Ameritron AL-811H 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. Save the carton and packing material for possible
shipping in the future.

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 rescuer the cover. Note that the
AL811H is shipped with the fuses and fuse caps inside the amplifier.

3. Locate the fuse pack with the two 12 ampere 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 (Models AL-811H/HY). If you are rewiring the AL-811H for 240/230/220V
operation, you must use 8 ampere fuses. The AL-811HX export model is pre-wired for

240V operation and is supplied with 8 ampere fuses.

4. Remove the foam packing material (around the tubes) that secures the 811A tubes during
transit. Carefully unwrap the tubes. Do not dislodge or break the 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 them for proper seating. If necessary,
press the tubes down into their sockets with gentle force. Do not rock or twist the tubes
excessively. Also, check that the anode caps are secure and that they did not come loose
during the unwrapping process.

6. The white ceramic anode connector 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 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 with each tube.

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-811H amplifier.

AL-811H LINEAR AMPLIFIER

FEATURES

The AL-811H 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

10 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-811H 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. Multi-voltage Heavy Duty Transformer: A unique

"buck-boost" winding allows adjustment of primary
voltages to match a wide range of line voltages centered on
110 and 230 volts. This versatile Ameritron feature allows
the user to maintain optimum voltages on the tubes and
other components to obtain maximum performance and life.

6. Vernier Plate and Load Adjustments: Both tuning

controls have vernier 6:1 reduction drives for smooth tuning
logging scales for accurate and rapid tune-up.

7. Safety interlock: AC input power is removed from the
transformer when the cover is removed. Never attempt to

defeat this switch.

8. Operate/Standby Switch: Used to remove the amplifier
from the RF line while filament and plate voltages are
maintained during "barefoot" operation.

9. XMT Indicator LED: Provides a front panel indication of
proper amplifier keying by the exciter.

10. ALC: The drive level is detected to provide a control
voltage for the exciter. ALC prevents over-driving of the
linear and reduces distortion from excessive drive power.

11. Neutralization Circuit: Reduces unwanted feedback to
improve performance.

Domestic model(AL-811H): 160, 80, 40, 30, 20, 17 and 15

meter bands

Export model(AL-811HX/HY): 160, 80, 40, 30, 20, 17, 15, 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: 85 watts
Typical drive for rated output: 65 watts

Output (7MHz)

Typical SSB PEP voice operation: over 800 watts continuous
Typical CW continuous operation: 600 watts
1/2 hour PEP two tone: 650 watts
1/2 hour continuous carrier: 400 watts

ALC

Negative going, 0-12V, adjustable, phono jack

Power Supply

Circuit type: full wave bridge rectifier
No load voltage: 1700V
Full load voltage: 1500V
Full load current: 700mA
Regulation: 15%
Maximum draw at rated output: 10A (120V)
AC Input: 120V, 50/60 Hz (AL-811H/HY

240V, 50/60 Hz (AL-811HX)

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 with full power, into any SWR

below 3:1.
Power: NEMA 5-15P 120V grounded style.
ALC: Phono Jack. Supplies up to 12 volts of negative voltage

for ALC control of exciters.

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

TECHNICAL SPECIFICATION AL-811H

Frequency Coverage

*

Physical

Dimensions: 15.5" D x 13.75"W x 8.25"
Weight: 30 lbs.

*

Specifications are subject to change without notice or obligation.
Exact performance measurements may vary due to the accuracy of the test
equipment and the measurement methods used.

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GENERAL INFORMATION

SAFETY INTERLOCK

The interlock switch stays closed to allow AC line voltage to
reach the power transformer as long as the AL-811H's top cover
is in place. When the top cover is removed, the interlock opens
and disconnects the input 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 exciter that has approximately 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
could 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: Do not increase the drive power unless the
amplifier output power also increases. Grid current climbs
rapidly and the plate current meter and output power will
barely increase with excessive drive. This condition
indicates the amplifier LOAD control needs to be advanced
to a higher number. Excessive plate current indicates the
drive power limit has been reached. Non-linear operation,
splatter, and excessive grid current will occur if the
"LOAD" setting it too low.

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's 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-811H 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 is
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.
The ALC circuit can be adjusted by loading the AL-811H
slightly beyond the recommended maximum values with the

ALC line disconnected. The ALC line can then be connected
and the ALC control on the amplifier can be 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.
Under most conditions destructive levels of drive power are
those above 100 watts. 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. Never attempt to rewire this amplifier while it

is connected to power.

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 either "X" or "Y" following the serial
number. Standard frequency coverage is 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:

1. Model and Serial Number

2. Date of purchase and dealer

3. 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]

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METERING FUNCTIONS

The AL-811H has two illuminated panel meters. The right
meter reads PA grid current up to 200mA. The normal current
with a single tone (carrier) signal will be 150mA to 175mA. If
the current is too high during full power operation, the loading
control should be advanced to a higher setting.

INSTALLATION

LOCATION

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 any books,
magazines or equipment that will impede the free flow of air
near the sides of the cabinet.

VENTILATION

The AL-811H ventilation system has been designed and tested
to maintain the 811A tube temperature safely below the tube
manufacturer's rating at 500 watts output with a 100% duty
cycle. To insure proper ventilation in your installation, observe
the following:

1. Do not block or restrict the ventilation holes in the cover.

2. The exhaust air flow is over 20 CFM. Do not "assist" the
air flow unless the fan exceeds the AL-811H fan CFM by a
factor of 2:1.

3. Do not mount additional fans on the AL-811H cabinet.

4. The exhaust air will become warm at high power levels. Do
not place any heat sensitive objects in the exhaust air
stream.

GROUNDING

Connect a good earth or water pipe ground to the ground post on
the rear panel of the amplifier. Use the heaviest and shortest
connection possible.

If the current is too low, the loading control should be turned to
a lower setting. The left meter reads PA high voltage up to 2000
volts and plate current up to 750mA. The normal readings are
1400-1600 volts HV and 650mA of current at full rated output
with a single tone signal.

perform equally well with a power line frequency of 50 Hz or 60
Hz. The Transformer Connections chart at the bottom of this
page shows proper connections for various line voltages.

WARNING: The green wire connects to the chassis of the

amplifier and it must connect to the safety
ground of the outlet.

The AL-811HX (export model) is wired for 240V, 50/60 Hz
operation. The appropriate plug is not provided for this model.
You must wire the proper plug on the end of the power cord
supplied. Simply cut the existing plug off and wire the
appropriate plug in its place. If the line voltage in your country
is not 240V, then you must change the transformer to the
appropriate setting indicated by the chart below. Note: the AL­811H transformer allows operation on 100V line voltage in
countries such as Japan.

NEVER REWIRE THE POWER SUPPLY TO BOOST THE
HIGH VOLTAGE ABOVE 1800 VOLTS. ALSO, DO NOT
ATTEMPT TO REWIRE THIS AMPLIFIER WHILE IT IS
CONNECTED TO POWER.

The wiring between the fuse box and the amplifier AC outlet
must be 14 gauge or larger in order to supply the operating
current required (10 amperes) without a significant drop in the
line voltage. The outlet should be fused for the wire gauge used.

Before you use a water pipe ground, inspect the connections
around the water meter and make sure that no plastic or rubber
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.

POWER CONNECTIONS

The AL-811H is supplied with a NEMA 5-15P plug for 120V
operation. The power required to operate the AL-811H/HY is
not high enough to warrant 240V operation unless 120V is not
available. The fuses should be 12 ampere fuses for 120V and
they must be changed to 8 amperes for 240V operation. The
diagram to the right shows the proper wiring for 120V
operation.

Operation on a voltage of 240V is not required, nor will it
necessarily improve performance. The power transformer will

*Factory wired operation for the AL-811H
**

Factory wired operation for the AL-811HX

VOLTAGE BUCK BOOST PRIMARY

*

120 A to 1, B TO 2 C to D, E to F
110 1 to 2, (A,B OPEN) C to D, E to F
100 A to 2, B to 1 C to D, E to F

For 240, 230, 220 all three primary conditions apply ¯

**

240 A to 1, B to 2 no connection C to D
230 1 to 2, (A,B OPEN) D to E
220 A to 2, B to 1 no connection E to F

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