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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AL-800 |
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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Instruction Manual |
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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Instruction Manual |
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:
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:
Efficiency:
CW:
SSB:
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:
Tube:
Type:
Continuous dissipation:
Warm-up time:
Estimated life:
Pi-network, slug tuned coils 1.3:1 or less
20% of center frequency
100 watts PEP
85 watts
Pi-L, Pi-network 1200 + watts
850 watts
1200 watts
700watts
1.8to 21 MHz amateur Bands. (Export models include 24.5 and 28 MHz)
-35 dB or better (at rated output)
approximately 65%
approximately 65% (envelope crest)
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
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: |
SO-239 |
Line: |
NEMA 5-15P, standard 120 V three wire |
Others: |
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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Instruction Manual |
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: 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.
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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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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
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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AL-800 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
10
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