for clean and safe AM operation. With 150 watts
of carrier, the peak envelope power will reach 600 watts with 100% symmetrical modulation. The
modulated AM power output should be limited to 1200 watts peak with non-symmetrical
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.
FM (Frequency Modulation), RTTY, and DIGITAL OPERATION
The efficiency of this amplifier will approach 65% 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.
ALC Metering, Controls, and Adjustments
ALC Metering Functions
The "MULTIMETER" switch in the AL-800 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 "ACL / 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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AL-800
Instruction Manual
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 "ACL / HV" scale and the result
divided by 2 for this function.
For example: If the meter reads 15, add one zero (150) and divide by 2 (75). In this example ALC
action will begin at approximately 75 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 3 to 6 volts with the
"MULTIMETER" switch in the "ALC SET" position. This will allow a maximum grid current
of approximately 15 to 30 mA.
ALC Adjustments
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 20 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 20 mA of grid current with any tuning or drive adjustment.
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 25 mA under any tuning or drive
adjustment condition. During proper CW ALC operation, the exciter drive level control should be
21
AL-800
Instruction Manual
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 adjust to the limit required by the exciter.
If the ALC voltage requirements are low and 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.
An external 1,000 to 5,000 ohm potentiometer can be added from the ALC output line to ground if
the particular amplifier you are using does not have a rear panel "ALC Limit" control. The chassis
(shield) of the amplifier's ALC output jack must connect to the clockwise (shaft end view) terminal
of the ALC exciter voltage control. The ALC jack center pin on the amplifier must connect to the
counter-clockwise terminal (shaft end view) of the external control. The center of the control
connects to the ALC input of the exciter.
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).
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AL-800
Instruction 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.
"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 .8 A of short duty cycle (or .6 A of long duty cycle) plate
current. Never exceed 25 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 section on page 6, and the Multimeter section on page 9.
Tuning
Follow the instructions below in numerical order. 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.
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.
Tuning Procedure
Important Note: This amplifier contains an electronic grid protection circuit to prevent control-grid
damage. This amplifier will quit operating and the "OL" LED will illuminate if the grid dissipation
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
23
AL-800
Instruction Manual
increase on the grid current meter. The grid overload circuit can be reset by momentarily placing
the "STBY-OPR" switch in the "STBY" position.
Some exciters generate high-level RF pulses when first keyed. These short duration pulses may
greatly exceed the exciter's steady-state operating output power. Unexplained activation of the grid
overload circuit may indicate the existence of this 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 probably indicates the
"LOAD" control is set too low.
1.
Set the AL-800 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 2500 volts
nominal and no more than 2700 volts.
4.
With the amplifier still on "STBY", tune the exciter into a normal 50 ohm load according to
the manufacturer's instructions. 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:
Frequency
1.810
3.600
7.050
10.125
14.050
18.125
21.050
24.900
28.050
CW
Plate
3-1/2
1-3/4
5
5-1/2
8
8
9
8-1/2
9
Load
6-1/4
0-1/2
1-3/4
2-1/2
6
5-1/2
6-1/2
6-1/2
7-1/2
24
AL-800
Frequency
1.850
3.900
7.200
14.250
21.350
28.500
Instruction Manual
PHONE (SSB)
Plate
3-1/2
3
5-1/4
8-1/4
9-1/4
9
Load
7
3-1/2
4-3/4
6
6-1/2
7-1/2
6.
With the exciter's drive level still on zero, observe the 1.5 ampere 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 the 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 (Ip) should suddenly jump from zero to nearly 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 5 volts. This adjustment will limit the
amplifier's grid current to approximately 25 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 number 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 30 mA OR THE PLATE CURRENT
(Ip) TO EXCEED .6 AMPERES AT THIS STAGE OF TUNING. If either current exceeds these
limits, reduce the exciter's power. Adjust the "PLATE" control for maximum output power.
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AL-800
Instruction Manual
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 15 mA or a plate current of 0.3 ampere (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 now dip slightly. The drive power
should be removed.
11a. Increase the "ALC SET" voltage (if the ALC is connected) until 35 mA (7 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 40 mA at this
stage. The plate current should not be allowed to exceed 1 ampere during brief periods of
tuning (30 seconds).
11b. Increase the exciter drive power (if the ALC is not connected) until 35 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 40 mA at this stage. The plate current should
not be allowed to exceed 1 ampere during brief periods of tuning (30 seconds).
12. For CW operation, the output power should be reduced with the "ALC SET" control until the
rated power of 850 watts CW is obtained. The "LOAD" control should be adjusted until
minimum plate current is obtained without dropping below 850 watts. 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.
13. For SSB operation, a two-tone generator or sustained "HEL-L-L-L-L-O" can be used. The
exciter should be set to produce the maximum output power (not to exceed 100 watts of peak
power). The amplifier's "LOAD" control is adjusted for maximum power on the internal peak
reading RF wattmeter. The "ALC SET" control is adjusted until a peak power output of 1200
watts (or less) is obtained. Finally the exciter's audio gain or output power is adjusted until the
multimeter "ALC" position indicates the desired ALC level.
Note:
If the ALC is not connected, the amplifier should be fully loaded with maximum drive (not
to exceed 100 watts). The exciter's output should then be reduced until 1200 watts is
obtained.
QSK Operation
The antenna transfer relay in the AL-800 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 high-speed
26
AL-800
Instruction Manual
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-800. 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.
WARNING:
High voltages 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 anodes (outer metal surface) to the chassis before touching anything
inside the amplifier.
6.) ALWAYS be cautious of heat.
temperatures.
27
Many components inside the amplifier operate at high
AL-800
Instruction Manual
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.
Parts List
Timer / Overload Board (50-0117-2)
Designator
C501-506
C507,508
C509
D501, 502
D503
IC501
Q501
Q502, 504
Q503, 505
R501-503
R504, 505
R506, 508
R507
R509
R510
R511
R512, 513
R514, 515
RLY501
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
4.7k 1/4 W
470 ohm 1/4 W
DPDT 12 V dip relay
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
100-3470
100-2470
408-2135
28
AL-800
FB
29
Instruction Manual
FB 73-801 Ferrite Bead
10-15168
AL-800
Instruction Manual
Power Supply / SWR Board (50-0800-1)
Designator
D101, 102, 114, 115
D103
D116 - 120
D104 - 113
C101
C102
C103
C104
C105,125,126,129,135 - 137
C139
C107 - 116
C118 - 123
C127
C106, 128, 138, 140
C130, 131
C133
C134
R101
R102
R103,104,122
R105
R106
R107,131
R108,109
R110,111
R113-118
R120
R121
R123
R124,125
R126, 128, 129
R127
R130
RLY101
RLY102
RFC101
T101
Q101
Q102
Q3 (see main chassis)
F101
Description
1N34A
1N752, 5.6V
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
380 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
3 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%
51 ohm 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 W
3PDT 12 Vdc
SPST 12 Vdc
Choke 3 turns FB-73
Toroid
2N3904
2N3906
2 A slow blow
Ameritron P/N
300-0346
305-0710
300-0266
300-0145
208-5404
200-2120
200-3531
204-0150
200-0416
203-0530
200-2121
203-0682
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
101-4470
408-6140
408-6148
10-15168
10-14134
305-0645
305-0722
755-1102
30
AL-800
Instruction Manual
Meter Board (50-0800-3)
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
R316
IC301
Q301, 302
Q303
S301
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
47k 1/4 W
LM324
2N3904
2N3906
Rotary 2P6T
Ameritron P/N
300-0346
203-0530
200-0754
200-2120
100-6220
100-0390
100-1200
100-0188
100-4100
100-2100
100-3330
100-1470
100-0330
100-0600
100-4470
311-0324
305-0645
305-0722
500-0563
Tuned Input Board (50-0800-2)
Designator
C202 (tube side)
C201 (transmitter side)
L201
S201
Description
See input chart
See input chart
See input chart
Input switch
Ameritron P/N
AL-800 Tuned Input Chart
S201
1
2
3
4
5
6
*
31
BAND
160
80
40
20/30
15/17*
10/12
Capacitor (pF) Input
1600, (208-5455), C201
1300, (208-5177), C203
470, (208-5440), C205
220, (208-5175), C215
330, (208-5331), C207
150, (208-5151), C209
100, (208-5174), C211
150pF, (208-5151), C214
220pF, (208-5175)
4T Air Coil, L207
Inductor
21.75, (405-1217), L201
18.75, (405-1187), L202
10.75, (405-1107), L203
Capacitor (pF) Output
1300, (208-5177), C202
1000, (208-5176), C204
500, (208-5691), C206
5.75, (405-1057), L204
3.75, (405-1037), L205
4.75, (405-1047), L206
330, (208-5331), C208
220, (208-5175), C210
68, (208-5395), C212
AL-800
Instruction Manual
AL-800 Main Chassis Parts List
Designator
B1
C1, 6
C2, 3, 9
C4, 5, 17
C7
C8
C16, 21
C11-13, 18-19
C 14, 15
F1,2
50-0080-1
50-0080-2
50-0080-3
50-0080-4
50-0117-2
L1
L2
L3
M1
M2
R1
R2
R3
R4, 5
R6
PC1
RFC2
RFC3
RFC4
RFC5
S1
S2
S3
S4
Q3
T1
V1
Description
Blower
170 pF Doorknob 7.5 kV
.001 uF 7.5 kV
470 pF 3 kV chip capacitor
Air Variable Load
Air Variable Plate
.01 uF 1 kV disc
.1 uF 50 V disc
.01 uF 250 Vac disc
See Line Voltage Chart, page 6
Power Supply / SWR Board Assembly
Input Circuit Assembly
Metering Board Assembly
RF Tank Board Assembly
Timer / Overload Board Assembly
"L " Coil
LF Coil
HF Coil
Meter (current, grid and plate)
Meter (multimeter and power output)
100 k pot (ALC limit)
1 k pot (ALC SET)
33 ohm 1/2 W
.6 ohm 3W
100 ohm 50 W
Parasitic Choke
Plate Choke
2.5 mH Choke
Cathode Choke
Filament Choke
Band Switch
Lighted switch
Rocker Switch
Interlock Switch
Transistor MJF3055
Transformer
3CX800A7 Tube
Ameritron P/N
410-3590
209-0559
200-7224
210-0470
204-2573-1
204-2112
200-2121
200-0754
200-2122
-------------50-0800-1
50-0800-2
50-0800-3
50-0800-4
50-0117-2
10-13800-LC
10-13800-LF
10-13108
400-3580
400-3581
105-1341
105-7301
100-403
103-3399
103-9588
10-15106
10-15139
402-1162
10-15120
10-15120-1
504-2135
507-1157
507-1147
504-3247
305-3055
406-1248
350-0800
32
AL-800
Instruction Manual
Frequency Coverage
AL-800
160 meters
80 meters
40 meters
20 meters
15 meters
AL-800X
1.8-2.0 MHz
3.3-4.4 MHz
6.3-8.3 MHz
10.1-15.5 MHz
16.5-21.5 MHz*
160 meters
1.8-2.0 MHz
80 meters
3.3-4.4 MHz
40 meters
6.3-8.3 MHz
20 meters
10.1-15.5 MHz
15 meters
16.5-21.5 MHz*
10 meters
24-29 MHz*
* Operation on 11-13 MHz, 15.5-16.5 MHz, and 25-27.9 MHz will damage components.
Amplifier Tuning Log
Band
160 CW
160 SSB
80 CW
75 SSB
40 CW
40 SSB
30 CW
20 CW
20 SSB
17 CW
17 SSB
15 CW
15 SSB
"LOAD"
"PLATE"
Fill in this log with the amplifier settings to quickly change bands. Use a pencil as settings may
change with different antennas.
Notes:
33
AL-800
Instruction Manual
Schematics
Power Supply / SWR Board
34
AL-800
Tuned Input Board
35
Instruction Manual
AL-800
Instruction Manual
Meter Board
36
AL-800
Timer / Overload Board
37
Instruction Manual
AL-800
Instruction Manual
Main Chassis
38
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