Ameritron AL-800H Service manual
AL-800H Instruction Manual
NEVER APPLY POWER TO THIS AMPLIFIER WITH THE COVER REMOVED!
WARNING!!
CONTACT WITH THE VOLTAGES INSIDE THIS AMPLIFIER CAN BE FATAL!
PLEASE READ THIS MANUAL BEFORE ATTEMPING TO OPERATE
EQUIPMENT! Improper or abusive operation of this amplifier can damage the tubes
or other components in this amplifier. Damage caused by improper or abusive
operation is not covered under the warranty policy.
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AL-800H Instruction Manual
Unpacking Instructions
Remove the 3CX800A7 tubes from their shipping cartons. Carefully unwrap the tubes and inspect them for
visible damage. look for dented anode coolers and broken or bent pins. Roll the tubes 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 Philips screwdriver. Save the screws to resecure the
cover. carefully lift the rear of the cover while sliding the cover back. TheAL-800H is shipped with the
rubber chimneys, fusses, 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 tubes must be installed in their sockets prior to operation. Observe the pin configuration on the tubes
and the sockets. Two of the pins are separated by a large space. Carefully observe the pin alignment to be
sure the tube pins are centered on the socket's metal contacts. Firmly press each tube into a socket. Do
NOT twist or force the tubes into the sockets.
Install the rubber chimneys over the tubes. The seam of the chimneys 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.
Remove the tape holding the anode connectors to the center panel. Install the anode spring clip connectors
on the tube's anode caps by pushing straight down on the clips.
The top cover should now be installed with the side ventilation holes positioned on the lift (front view).
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 screw's 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 15A fuses for standard
240 Vac operation. If you wish to operate the amplifier on a line voltage other than 240 Vac, 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 13 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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AL-800H Instruction Manual
Table of Contents
Unpacking Instructions....................................................................................................iv
Features ........................................................................................................................... 1
AL-800H Technical Specifications.................................................................................2
General Information ........................................................................................................3
Safety Interlock....................................................................................................3
ALC.....................................................................................................................4
Dynamic Bias ......................................................................................................4
Timer - Overload Circuits ...............................................................................................5
Grid Overload Protection ....................................................................................5
Thermal Overload................................................................................................5
Cathode Warm-up Timer.....................................................................................5
Power Supply ..................................................................................................................6
Heater Supply......................................................................................................6
Plate (HV) Supply ...............................................................................................6
Meters..............................................................................................................................6
Current Meter (plate and grid):............................................................................6
Multimeter...........................................................................................................7
Multimeter Functions.......................................................................................... 7
Wattmeter Circuit................................................................................................7
Peak Envelope Power vs. Average Power........................................................... 8
Tube Life......................................................................................................................... 8
Export Modifications.......................................................................................................9
Technical Assistance.......................................................................................................10
Installation Guidelines and Suggestions..........................................................................11
Location Of The Amplifier.................................................................................11
Ventilation...........................................................................................................11
Power Connections.............................................................................................. 11
Grounding............................................................................................................12
Transformer Connections................................................................................................13
Interconnections .............................................................................................................. 13
Operating Instructions And Guidelines...........................................................................14
Front Panel Controls............................................................................................14
"MULTIMETER" Switch........................................................................14
"OFF-ON" Switch...................................................................................14
"STBY-OPR" Switch ..............................................................................14
"PLATE" Control....................................................................................15
"LOAD" Control .....................................................................................15
ALC Metering, Controls, and Adjustments.....................................................................15
ALC Metering Functions.....................................................................................15
ALC Controls...................................................................................................... 16
ALC Adjustments................................................................................................16
Rear-panel "ALC LIMIT" control....................................................................... 17
ALC Limit Adjustment (rear panel)....................................................................17
Driving Power .................................................................................................................18
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AL-800H Instruction Manual
Tube and Component Life............................................................................................... 18
Tuning ............................................................................................................................. 19
Tuning Procedure................................................................................................19
"ALC SET" Control ............................................................................................ 22
Additional SSB Notes .....................................................................................................22
AM (Amplitude Modulation) Operation.........................................................................22
FM (Frequency Modulation), RTTY, and DIGITAL OPERATION ..............................23
Audio Distortion.............................................................................................................. 23
QSK Operation................................................................................................................ 23
Periodic Maintenance......................................................................................................24
Parts List..........................................................................................................................25
Power Supply / SWR Board (50-0800H-1).........................................................25
Tuned Input Board (50-0800H-2) .......................................................................26
AL-800H Tuned Input Chart...............................................................................26
Meter Board (50-0800H-3)..................................................................................26
Timer / Overload Board (50-01172)....................................................................27
AL-800H Main Chassis Parts List.......................................................................28
Frequency Coverage........................................................................................................29
Amplifier Tuning Log .....................................................................................................29
Notes: ..................................................................................................................30
Schematics....................................................................................................................... 31
Wiring Diagram................................................................................................... 31
PWR Supply / SWR Board ................................................................................. 32
Input Board..........................................................................................................33
Meter Board......................................................................................................... 34
Timer / Overload Board ......................................................................................35
Notes: ..................................................................................................................36
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AL-800H Instruction Manual
Features
• The AL-800H uses two reliable high gain 3CX800A7 tubes.
• A time-delay circuit provides a 180 second warm-up to eliminate potential damage to the tube
cathodes.
• 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 tubes or other
components.
• A thermal overload automatically disables the amplifier if excessive heating of the power transformer
occurs.
• A multi-voltage heavy-duty transformer with a unique "buck-boost" winding allows adjustment of
the primary voltage to 14 different voltages centered on 115 and 230 volts. This versatile Ameritron
feature allows the user to select the optimum primary voltage for maximum performance and life.
• The tuning and loading controls have vernier 6:1 reduction drives for smooth tuning. Logging scales
allow quick and repeatable control adjustment for rapid band changes.
• The AL-800H 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 scales.
• Heater and plat voltages are maintained using the "STBY/OPR" switch. This allows the amplifier to
be conveniently bypassed for "barefoot" operation.
• A front panel "ALC SET" control allows convenient adjustment of the ALC threshold. The unique
ALC circuit samples the grid current and power supply voltage.
• "XMT" and "OL" LED's on the front panel indicate proper operation of the amplifier.
• A rear panel 12 volt auxiliary output jack provides up to 200 mA at 12 Vdc for accessories such as the
ART-15 Antenna Tuner.
• 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-800H Instruction Manual
AL-800H Technical Specifications
Input:
Circuit type: Pi-network, slug tuned coils
Maximum VSWR at resonance: 1.3:1 or less
Minimum 2:1 VSWR bandwidth: 20% of center frequency
Maximum drive power permissible: 100 watts PEP
Typical drive for full power output: 55 watts
Output:
Circuit type: Pi-L, Pi-network
Typical SSB PEP voice operation: 1500 watts
CW continuous operation: 1500 watts
1/2 hour PEP two-tone test: 1500 watts
1/2 hour continuous carrier (RTTY): 1000 watts
Frequency Coverage: 1.8 to 21 MHz amateur Bands. (Export models include 24.5 and 28 MHz)
Third Order IMD: -35 dB or better (at rated output)
Efficiency:
CW: approximately 65%
SSB: approximately 65% (envelope crest)
Power Supply:
Circuit type: Full wave voltage doubler
No load voltage: 2600 V
Full load voltage: 2250 V
Full load current: 1.2 A
Regulation: 15%
Transformer: 32 lb. E-I lamination grain oriented
Capacitors: 63 mFd total, computer grade
Normal line current at rated CW output: 14A at 240 Vac
Normal line current at 1500 watt PEP output: 9 A at 240 Vac
Power line current in standby: 0.5 A at 240 Vac
*
Tube:
Type: (2) 3CX800A7
Continuous dissipation: 800 watts total per tube, 1600 watts total
Warm-up time: 180 seconds
Estimated life: 8,000 hours ICAS
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 6-15P, standard 240 V three wire
Others: RCA Phono
Physical:
Dimensions: 17-1/4"D x 14-1/2"W x 8-1/2"H
Weight: 60 lbs. shipping (52 lbs. operating)
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AL-800H Instruction Manual
Ameritron Al-800H 1500 Watt Linear Amplifier Instruction Manual
The Ameritron AL-800H is a 1500 watt output linear amplifier that operates from 160 through 15 meters.
The AL-800HX is the export model that operate from 160 through 10 meters. Export modification
instructions are only available with proof of a valid amateur radio license.
The AL-800H uses a pair 3CX800A7 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, electronic grid current and thermal overload protection, and automatic bias
switching to make this the best featured and most reliable 3CX800A7 amplifier available. The AL-800H
and AL-800HX are 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.
General Information
Safety Interlock
The top cover of the AL-800H operates an interlock switch which completes the primary circuit of the
power transformer. The interlock will open and de-energize 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.
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AL-800H Instruction Manual
ALC
The AL-800H 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).
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-800H 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-800H 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.
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AL-800H Instruction Manual
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: 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.
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 8). 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
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AL-800H Instruction Manual
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 modifying any section of this amplifier
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 13 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 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 high-voltage-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
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AL-800H Instruction Manual
The multimeter is the meter on the right. It continuously reads the forward peak envelope power on its lefthand 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 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 13 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 15 for more information.
ALC SET: The multimeter measures the approximate grid current that will produce ALC activity when
the meter switch is in the "ALC SET" position. One zero must be added to the reading on the 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-800H 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
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AL-800H Instruction Manual
Peak envelope power (PEP) is often misunderstood. PEP is not associated with the sine wave or root-meansquare (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
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. The 3CX800A7 grids in this amplifier are protected by a fast-acting
electronic circuit. This circuit rapidly disables the amplifier when excessive grid dissipation occurs.
In the AL-800H a grid current of 150 mA (at 100 watts of drive) produces the maximum rated grid
dissipation of 4 watts per tube. This amount of grid current will also safely disable the amplifier within a
few milliseconds. Never remove or defeat the grid protection circuit. Doing so will void all
manufacture's warranties.
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 40 to 60 mA of grid current on CW, or 25
mA indicated (50 mA peak) during a SSB two-tone test. During typical SSB voice operation, the grid
current usually moves slightly above zero. The grid dissipation is well under one watt with 50 mA of grid
current and 100 watts of drive is around on watt per tube.
The cathodes of the 3CX800A7's must reach full operating temperature before the tube is operated. The
cathodes become fully operational 180 seconds after the application of the full heater voltage. The warmup 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.
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