AMERITRON AL 1500 User Manual

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AMERITRON AL-1500

FULL POWER

LINEAR AMPLIFIER

N MAN

The Ameritron AL-1500 is a 1500 watt output linear amplifier that

operates from 160 through 15 meters. The Ameritron AL-1500X is the

export model and covers 160 through 10 meters. The AL-1500J is the

export model for Japan and covers 160 through 10 meters. The AL-1500

uses a single 3CX1500A7/8877 tube in a class AB2 grounded grid circuit.

CW, FM and RTTY efficiency is improved by shifting the bias deeper into

class B. The heavy duty power supply and RF components, combined with

a forced air system utilizing a chimney, provide long service life for

expensive components. The AL-1500 is shipped factory wired for 240

volt, 50/60 Hz power mains.

PLEASE READ THIS MANUAL BEFORE OPERATING THIS E

UIPMENT!

116 Willow Rd.

Starkville, MS 39759

UNPACKING INSTRUCTIONS

1. Carefully remove the amplifier, transformer, and tube from their shipping cartons.

Inspect each item for visible damage. If any damage occurred during shipment,

notif

the trans

ortation com

immediatel

2. Save all packing materials in case you need to return your AL-1500(X/J) for factory

service. The cartons have been designed to give maximum protection for this

amplifier. Any units returned without proper packing may be damaged and shipping

claims cannot be made. Contact the factory before returning any units.

3. Remove the screws that hold the cover to the amplifier. Slide the cover back and

remove it from the amplifier. There is a small bag that contains the fuses, fuse caps

and the remainder of the chassis screws wrapped in the packing material around the

ode

ecto

4. Please read the GENERAL INFORMATION and SPECIFICATIONS sections before

attempting to install the transformer and tube. Please note that the tube chimney comes

factory installed around the tube socket. Go to the INSTALLATION section on page 4

to begin installing the transformer and tube.

5. This amplifier must always be disconnected from the power mains before removing

the cover. See the precaution on page 10. Please read the entire manual to become

familiar with the o

eration of the AL-1500

(

X/J

)

lifier.

NOTE: The AL-1500J is the Japanese export version of the AL-1500 amplifier. The

AL-1500J utilizes a special power transformer for use with 200V AC, 50 Hz. The

AL-1500J will perform to specifications with the special transformer installed and

will cover 24 and 28 MHz.

FEAT

1. High performance tube: the AL-1500 uses a single rugged

3CX1500A7/8877 tube.

2. High power gain: the 3CX1500A7/8877 features high

power gain. As little as 65 watts of drive power will pr

vide 1500 watts of out

ower.

3. SSB/CW switch: the bias voltage is switched to provide

the best linearity on SSB or the lowest dissipation on CW

eration.

proper operation of the amplifier. The other meter reads

Plate Voltage (HV), Plate Current (IP), Peak RF Watts

(

)

and ALC.

7. Operate/Standby Switch: filament and plate voltages are

maintained while allowing the amplifier to be bypassed

for "barefoot" o

eration.

8.12 Volt Auxiliary Jack: 12 volts at 100 mA is provided for

accesso

suc

ATR-1

4. ALC Indicator: the drive level is detected to provide a

control voltage for the exciter. ALC prevents overdriving

of the linear and reduces distortion from excessive drive

ower.

5. Vernier Plate and Load Adjustments: both tuning controls

have vernier 6:1 reduction drives for smooth tuning.

6. Two Illuminated Panel Meters: the AL-1500 has two il-

luminated panel meters. The Grid Current meter provides

a continuous readin

rid current and indicates

9. XMT Indicator LED: provides a front panel indication of

proper amplifier keying by the exciter during operation.

10. Grid Overload Circuit: this amplifier has a circuit that

protects the tube from excessive grid current. If 175 mA of

peak grid current is reached the "OPR" LED will no longer

light and the amplifier will go into a bypass condition. This

overload condition can be reset by momentarily putting the

STBY/OPR switch in the STBY position.

Caution: This amplifier must be disconnected from the power

mains before removing the cover. See the warning on page

10.

TECHNICAL SPECIFICATIONS AL

1500

Input:

Circuit type: Pi-network, slug tuned coils Maximum VSWR

at resonance: 1.3:1 Minimum 2:1 VSWR bandwidth: 20% of

center frequency Maximum drive power permissable: 100

watts Typical drive for full power output: 65 watts

Metering:

Multimeter: Plate current, plate voltage, drive/ALC, power

output (PEP watts)

Grid: Grid current

ALC: Ne

ative

oin

0-20V

ustable

hono

ack

Output:

Circuit type: Pi-L, Pi

/2 hour continuous carrier: 1500 watts 30 second

continuous carrier: 2500 watts

1/2 hour PEP two-tone test: 2500 watts plus 30 second

PEP two-tone test: 2500 watts

lus

Power Supply:

Circuit type: full wave bridge, capacitor input

No load voltage: 3600 V

Full load voltage: 3300 V

Full load current: 1 amp

Regulation: 10% typical

Transformer: 34 lbs., hypersil

Capacitors: 26 mfd total, computer grade

Maximum draw at rated output: 15 amps at 240V AC 50/60 Hz

Tube:

Type:(1) 3CX1500A7/8877

Continuous dissipation: 1500 Watts

Warm-up time: 180 seconds

Efficienc

CW: 65% t

ical

Efficienc

SSB

(

envelo

e crest

)

: 62%

MARS/WARC:

set to nearest hi

hest amateur band

Keying: Requires relay closure or sinking to ground of t 12V

DC at 100 mA

hono

ack

RF Connectors: S0239

Line Connector: NEMA 6-15P

240V st

Dimensions: 18

1/2 D x 17 W x 10 H

Wei

ht: 77 lbs.

Frequency Coverage: (AL-1500)-1.8, 3.5, 7, 14, 18 and 21

MHz. User modified models cover 24 and 28 MHz. (AL-

1500X/J) Export models-1.8, 3.5,7, 14, 18, 21, 24 and 28

MHz.

Third Order IMD at Rated Out

ut: -36 dB

GENERAL INFORMATION

SAFETY INTERLOCK

While the Amplifier's top cover is in place, the interlock switch

closes to allow AC line voltage to reach the power transformer.

When the top cover is removed, the interlock opens and

disconnects the line voltage. This does not discharge the bank

of power supply filter capacitors. Be sure to allow the filter

capacitors to discharge before you touch anything inside the

Amplifier. You can select the High Voltage function of the

Multimeter to check the high voltage potential. Never attempt to

defeat the safety interlock. WARNING- Never remove the cover

of this amplifier with the unit plugged into the power line.

mal continuous amateur operation at 1500 watt levels. Power is

applied through RLY2 when the 12V DC low voltage supply is

activated. A 10 ohm resistor limits the line current during the

filter capacitor charge time to lower the stress on components.

When the primary voltage approahces the full line value, RLY3

shorts the 10 ohm resistor and applies the full line voltage to the

plate transformer. The 10 ohm resistor acts as a fuse during

start-up if the high voltage supply has a short.

TIMER OVERLOAD BOARD

DRIVING POWER

This Amplifier is designed to operate at full ratings when it is

driven by an exciter that has approximately 65 watts of RF

output. You can use an exciter that has lower output power, but

the Amplifier's output will be less. If you use an exciter that

delivers more than 100 watts, carefully adjust the driving power

to avoid "over drive" and the creation of spurious signals, which

create needless interference to other operators. We highly

recommend that you use a monitor scope for continuous output

monitoring. The display on an oscilloscope is the best way of

determining the amplitude of the voice peaks which, if

excessive. can cause "flat topping" and splatter. This amplifier

has a circuit that protects the tube from excessive grid current. If

175 mA of peak grid current is reached, the "OPR" LED will no

longer light and the amplifier will go into a bypass condition.

This overload condition can be reset by momentarily putting the

STBY/OPR switch in the STBY position.

IMPORTANT: In no case should you advance the power output

control of your exciter beyond the point where the Amplifier's

Power Output indication ceases to increase. If you turn the

control past this point, nonlinear operation may occur.

FILAMENT SUPPLY

The filament circuit of this amplifier satisfies all requirements

of the tube manufacturer related to tube performance and life.

Inrush current is controlled by the transformer internal

resistance and impedance, filament choke resistance and

filament wiring resistance. To insure maximum life of the tube

never replace any circuit components or wiring with substitute

parts.

The AL-1500 has a circuit board mounted on the front panel

side of the filter capacitor board that provides time delay to

insure the cathode of the 3CX1500A7/8877 has reached proper

operating temperature before high voltage and RF drive power

can be applied. This board also samples the peak grid current

and removes drive if the grid current is excessive.

The timer portion if this circuit board uses IC1A as a com-

parator to drive the complimentary darlington 01 and 02. When

twelve (12) volts is first applied to terminal "Y" diode D3

provides a regulated 5.1 volt reference. Divider R8 and R7

reduces the reference voltage to 3.7 volts. C9 charges from

current supplied by R9. After approximately three minutes, the

comparator output (pin 1) goes high. Q3's collector goes low

and turns on Q2 and Q1. If the 12 volt supp!y is momentarily

interrupted diode D1 discharges C9 through R6, R7, and R8.

Any interruption of more than a few seconds requires a

complete timing cycle to begin again.

The grid overload circuit compares the voltage developed

across the grid shunt (.3V equals 200mA) to the .256V reference

provided by R5 and R11. This sets the grid trip at 175 mA. Pin 7

of IC 18 will go high and turn 04 on if the grid current reaches

175 mA. This will cause RLY 1 to latch on and remove the 12

volts from the antenna transfer relay in the amplifier. The circuit

is reset by putting the amplifier on standby momentarily. This

removes the voltage that holds RLY 1 locked on. NOTE: The

grid overload circuit will respond much faster than the grid meter

can indicate grid current. if the overload continuously trips, the

likely cause is excessive peak grid current. This is caused by the

loading control being set too low (counter-clockwise) for the

peak drive power applied to the amplifier.

EXPORT MODIFICATIONS

The low voltage tap on the filament transformer primary pro-

vides the ability to operate the blower at slower speeds for

reduced noise. Normal amateur operation in CW and SSB will

not cause heat damage to components on any recommended tap.

It is always advisable to use the maximum speed (air flow) that

the level of noise permits to extend component life. Wiring

information for the blower is shown in the "Transformer

Connections" instructions.

PLATE SUPPLY

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 and have an "X or J" following

the serial number. Standard frequency coverages are indicated

in the chart following the tuning instructions on page 10.

The plate supply has a full wave bridge rectifier and a 1.8 KVA

CCS rated tape wound hypersil transformer. Filtering is

accomplished by a bank of high quality capacitors totaling 26

mfd (additional capacitance will not improve supply

performance). The Plate Supply will not be harmed by nor

METERING FUNCTIONS

The AL-1500 has two illuminated meters. The Grid Current meter

provides a continuous indication of the 3CX1500/8877 grid

current. This exclusive feature of Ameritron amplifiers indicates

proper amplifier operation better than any other parameter. Do

not exceed 75 mA on this meter during normal operation of this

amplifier. The other meter reads Plate Voltage (HV), Plate

Current (IP), Peak RF Watts (PO) and ALC. These functions are

selected with the Multimeter Switch.

Plate Voltage (HV): Read DC Plate Voltage on the 4000 volt

scale. This scale is 100 volts per division. Normal voltages are

3600 volts no load, 3300 volts full load.

R5 on the Meter Board (50-01140-1) adjusts the calibration of the

power meter.

ALC: Indicates a relative drive level (average, not PEP) that can

be estimated by dividing the Peak RF Watts scale by 10.

TECHNICAL ASSISTANCE

Technical assistance is available during our normal business

hours on weekdays. The following information is required to

assist you with operational problems:

1. Model and Serial Number

Plate Current (Ip): Read DC Plate Current on the 1000 mA scale.

Thi

25 mA

Peak RF Watts (PO): Read Peak RF Watts on the 2000 watt

scale. This scale has 50 watt divisions below 1000 watts and 100

watt divisions above 1000 watts.

NOTE: This circuit uses an emitter follower to charge a

capacitor to the peak envelope voltage detected by the

ALC/Power Board. Accurate peak envelope power readings are

given when the amplifier is connected to a 50 ohm nonreactive

load. If the amplifier is used with a mismatched load, the power

meter will read higher or lower than normal by a ratio up to the

value of the SWR. Potentiometer

2. Date of

urchase and dealer

3. An accurate descri

tion of the

roblem

Meter readings at all stages of the tuning proceedure 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

rocessin

mail

lease allow at least three weeks for a writ

ten re

.AMERITRON 116

Willow Road

Starkville, MS 39759

Tel: (662) 323-8211

Fax:

(

662

)

323-6551

PERIODIC MAINTENANCE

The high voltage present on the plate choke and air variable

capacitors attracts dust and dirt out of the air stream. It is

particularly important that the high voltage areas at the bottom of

the plate choke and the insulators on the air variable capacitors be

dust free. These areas should be inspected every few months if

the amplifier is operated in a dusty environment. Unplug the line

cord, and wait about 90 seconds until the power supply capacitors

discharge. Check the HV scale for zero voltage before removing

the cover. Remove the cover. You must first connect a jumper

wire from ground or chassis to the anode connection of the tubes.

NOTE: This is a safety wire that must be installed when

beginning service work. After service is complete, reverse the

procedure to remove the safety wire. Remove the wire from the

anode connection first and then from ground.

Use a soft bristle brush dipped in alcohol to clean areas men-

tioned previously. In the event that cleaning is required at

frequent intervals, place a low restriction air filter material over

the air inlet holes on the left front side of the cabinet near the

filter capacitors. Most hardware stores stock suitable materials

that are used as replacement filters for window air conditioners.

INSTALLATION

TRANSFORMER INSTALLATION

Remove the cover of the amplifier. Remove the small package

that is wrapped around the anode connector. This is the fuse pack

and contains the fuses, fuse caps and the remainder of the chassis

screws. Remove the top 7/16" nuts from the four transformer

mounting bolts inside of the amplifier. Carefully remove the

transformer from its shipping carton.

Place the transformer on the four

/4-20 mounting bolts. Use care

because the transformer is heavy. The side with the two high

voltage secondary RED leads must be adjacent to

the center panel(see Fig. 1). Now place a 7/16" nut on each bolt

(see Fig. 2). Snug the nuts down manually. Do not tighten with a

ratchet wrench.

Remove the brass

/4" hex nuts and the top flat washer from the

two 6-32 screws on the rectifier board (see Fig. 1). Install the

RED lead ring terminals on the screws and replace the flat

washers and 1/4" hex nuts. Position the wires so that the black

insulated areas are at least 1/4" from each other and any metal

ects. Now ti

hten the 1/4" hex nuts.

TRANSFORMER INSTALLATION Cont. Fi

. 3

For 240V Operation (factory wired):

The four primary leads have colored plastic insulating boots

over the quick disconnect terminals. Slide these back prior to

installing the leads. !nstall the color coded boots as

follows:(see Fig. 1) Note: Japanese export model (AL-1500J)

should follow the 240V operation steps to properly connect

their transformers. The AL-1500J is supplied with a special

transformer for 200V operation.

1. BLUE (Brown wire) to the top relay terminal

2. YELLOW (Black/White) to the top terminal of terminal

block

3. CLEAR (Black wire) to the second terminal of terminal

block

4. RED

(

Brn/Wht

)

to the bottom terminal of terminal block

Now slide the colored insulating boots back over the ter-

minals. Note: The green wire is not used for 240V operation.

There is no green wire on the AL-1500J export model

transformer.

Important: The leads must be in the positions indicated by

the color coded insulating boots(see Fig. 1) for 240V opera-

tion. Or for 200V operation in Japan. Caution: Do not use

the 220V wiring unless the line voltage is always below 220

tan

lta

240

t 220

For 220V operation (see Fig. 3), follow the first three steps

above, then follow the steps below:

1. Slide the RED boot back on the BRN/WHT

wire.

2. Clip the terminal connector off the wire and slide

the RED boot off.

3. Remove the restraint from the GRN wire and

slide the RED boot on to the wire.

4- Solder the terminal connector to the GRN wire.

TUBE INSTALLATION

Note that one of the tube pins is larger in diameter. This

larger pin "keys" the tube base and socket. Install the tube by

aligning the tube pins with the socket contact terminals, then

seat the tube with vertical pressure ONLY. Do not "rock" or

"twist" the tube. Also the chimney is already mounted inside

the AL-1500 am

lifier.

After the tube is installed, attach the anode connector as

follows: (Refer to the Fig. 4)

. Remove screw "A" that holds the anode con-

nector to the 500pf blocking capacitors.

2. Attach the anode connector to the tube anode.

3. Insert screw "A" into the 500pf capacitors and

snug it down.

Fig. 4

5. Tape up the BRN/WHT wire because it will 5

not be used. To

View of 1500 Tube

Caution: This page is only valid for transformers that contain these exact color codes for the primary winding. Early

production units did not contain a multiple tap transformer. If the terminal strip has all these color coded wires, then the

unit has the multi

le ta

transformer.

FILAMENT/BLOWER WIRING INSTRUCTIONS

The AL-1500 and 1500(X) amplifiers come prewired for 240V line voltage and with the blower prewired for medium

high fan speed. NOTE: The AL-1500J Japanese export model is prewired for 208V line voltage. This page gives filament

transformer connection details for various line voltages and blower speeds. The five lug terminal strip and the single lug

terminal strip are located immediatgly behind the ON/OFF rocker switch inside the unit. The drawing below shows the

connection of transformer leads and their

ose.

This chart shows the color code of the transformer leads and their purpose. The number in paren-

thesis indicates the number of the terminal lug that the transformer lead is connected to. The

number three (3) lug is not used to change the filament or blower wiring. Do not add or remove any

wires from the number three (3) lug. Refer to the drawing above. Use the lug numbers above when

referrin

to both of the Filament connection chart and the Blower connection chart below.

FILAMENT TRANSFORMER LINE VOLTAGE T

ere

are two wires that connect to the terminal lugs which

determine the Filament Line Voltage. The BLACK wire

from the power switch and WHITE wire from rear of the

unit connect to different terminal lugs depending on the

voltage desired. The AL-1500 and 1500(X) come prewired

for 240V operation*. AL-1500J comes prewired for 200V

operation**. Refer to the chart below. The voltage listed in

the chart below is the maximum line voltage that should be

applied to a given tap. Operation with line voltage in

excess of 'he tan voltage selected can result in a reduction

of tube life

BLOWER CONNECTIONS

The GREEN and WHITE wires from the rear of the unit

connect to the terminal lugs to control the air speed of the

fan. The AL-1500/X/J are prewired for the medium high

speed setting*. Refer to the char below. The blower

connections can be moved to lower speed taps if air noise

is excessive. Ameritron recommends using the highest

speed tap that noise considerations permit. The lowest

speed tap will develop sufficient air flow for standard

amateur SSB and CW full power operation. The highest

speed taps should be used for contest or RTTY operation.

INTERCONNECTION

1. Connect the RF output of the exciter to the RF IN connector

on the rear of the AL-1500 with 50 ohm coax. Use any good

quality 50 ohm cable long enough to connect the amplifier to

the exciter. The amplifier uses a standard SO-239 female that

will mate to a PL-259 male connector on the cable.

2. Connect the existing station antenna system to the RF OUT

connector on the rear of the AL-1500 with RG-8 type coax.

This connection uses PL-259 connectors.

3. Use shielded audio type cable with standard male phono plugs

to connect to the RELAY jack on the AL-1500. This jack

has

ositive 12V DC o

en circuit and su

lies

100mA of current when

ulled to

round.

4. Connect a short ground lead from a good earth and RF ground

to the GND terminal.

5. The 12V connection on the rear panel provides 12V DC at 100

mA maximum to operate external dial lamps or accessories

such as the ATR-15 Antenna Tuner.

6. DO NOT CONNECT THE "ALC OUT" SOCKET ON THE

AMPLIFIER TO THE "ALC" SOCKET ON THE

TRANSMITTER UNTIL INSTRUCTED TO DO SO IN

THE TUNE UP PROCEDURE. This jack provides up to 20

Volts of ne

ative volta

e for transmitter

ain control.

LOCATION POWER CONNECTIONS

-Do not operate 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 air inlet for the blower. Do NOT place anything

that will impede the free flow of air within 2 inches of the

cabinet ventilation holes.

The AL-1500 is supplied with a NEMA 6-15P plug for 240V

AC operation. Operation with power main voltages below

200 volt is not recommended. Special transformers are re-

quired for 200V, 50/60 Hz operation (see NOTE on page 1).

Refer to the "Transformer Installation" section on pages 4

and 5 for the correct wirin

for 220 to 240 volt o

eration.

VENTILATION

The AL-1500 ventilation system has been designed and

tested to maintain tube seal temperature safely below the

tube manufacturer's rating at 1500 watts output with a 100%

duty cycle when properly tuned. The blower in the AL-1500

is a permanently lubricated type that requires no main-

tainence in normal operation. To insure proper ventilation in

your installation, 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 vent holes have o

en air circulation.

2. The exhaust air flow is over 30 CFM. Do not "assist" the

air flow unless the fan exceeds the AL-1500 blower

CFM b

a factor of 2:1.

t m

nt a

iti

nal fan

n th

AL-1500

4. The exhaust air will become quite warm at higher power

levels. Do not place any heat sensitive objects in the

exhaust air stream.

NEVER REWIRE THE POWER SUPPLY TO BOOST

THE HIGH VOLTAGE ABOVE 3700 VOLTS.

The wiring between the fuse box and the amplifier AC outlet

must be No. 12 gauge or larger in order to supply the current

required (13 amperes) without a significant drop in the line

voltage. The outlet should be fused for 20 amperes.

GROUNDING

Connect a good RF and earth or water pipe ground to the

ground post on the rear panel of the Amplifier. Use the

heaviest and shortest connection possible.

Before you use a water pipe ground, inspect the connections

around the water meter and make sure that no plastic or rub-

ber hose connections are used. These connections interrupt

electrical continuity to the water supply line. Install a jumper

around any insulating water connections you may find. Use

heavy copper wire and pipe clamps. It is best to ground all

equipment to one point at the operating position and then

ground this point as described above.

TUNING INSTRUCTIONS

Proper tuning of a grounded grid linear amplifier is best

accomplished with an understanding of what each control

does and what the meters are telling the operator about the

condition of TUNE.

ing operation. Excessive grid current, distortion on SSB or

arcing in the tank components occurs when full drive power

is applied to the amplifier without the "LOAD"' set for

enough clockwise (higher loading).

The tuning controls function as follows:

PLATE: This control tunes the amplifier output circuit to the

operating frequency. It should always be adjusted for

maximum output power or maximum grid current. Due to

interaction with the ''LOAD" control, a "touch-up" should be

performed after any load adjustments.

It is important to remember the loading must be set properly

for the PEAK power the amplifier is expected to develop. 50

watts PEP will be the maximum drive the amplifier will

safely handle if the output of the amplifier is tuned with 50

watts of carrier drive. Any attempt to go beyond the amount

of drive power the amplifier was originally tuned at will

result in a rapid increase in grid current, splatter and even

damage to components.

LOAD: This control adjusts the coupling of amplifier to the

antenna or load. It should be adjusted to keep the grid

current in the proper operating range. As the loading

capacitance is reduced (by rotating the control to a higher

front panel number), the coupling is increased. An increase

in coupling will reduce grid current and increase the amount

of drive the amplifier will accept without component

damage.

A common mistake in tuning is to adjust the "LOAD"

control at low drive powers and apply more drive dur

The "LOAD" control should be adjusted for maximum

output power without exceeding the recommended grid

current. DO NOT USE THE LOAD CONTROL TO

REDUCE POWER IN A GROUNDED GRID AMPLIFIER.

The drive from the exciter should be reduced if the amplifier

plate current or output power is excessive. The "LOAD"

setting should be increased if grid current is excessive. Any

errors in adjusting this control should be made in favor of a

higher load setting (clockwise).

INSTALLATION Cont.

CW PROCEDURE

Follow these instructions in numerical order. If the various meter

readings are different than indicated, check the connections from

the exciter to the amplifier and make sure they are correct.

Consult the manual for the exciter.

6. With exciter drive still at zero, place the MULTIMETER

switch in the Ip position. Observe the 1000 mA scale. The

meter should read zero (0). Place the STBYOPR switch in

the OPR

osition.

Be sure the transformer is correctly installed and wired for your

line voltage. See the "Transformer Installation" section on page 4

and 5 for wiring details.

1. Set the AL-1500 front panel switches as follows:

POWER TO OFF

OPR-STBY TO STBY

SSB-CW TO CW

LTIMETER T

2. Plu

the AC line cord into the

er volta

e outlet.

3. Set the Power Switch to the ON position. The grid meter

should light and the blower should start. After three minutes,

the plate meter should light and the multimeter should read

3600 volts nominal and absolutely no more than 3700 volts

HV.

4. With the amplifier still on STANDBY. tune the exciter into a

normal 50 ohm load according to the manufacturer's

instructions. Turn the exciter drive fully down after tuning.

5. Place the amplifier mode switch in the CW position, the

bandswitch on the same band as the exciter, the PLATE

control in the dial range for the band selected and the load

control as indicated:

7. Key the exciter (no drive) and observe the plate current on the

1000 mA scale. It should be 75 mA. Place the CW-SSB

switch in the SSB position. Plate current should now read

250 mA. Return the CW-SSB switch to the CW position.

Note: The no drive currents will vary up to 25% due to

lin

tage

ces.

8. Apply only enough drive to indicate a grid current of 50 mA or

an Ip of no more than 500mA. Tune the PLATE control for

maximum output power or grid current. It is normal for the

plate current to dip at this point. If the grid current

goes over 100 mA. reduce the drive at once. Unkey the

exciter. NOTE: This amplifier has a circuit that protects

the tube from excessive grid current. If 175 mA of peak grid

current is reached, the "OPR" LED will no longer light and

the amplifier will go into a bypass condition. This overload

condition can be reset by momentarily putting the

STBY/OPR switch in the STBY position. Repeated tripping

of the grid overload circuit usually indicates that the loading

control is set too far counterclockwise for the amount of

drive being applied to the amplifier or that something in the

antenna system is changing impedance (arching) during

9. Place the MULTIMETER switch in the PO position and

observe the 2000 Peak RF Watts scale. Increase the drive

until 100 mA of grid current is indicated. Adjust the LOAD

and PLATE controls for maximum output. The grid current

be lower now.

10. Advance the drive to 100 mA of grid current. Adjust the

LOAD and PLATE controls for maximum output power. The

out

ut should be over 1000 watts now.

11. Apply full drive without exceeding 100 mA of grid current.

The final grid current should be around 50 mA and the plate

current below 1000 mA.

ALC

(

Automatic Level Control

)

ALC will

revent over-

ower o

eration.

The primary use of the ALC is to reduce the input drive power

to a safe level for the AL-1500. The maximum drive that the

AL-1500 will tolerate is approximately 100 watts. At this drive

level the output of the AL-1500 may be in excess of 2000 watts

when properly tuned. The ALC should be connected and

adjusted after ;he amplifier is properly tuned on CW. Use a

shielded audio-type cable with a standard male phono connector

to connect the 0-20 volt negative ALC voltage to the exciter

ALC input. Consult the exciter manual for proper connection

details.

Settin

the ALC ADJ Control

Proper adjustment of the rear panel ALC control can be

achieved b

the followin

ste

1. Load the amplifier according to the tune-up instructions

(with the ALC disconnected from the exciter) to the desired

maximum power.

2. Connect the ALC line and rotate the ALC control fully

clockwise lookin

at the rear of the unit.

3. Set the MULTIMETER switch to the PO position or observe

an external PEP meter or oscillosco

4. Set the transmitter audio control about 20

16 higher than

normal.

5. Speak in the microphone in a normal tone of voice and

observe the reading on the 2000 RF Watts scale

6. Adjust the ALC ADJ control on the rear panel until the

amplifier output is no more than the desired maximum

ower obtained in ste

The exciter internal ALC will maintain linearit

the am

lifier

SSB PROCEDURE

Tune the Exciter and Amplifier as described in "TUNE-UP CW

PROCEDURE".

1. Place the SSB-CW switch in the SSB

osition.

2. Adjust the exciter gain control to permit voice peaks to reach

the same value the peak output meter read on CW when

fully loaded. The plate and grid currents should remain well

below 50% of the CW values during normal modulation.

SSTV, FM, RTTY, PACKET, AMTOR:

The plate current should be limited to 800 mA maximum. The

grid current should be limited to 50 mA. Tune the amplifier for

peak output power with the drive reduced to the grid and plate

current below the ratings given.

NOTE:

Some exciters will put out short duration high power RF pulses

when first keyed. Exciter power output peaks may reach or

exceed full output level even if the exciter's power control has

been adjusted to deliver reduced power under "keydown"

conditions.

The amplifier loading control must be set high enough

(clockwise) to prevent extremely high energy levels from

developing in the plate and grid circuits of the amplifier. DO

NOT "UNDERLOAD" THE AMPLIFIER TO REDUCE

POWER. Never "retune" the amplifier to produce higher ef-

ficiency with reduced drive. Poor linearity, splatter or even

damage to components may result from failure to follow these

instructions. Repeated tripping of the grid current circuit

usually indicates that the loading control is set too far counter-

clockwise for the amount of drive being applied to the amplifier

or that something in the antenna system is :hanging impedance

(arcing) during peaks.

WARNING!!

MAKE NO ATTEMPT TO PUT THIS AMPLIFIER IN SERVICE WITH THE COVER REMOVED!

CONTACT WITH VOLTAGES INSIDE THIS AMPLIFIER CAN BE FATAL! ALWAYS

DISCONNECT THE AMPLIFIER FROM THE POWER MAINS AND WAIT FOR THE FILTER

CAPACITORS TO DISCHARGE BEFORE REMOVING THE COVER.

PARTS LIST

AMERITRON AL 1500 User Manual

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