Ameritron AL-80B Service manual

AL-80B Instruction Manual

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 tubes or other components in

this amplifier. Damage caused by improper or abusive operation is not covered under the

warranty policy.

AL-80B Instruction Manual

Unpacking Instructions

Remove the 3-500Z tube from its shipping carton. Carefully inspect the tube for visible damage. Look for bent or broken pins. Roll the tube over slowly while listening and watching for loose internal materials. Be sure the anode is not off center at the end away from the anode connector. 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-80B is shipped with the fuses and fuse caps packed inside the amplifier. Additional screws will be included in the fuse pack if they are required.

WARNING:

The tube must be installed in its socket prior to operation. Observe the pin configuration on the tube and the socket. One of the pins is separated by a large space from the other four pins. Carefully observe the pin alignment to be sure the tube pins are centered on the socket's holes. Firmly press the tube into the socket. Do NOT twist or force the tube into the socket.

Install the anode connector on the tube's anode terminal and secure it with the screw provided. Snug the screw enough to secure the anode connector. Do not over-tighten the screw.

Install the fuses and fuse caps on the back of the amplifier. This amplifier uses two 20A fuses for standard 120 Vac operation (models B and BY) or two 10A fuses for 240 Vac operation (model BX only). If you wish to operate the amplifier on a line voltage other than 120 Vac, the jumpers on the power transformer primary windings must be changed. If the primary wiring is changed, the correct fuses must be installed. See the "Transformer Connections" section on page 12 for more information.

CAUTION :

Never remove the cover while this amplifier is connected to the power mains! Contact with the voltages in this amplifier can be fatal.

Always use fast-blow fuses rated at 250 Vac or higher. NEVER use standard automotive glass fuses or slow-blow fuses.

The top cover should now be installed with the side ventilation holes positioned on the left (front view). The ventilation holes on the top of the cover should be on the right side of the amplifier (front view). Secure the cover by installing the corner screws first. Install all the screws loosely until every screw is in place. Tighten the screws after they have all been installed.

Note: Save all packing materials for future shipping. The packing materials used to ship this

amplifier are specially designed to prevent damage. Replacement packing materials may be purchased from Ameritron if original packing materials are unavailable. Ameritron will NOT be responsible for re-shipping damage due to improper packing.

AL-80B Instruction Manual

Ameritron AL-80B

1000 watt PEP Linear Amplifier Instruction Manual

Features........................................................................................................................................1

AL-80B Technical Specifications................................................................................................2

Introduction..................................................................................................................................3

Safety Interlock................................................................................................................3

Circuit Descriptions.....................................................................................................................4

ALC..................................................................................................................................4

Dynamic Bias...................................................................................................................4

Power Supply...............................................................................................................................5

Filament Supply...............................................................................................................5

Plate (HV) Supply............................................................................................................5

Meters ..........................................................................................................................................5

Current Meter (plate and grid):........................................................................................5

Multimeter........................................................................................................................6

Multimeter Functions.......................................................................................................6

Wattmeter Circuit.............................................................................................................7

Peak Envelope Power vs. Average Power .......................................................................7

Tube Life......................................................................................................................................8

Export Modifications...................................................................................................................9

Technical Assistance....................................................................................................................9

Installation Guidelines And Suggestions.....................................................................................10

Location Of The Amplifier..............................................................................................10

Ventilation........................................................................................................................10

Power Connections ..........................................................................................................10

Grounding........................................................................................................................11

Transformer Connections.............................................................................................................12

Interconnections...........................................................................................................................13

Operating Instructions And Guidelines........................................................................................13

Front Panel Controls........................................................................................................13

"MULTIMETER" Switch....................................................................................13

"OFF-ON" Switch................................................................................................13

"STBY-OPR" Switch...........................................................................................14

"PLATE" Control.................................................................................................14

"LOAD" Control..................................................................................................14

ALC Metering, Controls, and Adjustments.....................................................................14

ALC Metering Functions.....................................................................................14

ALC Controls.......................................................................................................15

ALC Adjustments ................................................................................................15

Rear-panel "ALC LIMIT" control....................................................................................16

ALC Limit Adjustment (rear panel).................................................................................17

Driving Power..............................................................................................................................17

Tuning..........................................................................................................................................18

Tuning Procedure.............................................................................................................18

iii

AL-80B Instruction Manual

Additional SSB Notes..................................................................................................................22

AM (Amplitude Modulation) Operation......................................................................................22

FM (Frequency Modulation), RTTY, and Digital Operation.......................................................22

Audio Distortion ..........................................................................................................................22

QSK Operation.............................................................................................................................23

Periodic Maintenance...................................................................................................................23

Parts List ......................................................................................................................................25

Power Supply / SWR Board (50-0080-1).......................................................................25

Tuned Input Board (50-0080-2).......................................................................................26

AL-80B Tuned Input Chart..............................................................................................26

Meter Board (50-0080-3).................................................................................................26

Timer / Overload Board (50-0080-5)...............................................................................27

Al-80B Main Chassis Parts List.......................................................................................28

Frequency Coverage.....................................................................................................................29

Amplifier Tuning Log..................................................................................................................29

Notes................................................................................................................................30

AL-80B Instruction Manual

Features

• The AL-80B uses a rugged, inexpensive 3-500Z tube.

• The 3-500Z requires only a few seconds of warm-up time.

• A dynamic bias circuit eliminates hundreds of watts of unnecessary heat generation in the

power amplifier tube. The result is cooler operation and longer component life.

• A multi-voltage heavy-duty transformer with a unique "buck-boost" winding allows

adjustment of the primary voltage to 14 different voltages centered on 115 and 230 Vac. This versatile Ameritron feature allows the user to select the optimum primary voltage for maximum performance and life.

• The tuning and loading controls have vernier 6:1 reduction drives for smooth tuning.

Logging scales allow quick and repeatable control adjustments for rapid band changes.

• The AL-80B has two illuminated cross-needle panel meters. The left meter provides a

continuous reading of grid and plate currents. The right meter indicates 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.

• Filament and plate voltages are maintained using the "STBY/OPR" switch. This allows the

amplifier to be conveniently bypassed for "barefoot" operation.

• A front panel "ALC SET" control allows convenient adjustment of the ALC threshold. The

unique ALC circuit samples the grid current and power supply voltage.

• An "XMT" LED on the front panel indicates proper keying of the amplifier by the exciter.

• A rear panel "12 V" auxiliary output jack provides up to 200 mA at 12 Vdc for accessories

such as the ATR-15 Antenna Tuner.

• A step-start circuit limits the inrush current to the power supply and tube filament. This circuit

extends the life of the amplifier components.

AL-80B Instruction Manual

AL-80B 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: 85 watts

Output:

Circuit type: Pi-L, Pi-network Typical SSB PEP voice operation: 1000+ watts CW continuous operation: 800 watts 1/2 hour PEP two-tone test: 850 watts 1/2 hour continuous carrier (RTTY): 500 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: 3100 V Full load voltage: 2700 V Full load current: .6 A Regulation: >13% Transformer: 26 lb. E-I lamination grain oriented Capacitors: 26 mFd total, computer grade Normal line current at rated CW output: 12 A at 120 Vac Normal line current at 1000 watt PEP output: 8 A at 120 Vac Power line current in standby: 1 A at 120 Vac

Tube:

Type: 3-500Z Continuous dissipation: 500 watts Warm-up time: 10 seconds Estimated life: 12,000 hours ICAS

Metering:

Multimeter: Peak forward power (continuous). The second scale switches between peak reflected

power (and SWR), ALC threshold, ALC output voltage, and high voltage.

Current meter: Plate and grid current (simultaneously) on separate scales.

ALC:

Negative going, 0 to 10 volts, adjustable.

Relay:

Requires contact closure or sink of +12 Vdc at 100 mA. Back pulse protected.

Connectors:

RF: SO-239 Line: NEMA 5-15P, standard 120 V three wire Others: RCA Phono

Physical:

Dimensions: 15-1/2" D x 14-1/2" W x 8-1/2" H Weight: 48 lbs.

AL-80B Instruction Manual

Introduction

The Ameritron AL-80B is an 800 watt CW, 1000 watt PEP output linear amplifier that operates on all Amateur bands from 160 through 15 meters. The AL-80BX and AL-80BY are export models that operate from 160 through 10 meters. Export modification instructions are available with proof of a valid amateur radio license.

The AL-80B uses a single 3-500Z 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, and automatic bias switching to make this the best featured and most reliable single 3-500Z amplifier available. The AL-80B and AL-80BY are factory-wired for 120 Vac, 50/60 Hz line voltage. The AL-80BX is factory wired for 240 Vac. All models are easily converted to other supply voltages between 90 and 250 Vac.

Safety Interlock

The top cover of the AL-80B 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 :

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 several minutes for the capacitors to discharge after unplugging the

amplifier and before removing the cover.

4. ALWAYS select the high-voltage (HV) function of the Multimeter to check the high voltage potential. Do not remove the cover if voltage is indicated.

5. ALWAYS ground the tube anode (top metal conductor) to the chassis before touching anything inside the amplifier.

6. ALWAYS be cautious of heat. Many components inside the amplifier operate at high temperatures.

High voltage can kill!! Accidental contact with the voltages in this amplifier can be lethal!!!

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.

AL-80B Instruction Manual

Circuit Descriptions

ALC

The AL-80B is one of the few amplifiers using a "true" automatic level control (ALC) circuit. In this amplifier, the ALC actually samples grid current and power supply loading to determine the ALC voltage. The front panel "ALC SET" knob adjusts the level of grid current where ALC action begins. ALC action begins softly over a range of a few milliamperes to minimize distortion. This soft-touch ALC is an Ameritron exclusive.

The ALC circuit is located on the METER BOARD P/N 50-0080-3 (behind the "MULTIMETER" switch). IC301 (pins 9 and 10) compares the voltage drop (caused by grid current) across R106 in the main power supply board. ALC voltage is derived by comparing the grid shunt voltage to the voltage from the power supply.

The output of IC1 (pin 8) will go negative if the grid shunt voltage exceeds the voltage from divider R311 and R2 (chassis mounted control), or if the supply voltage sags from excessive line voltage drop. Pin 8 is followed by current buffer Q303 that sources the negative ALC voltage to the ALC output jack.

This amplifier includes an ALC Limit control on the rear panel. This control reduces overshoot and eliminates "motor-boating" (a slow rhythmic fluctuation) in the transmitted signal. These problems are caused by excessive transceiver ALC attack time delay. This control sets the maximum voltage level available from the ALC circuit. Adjustment details are given on page 15.

Dynamic Bias

Conventional bias circuits force high power linear amplifiers to dissipate hundreds of watts during low or no signal periods. This creates needless heat, since virtually no dissipation is required unless the amplifier is being driven with large signal levels.

The AL-80B 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-80B has a full resting period of very low dissipation between dots and dashes on CW and between words on SSB. The lower idling current reduces component temperature on both CW and SSB. If only a few milliwatts of RF power are applied to the amplifier, the quiescent current will increase. Linearity remains excellent with this circuit because the tube can remain biased for class AB operation without unnecessary standing dissipation.

The dynamic bias circuit is located on the Power Supply Board P/N 50-0080-1. Diodes D101 and D102 rectify a small sample of the RF drive voltage. This voltage is applied to the base of dc switch Q101. If Q101's base is driven with a few microamperes of current from the RF sampling circuit, Q101's collector will pull the base of PNP transistor Q102 low. This turns dc switch Q102 on.

When Q102 is on, zener diode D103 is connected between the collector and base of Q103. D103 sets the operating bias. This zener applies forward bias to Q103's base whenever the collector

voltage of Q103 exceeds the voltage of D103. This forward bias will turn Q103 on harder and will reduce the collector voltage. If the collector voltage is less than the breakdown voltage of D103, Q103 will move towards cut-off and the collector voltage will increase. Q103 functions as a current buffer for zener diode D103.

AL-80B Instruction Manual

Power Supply

Filament Supply

The filament circuit of this amplifier satisfies all requirements of the tube manufacturer related to tube performance and life. The filament voltage and inrush current are controlled by the power transformer's internal resistance and impedance, filament choke resistance, filament wiring resistance, and the step-start circuit. NEVER replace any circuit components or wiring with substitute parts. This precaution will insure maximum life for the tube.

Plate (HV) Supply

The plate supply uses a full wave doubler circuit with 200 amp surge rated diodes and a heavy duty 26 pound grain oriented transformer. Filtering is accomplished by a bank of high quality computer grade capacitors totaling 26 mFd. Large 50k ohm, 7 watt bleeders are used for safety and superior voltage equalization. The transformer allows user selection of fourteen different line voltages (see the "Transformer Connections" section on page 12 for details).

Power is supplied through "OFF-ON" switch S2. A 10 ohm resistor (R27) limits the line current during the filter capacitor charge time to lower component stress. When the filter capacitor charging current decreases sufficiently, RLY102 shorts the 10 ohm resistor. This applies full power line voltage to the transformer. The 10 ohm resistor is protected from high-voltage supply shorts by a 2A slow-blow fuse (F101) during start-up. If F101 or the 10 ohm resistor (R27) fails the amplifier will not start. If F101 fails from a momentary HV to ground fault, meter protection diode D117 may also fail. See the "Metering Functions" section that follows for more information.

Meters

Current Meter (plate and grid):

The plate and grid current meter is located on the far left side of the front panel. This meter indicates the plate current (Ip) on the right-hand meter scale. This scale has a small picket every 25 mA, a large picket every 75 mA, and indicates 750 mA at full deflection.

The left-hand meter scale indicates the grid current (Ig). The small pickets on this "Ig" scale appear every 10 mA and the larger pickets appear every 50 mA. The full scale "Ig" reading is 250 mA.

The plate and grid meters in this amplifier normally indicate maximum grid current and maximum RF output at or near the same "PLATE" tuning setting. Maximum grid current and minimum plate current also generally occur at the same "PLATE" tuning setting.

NOTE:

D117 protects the overload circuit (if used) and the meters. This diode is located near the electrolytic capacitors on outside edge of the main circuit board. D117 will usually short if there is a large high-voltage-to-chassis current fault. The grid and plate current meters will not read correctly if this diode fails. If D117 is shorted the overload circuit (if used) may repeatedly trip and the grid current may appear excessively high before full power is reached.

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.

AL-80B Instruction Manual

Multimeter

The multimeter is the meter on the right. It continuously reads the forward peak envelope power on its left-hand scale (FWD). This scale is calibrated in 100 watt steps up to 2 kW.

The right-hand scale of this meter provides four metering functions that are selected by the "MULTIMETER" switch. These functions include the measurement of high voltage (HV), reflected power and SWR (REF), ALC voltage output (ALC), and relative ALC threshold (ALC SET). The MULTIMETER FUNCTIONS section that follows describes these functions in more detail.

Multimeter Functions

HV: The multimeter indicates the dc plate voltage applied to the PA tube when the

MULTIMETER switch is placed in the HV position. The correct scale to use is the ALC/ HV scale. This scale has a picket every 100 volts. Two zeros must be mentally added behind the numbers indicated on the meter scale (i.e. multiply by 100), so that "25"=2500 volts and "20"=2000 volts. Do not operate the amplifier if the high voltage is over 3200 volts with the amplifier on standby. See the "Transformer Connections" section on page 12 for information on correcting excessive high voltage.

REF: The multimeter measures the antenna (or load) peak envelope reflected power and the

SWR when the MULTIMETER switch is placed in the REF position. The full scale reflected power reading is 500 watts. This scale is marked every 10 watts below 100 watts, and every 100 watts from 100 to 500 watts.

Note:

ALC: The multimeter measures the output voltage of the ALC detector when in the ALC

ALC SET: The multimeter measures the approximate grid current that will produce ALC activity

The SWR of the load is measured when the "MULTIMETER" is in the REF position by observing the different red SWR curves. The forward and reflected power meter pointers will cross each other on, or near, the correct SWR curve.

position. The full scale ALC reading is 35 volts and is read directly from the ALC/ HV scale. The meter should flick upwards occasionally during normal ALC action. See ALC Circuit operation on page 15 for more information.

when the meter switch is in the ALC SET position. One zero must be added to the reading on the ALC/ HV scale for this function. For example, ALC action will begin at approximately 150 mA of grid current (typically between 120 mA and 180 mA) when the "ALC SET" control is adjusted until the meter reads "15."

AL-80B Instruction Manual

Wattmeter Circuit

The AL-80B wattmeter circuit uses an accurate directional coupler followed by a true peak detector circuit. This circuit will accurately determine the true peak envelope power (PEP) of normal voice waveforms. If the load SWR is high, the true power reading will be obtained by subtracting the reflected power from the forward power.

Peak Envelope Power vs. Average Power

Peak envelope power (PEP) is often misunderstood by amateurs. PEP is not associated with the sine wave or root-mean-square (RMS) power, and PEP has no fixed ratio to average power on any mode except FM, FSK or CW. It is impossible to use a formula or "rule of thumb" approximation to convert between average and peak voice waveform powers.

PEP is the power at the crest (highest point) of the RF envelope waveform. On SSB, the average power can vary from a few percent of the PEP to over half of the PEP. Generally, the PEP on SSB is two to five times greater than the average power. A 50 watt average power SSB signal could have peak envelope powers that are lower than 100 watts or that exceed 250 watts.

On CW and other constant amplitude modes (such as FM or RTTY), the PEP is always equal to the average power. On CW, FM or RTTY 1000 watts of average power produces exactly 1000 watts of PEP.

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