>Printed in U.S.A.
500 WATT
SOLID STATE MOBILE AMPLIFIER
PLEASE READ THIS MANUAL BEFORE OPERATING THIS EQUIPMENT !
The Ameritron ALS-500M is a 500 watt PEP output solid state linear amplifier using rugged, conservatively rated bipolar RF
devices in the power output section. The ALS-500M operates at full power with continuous frequency coverage from 1.5
through 21.6 MHz. This amplifier requires no tuning adjustments. Broad band 5 pole filter provide output harmonic
suppression in excess of 60 dB for all frequencies above 8 MHz, and more than 70 dB on all TV channels. Export
modifications are available to extend operation to 30 MHz with a copy of a valid amateur license.
The ALS-500M uses two pairs of 2SC2879 transistors operating at 13.8 volts nominal in a push-pull output configuration.
High quality RF components combine with load fault sensing, temperature protection, and one switch frequency selection to
make this one of the simplest and easiest to operate amplifiers today. The ALS-500M operates on 13.8 Vdc electrical systems
and draws a peak current of 80 amperes at full output.
WARNING: THIS AMPLIFIER IS DESIGNED FOR USE IN VEHICLES
WITH NEGATIVE GROUND 12 VOLT ELECTRICAL SYSTEMS ONLY.
The battery should be maintained between 13.8 and 16.5 volts dc. ALS-500M
Instruction
Manual

i
TABLE OF CONTENTS

ALS-500M Features........................................................................................................ 1
General Information ........................................................................................................ 2
Load Fault Circuit ............................................................................................... 2
Bias Control Circuits........................................................................................... 2
Drive Power......................................................................................................... 2
Supply Voltage.................................................................................................... 3
SWR Considerations ........................................................................................... 3
Periodic Maintenance.......................................................................................... 3
Technical Assistance ........................................................................................... 3
Export Modifications........................................................................................... 4
Installation....................................................................................................................... 4
Location............................................................................................................... 4
Power Requirements ........................................................................................... 4
Fuse Holder Installation ...................................................................................... 5
Auxiliary Battery Installation.............................................................................. 5
Grounding........................................................................................................................ 6
Unibody Vehicles................................................................................................ 6
Frame-Type Vehicles .......................................................................................... 6
Interconnections Diagram ............................................................................................... 7
Interconnections .............................................................................................................. 8
Operation......................................................................................................................... 9
ALS-500M Parts List ...................................................................................................... 10
Combiner Board Parts List.................................................................................. 10
Power Amplifier Board Parts List....................................................................... 11
Output Filter Board ............................................................................................. 13
Bias Board Parts List........................................................................................... 15
Chassis Components Parts List ........................................................................... 17



ALS-500M
Instruction
Manual

1
ALS-500M FEATURES

1. Rugged
devices.

The ALS-500M uses four rugged linear RF power devices.

2.
Fast warm-up time.

The ALS-500M has no vacuum tubes to warm-up.

3.
No tune operation.

Tuning adjustments are not necessary. A simple one knob selector switch permits operation on

frequencies between 1.5 and 21.6 MHz.

4.
Load Fault Protection

The PA load impedance is monitored and the amplifier is bypassed if the bandswitch setting or
the external load is incorrect.

5. Current
meter.

The ALS-500M has a DC current meter to monitor collector current.

6. Off/On
switch.

This switch allows the amplifier to be by-passed for "bare-foot" operation without disconnecting

the high current leads.

7.
Remote Off/On control.

A separate connection on the power connector allows low current control of the amplifier Off/On

function for remote mounting.

8.
Remote A and B.

Ports A and B are for connecting the ALS-500RC. The ALS-500RC is a remote control head
that allows the amplifier to be located away from the operating station and still have access of the
front panel controls.

9. Compact size.

The ALS-500M weighs only 7.5 pounds and measures 3 3/4"H x 9"W x 15 1/2"D .
ALS-500M
Instruction
Manual

2
GENERAL INFORMATION

Load Fault Circuit
The ALS-500M features a load fault trip circuit that bypasses the amplifier if the amplifier frequency
switch is set to a lower frequency range than the exciter or if the load reflected power exceeds 70-100
watts. This circuit virtually eliminates the danger of component failures due to operating errors.

The Combiner circuit board near the PA contains the components that sense the reflected power at the
input of the low-pass filters used in the output circuit. Selecting a filter that has a cut off frequency
below the operating frequency or operating into loads with reflected power levels that exceed 70-100
watts will trip the overload and bypass the amplifier. SCR (Q5) on the Bias board keeps the amplifier
"locked out" until the POWER (ON/OFF) switch is cycled off and on.

Bias Control Circuits
The Bias board contains the temperature and bias control circuitry. The output transistor temperature is
monitored with diodes D1 and D2 on the PA module. The voltage drop across the diodes decreases as
the PA transistor temperature rises. The reduction in diode voltage with increasing temperature causes
IC 1c/d to reduce the PA base bias current supplied by Q2/3. Diodes D1/2 on the bias board limit the
available bias voltage if a failure in the bias circuit occurs.

IC 1a compares the voltage from the Power Amplifier temperature diodes to the reference voltage from
the temperature sensitivity control R28. If the temperature becomes too high (voltage too low) IC 1a
switches high and Q4 turns the cooling fan on. If the temperature continues to increase IC 1b will
eventually pull low and the voltage for the transmit relay and the bias voltage will be removed. The
THERMAL OVERLOAD LED is illuminated when the output of IC 1b is low. This circuit
automatically resets when the temperature drops to a safe operating range.

If the band switch is in the wrong position, the antenna SWR is high, or the amplifier is being driven
into non-linear operation a "load fault" will occur. When a load fault occurs gate voltage is applied to
SCR Q5. This causes Q5 to latch in a conducting state. Q5 will remain in this condition and the
amplifier's relay line will be disabled until the OFF/ON switch is cycled off and on. The LOAD
FAULT LED on the front panel is illuminated whenever SCR Q5 is in conduction and the amplifier is
bypassed from a load fault.

Drive Power
The ALS-500M normally requires much less than 100 watts of drive to produce full output power.
This drive power varies considerably with the gain of the transistors used in the amplifier and the
power supply voltage. As a general rule, exceeding 100 watts of drive for long periods of time may
cause component failures. Exceeding 70 watts of peak drive power may cause distortion and increase
the bandwidth of the transmitted signal.
ALS-500M
Instruction
Manual

3
Supply Voltage
Low voltage solid state amplifiers are very sensitive to power supply voltage changes. For maximum
performance, the voltage should be maintained as high as possible consistent with component life. The
devices used in this amplifier have demonstrated excellent life with supply voltages up to 16 volts, and
will produce the rated output power at 14 volts dc. The output power will decrease by approximately
85 watts per volt as the supply voltage is lowered from 14 to 12 volts.

SWR Considerations
SWR (Standing Wave Ratio) causes higher voltages and/or currents to appear at the output connector
of the amplifier. This problem occurs with all amplifiers regardless of whether tubes or
semiconductors