Ameritron AL-811 Service manual

PLEASE READ THIS MANUAL BEFORE ATTEMPTING TO OPERATE EQUIPMENT!!

UNPACKING INSTRUCTIONS

1. Carefully lift the amplifier by the bottom cabinet edge out of the shipping carton. Place the

amplifier on a firm, level surface and carefully inspect it for shipping damage. Contact the
shipper immediately if any damage exists. Do not discard the carton or packing material.

2. Remove the twelve screws holding the cover on with a number 2 phillips screwdriver.

Carefully lift the cover off the amplifier. Save the screws to resecure the cover.

3. Locate the fuse pack with the two 12 amp fuses and fuse caps. If additional screws are
needed, they will be in the fuse pack also. NOTE: Fuses supplied are for 120/110/100V

operation. If you are rewiring the AL-811 for 240/230/220V operation, you must use 8
amp fuses. The AL-811X export model is pre-wired for 240V operation and is supplied with

8 amp fuses.

4. Remove the foam packing material (left side, front view) that secures the 811A tubes during
transit. Carefully unwrap the tubes. Do not dislodge the Aluminum shaft that is connected to
the rear input bandswitch wafer.

5. To install the tubes in the sockets be sure the large diameter pins line up with the two large
diameter holes in each socket. Do NOT rock or twist the tubes excessively during the
installation. If the tubes are already installed, check the tubes for proper seating. If
necessary, press the tubes down into their sockets with gentle force. Do not rock or twist the
tube(s) excessively. Also check that the anode caps are secure and did not come loose during
the unwrapping process.

6. The white ceramic anode connectors will have to be removed from the top metal cap of each
tube if it ever becomes necessary to remove the tubes from the amplifier. This can be a
difficult procedure because of the high clamping force of the internal springs in the anode
connector may hold it to the cap very tightly. The tube will break if direct upward or rocking
pressure is applied in an attempt to remove the connector. The safest way to remove the
ceramic connector is to lift the tube out of its socket. A twisting or spinning pulling motion
can then be applied while holding the ceramic connector firmly until the tube and connector
are separated. Repeat the procedure for the other tubes.

7. Install the cover with the vent holes to the left (near the tubes) by installing the back screws
first. Install all the screws loosely and tighten them only after all the screws are in place.

8. Install the fuses and fuse caps on the back of the unit. Read the manual to become familiar
with the operation of the AL-811 amplifier.

AL-811 LINEAR AMPLIFIER

FEATURES

The AL-811 is a grounded grid linear amplifier
developed by Ameritron using low cost 811A power
triodes. It operates in class AB2 for SSB and CW.

1. Fast Warm Up Time: The 811A tubes take

approximately 3 seconds to warm-up.

2. Long Tube Life: The 811A tubes are long life,

reliable transmitting tubes. 811A tubes offer
rugged, reliable operation even on RTTY and
SSTV

3. Tuned Input: A Pi-Network tuned input

matches the 811A tubes to 50 ohm exciters.

4. Two Illuminated Panel Meters: The AL-811

has two illuminated panel meters. The Grid
Current meter provides a continuous reading of
the 811A grid current to indicate proper loading
of the amplifier. The other meter switches
between high Voltage (HV) and Plate Current
(Ip).

5. Safety Interlock: Removes AC from the unit

when the cover is removed. Never attempt to
defeat this switch.

6. Operate/Standby Switch: Used to remove the

amplifier from the RF line while filament and
plate voltages are maintained for "barefoot"
operation.

TECHNICAL SPECIFICATION AL-811

*

Frequency Coverage

Domestic model(AL-811): 160, 80, 40, 30, 20, 17
and 15 meter bands
Export model(AL-811X): 160, 80, 40, 30, 20, 17, 12
and 10 meter bands.

Input

Circuit type: Pi-Network, slug tuned coils
Maximum VSWR at resonance: 1.3:1
Minimum 2:1 VSWR bandwidth: 15%
Maximum drive power permissible: 100 watts
Typical drive for rated output: 75 watts

Output

Circuit type: Pi-Network
1/2 hour carrier: 400 watts
30 second carrier: 550 watts
1/2 hour PEP two tone: 600 watts
30 seconds PEP two tone: 600 watts
Efficiency: typically 65%

Power Supply

Circuit type: full wave bridge
Full load current: 550mA
Regulation: 12%
Maximum draw at rated output: 8A

7. XMT Indicator LED: Provides a front panel

indication of proper amplifier keying by the
exciter during operation.

8. ALC Voltage: The drive level is detected to

provide a negative control voltage for the exciter.
ALC prevents overdriving of the linear and
reduces distortion from excessive drive power.

CAUTION: This amplifier must be disconnected
from the power mains before removing the cover.
See the precaution on page 7.

Metering

Multimeter: reads HV and plate current
Grid meter: reads PA grid current

Connectors

Relay: keys amplifier when grounded. Sources +12

VDC open circuit and supplies 100mA when
grounded. A built-in pulse canceling diode

protects the exciter.
RF input: SO-239, 50 ohm input.
RF output: SO-239, 50 ohms needed with full power,

will load into any SWR below 3:1 at
reduced power output.

Power: NEMA 15-15P 120V grounded style.

Physical

Dimensions: 16" D x 13 ¾" W x 8"
Weight: 30 lbs.

*

specifications are subject to change without notice or obligation

2

GENERAL INFORMATION

SAFETY INTERLOCK

The interlock switch closes to allow AC line voltage to reach the
power transformer as long as the AL-811's top cover is in place.
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. WARNING:

never remove the cover of this amplifier with the unit
plugged into the power line.

DRIVING POWER

This amplifier is designed to operate at full ratings when it is
driven by an that has aproximately 70 watts of RF output. You
can use an exciter that has lower output power, but the
amplifier's output may be less. If you use an exciter that delivers
more than 70 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 readily available way
of determining the amplitude of the voice peaks which, if
excessive, can cause "flat topping" and splatter.

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.
Nonlinear operation may occur if you turn the control past
this point.

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.

ALC CIRCUIT

The ALC circuit converts a portion of the RF drive voltage at
the exciter end of the tuned input circuit to a negative going
control voltage. This voltage should be used to limit the exciter

drive to safe drive levels for the AL-811 for exciters that

develop more than 70 watts of output power.

A capacitive divider consisting of C27 and C28 is used to reduce
the RF voltage and drive a rectifier circuit consisting of D17 and
D18. The resulting voltage is filtered by C29 and R12 and
applied to the ALC potentiometer R14. R13 provides RF and
DC isolation for the ALC jack. The DC isolation prevents
loading of the exciter ALC input line by the ALC potentiometer.

ALC control on the amplifier adjusted to a point just before the
drive begins to decrease.

NOTE: The primary use of the ALC function is the prevention
of excessive drive levels. This circuit will not prevent small
changes in output power from occurring on different bands.
Destructive levels of drive power are those above 100 watts
under most conditions. Slight changes may occur in maximum
output power on different frequencies with the ALC connected.
A compromise in ALC adjustment may be necessary to achieve
acceptable performance on all bands.

PLATE SUPPLY

The power supply in this amplifier uses a combination plate,
filament and control transformer. A buck boost winding is
provided to allow the user to compensate for low, medium or
high power line voltage. This amplifier is normally supplied
wired for the highest power line voltage setting. Never change
this setting unless you are positive that performance is suffering
due to low filament and plate voltages. The life of components
will be shortened drastically if the high voltage exceeds 1800
volts at rest. The diagram on page 4 shows proper wiring for
each voltage.

EXPORT MODIFICATIONS

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" following the serial number.
Standard frequency coverages are indicated in the chart on page

7.

TECHNICAL ASSISTANCE

Technical assistance is available during our normal business
hours on weekdays. The following information is required to
assist you with operational problems:

• Model and Serial Number;

• Date of purchase and dealer;

• An accurate description of the problem;

Meter readings at all stages of the tuning procedure 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
processing mail, please allow at least three weeks for a written
reply.

AMERITRON

116 Willow Road

Starkville, MS 39759

Telephone: [phone]

FAX: [phone]

The ALC circuit can be adjusted by loading the AL-811 slightly
beyond the recommended maximum values with the ALC line
disconnected. The ALC line can then be connected and the

3